Repair and Maintenance of Window and Split AC

46 Shri TechnologiesShri Technologies The primary disadvantage of ductless air conditioners is their cost. Such systems cost about $1,500 to $2,000 per ton (12,000 Btu per hour) of cooling capacity. This is about 30% more than central systems (not including ductwork) and may cost more than twice as much as window units of similar capacity.\" An additional possible disadvantage that may increase net cost is that ductless systems may sometimes not be eligible for energy efficiency rebates offered by many electric utility companies as part of an incentive program to reduce summer cooling load on the electrical grid. Central (ducted) air conditioning Central (ducted) air conditioning offers whole-house or large-commercial-space cooling, and often offers moderate multi-zone temperature control capability by the addition of air-louver-control boxes. In central air conditioning, the inside heat-exchanger is typically placed inside the central furnace/AC unit of the forced air heating system which is then used in the summer to distribute chilled air throughout a res- idence or commercial building. Portable units A portable air conditioner can be easily transported inside a home or office. They are currently available with capacities of about 5,000–60,000 BTU/h (1,800–18,000 W output) and with or without electric- resistance heaters. Portable air conditioners are either evaporative or refrigerative. The compressor-based refrigerant systems are air-cooled, meaning they use air to exchange heat, in the same way as a car or typical household air conditioner does. Such a system dehumidifies the air as it cools it. It collects water condensed from the cooled air and produces hot air which must be vented outside the cooled area; doing so transfers heat from the air in the cooled area to the outside air. Portable split system A portable split system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, simi- lar to a permanently fixed installed unit. Portable hose system Hose systems, which can be monoblock or air-to-air, are vented to the outside via air ducts. The monoblock type collects the water in a bucket or tray and stops when full. The air-to-air type re-evaporates the water and discharges it through the ducted hose and can run continuously.

Shri Technologies 47 Repair & Maintenance of Window & Split AC A single-hose unit uses air from within the room to cool its condenser, and then vents it outside. This air is replaced by hot air from outside or other rooms (due to the negative pressure inside the room), thus reduc- ing the unit's effectiveness. Modern units might have a coefficient of performance of approximately 3 (i.e., 1 kW of electricity will pro- duce 3 kW of cooling). A dual-hose unit draws air to cool its condenser from outside instead of from inside the room, and thus is more effective than most single-hose units. Portable evaporative system Evaporative coolers, sometimes called \"swamp coolers\", do not have a compressor or condenser. Liquid wa- ter is evaporated on the cooling fins, releasing the vapor into the cooled area. Evaporating water absorbs a significant amount of heat, the latent heat of vaporisation, cooling the air. Humans and animals use the same mechanism to cool themselves by sweating. Evaporative coolers have the advantage of needing no hoses to vent heat outside the cooled area, making them truly portable. They are also very cheap to install and use less energy than refrigerative air condition- ers. Uses Air-conditioning engineers broadly divide air conditioning applications into comfort and process applica- tions. Comfort applications It aims to provide a building indoor environment that remains relatively constant despite changes in exter- nal weather conditions or in internal heat loads. Air conditioning makes deep plan buildings feasible, for otherwise they would have to be built narrower or with light wells so that inner spaces received sufficient outdoor air via natural ventilation. Air conditioning also allows buildings to be taller, since wind speed increases significantly with altitude making natural ven- tilation impractical for very tall buildings. Comfort applications are quite different for various building types and may be categorized as:  Commercial buildings, which are built for commerce, including offices, malls, shopping centers, restau- rants, etc.

48 Shri TechnologiesShri Technologies  High-rise residential buildings, such as tall dormitories and apartment blocks  Industrial spaces where thermal comfort of workers is desired  Institutional buildings, which includes government buildings, hospitals, schools, etc.  Low-rise residential buildings, including single-family houses, duplexes, and small apartment build- ings  Sports stadiums, such as the University of Phoenix Stadium and in Qatar for the 2022 FIFA World Cup. The structural impact of an air conditioning unit will depend on the type and size of the unit. In addition to buildings, air conditioning can be used for many types of transportation, including automo- biles, buses and other land vehicles, trains, ships, aircraft, and spacecraft. Domestic use Air conditioning is common in the US, with 88% of new single-family homes constructed in 2011 includ- ing air conditioning, ranging from 99% in the South to 62% in the West. In Europe, home air conditioning is generally less common. Southern European countries such as Greece have seen a wide proliferation of home air-conditioning units in recent years. In another southern European country, Malta, it is estimated that around 55% of households have an air conditioner installed. In India AC sales have dropped by 40% due to higher costs and stricter energy efficiency regulations. Process applications Process applications aim to provide a suitable environment for a process being carried out, regardless of internal heat and humidity loads and external weather conditions. It is the needs of the process that deter- mine conditions, not human preference. Process applications include these:  Chemical and biological laboratories  Cleanrooms for the production of integrated circuits, pharmaceuticals, and the like, in which very high levels of air cleanliness and control of temperature and humidity are required for the success of the process.  Environmental control of data centers

49 Repair & Maintenance of Window & Split AC  Facilities for breeding laboratory animals. Since many animals normally reproduce only in spring, hold- ing them in rooms in which conditions mirror those of spring all year can cause them to reproduce year- round.  Food cooking and processing areas  Hospital operating theatres, in which air is filtered to high levels to reduce infection risk and the humidi- ty controlled to limit patient dehydration. Although temperatures are often in the comfort range, some spe- cialist procedures, such as open heart surgery, require low temperatures (about 18 °C, 64 °F) and others, such as neonatal, relatively high temperatures (about 28 °C, 82 °F).  Industrial environments  Mining  Nuclear power facilities  Physical testing facilities  Plants and farm growing areas  Textile manufacturing  In both comfort and process applications, the objective may be to not only control temperature, but also hu- midity, air quality, and air movement from space to space. Questions 1. What are the different types of air conditioning systems 2. What are the uses of ductless air conditioning systems 3. What are the different comfort and process applications of air conditioning systemsShri Technologies

50 Shri TechnologiesShri Technologies Vapor Compression Refrigeration system Vapor-compression refrigeration, in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air-conditioning of buildings and automo- biles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and in- dustrial services. Oil refineries, petrochemical and chemical processing plants, and natural gas processing plants are among the many types of industrial plants that often utilize large vapor-compression refrigera- tion systems. Refrigeration may be defined as lowering the temperature of an enclosed space by removing heat from that space and transferring it elsewhere. A device that performs this function may also be called an air conditioner, refrigerator, air source heat pump, geothermal heat pump or chiller (heat pump). Description of the vapor-compression refrigeration system The vapor-compression uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the space to be cooled and subsequently rejects that heat elsewhere. Figure depicts a typical, single-stage vapor-compression system. All such systems have four components: a compressor, a conden- ser, a thermal expansion valve (also called a throttle valve or metering device), and an evaporator. Circu- lating refrigerant enters the compressor in the thermodynamic state known as a saturated vapor and is compressed to a higher pressure, resulting in a higher temperature as well. The hot, compressed vapor is then in the thermodynamic state known as a superheated vapor and it is at a temperature and pressure at which it can be condensed with either cooling water or cooling air. That hot vapor is routed through a condenser where it is cooled and condensed into a liquid by flowing through a coil or tubes with cool wa- ter or cool air flowing across the coil or tubes. This is where the circulating refrigerant rejects heat from the system and the rejected heat is carried away by either the water or the air (whichever may be the case). The condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve where it undergoes an abrupt reduction in pressure. That pressure reduction results in the adiabatic flash evaporation of a part of the liquid refrigerant. The auto-refrigeration effect of the adiabatic flash evaporation lowers the temperature of the liquid and vapor refrigerant mixture to

51 where it is colder than the temperature of the enclosed space to be refrigerated. The cold mixture is then routed through the coil or tubes in the evaporator. A fan circulates the warm air in the enclosed space across the coil or tubes carrying the cold refrigerant liquid and vapor mixture. That warm air evaporates the liquid part of the cold refrigerant mixture. At the same time, the circulating air is cooled and thus lowers the temperature of the enclosed space to the desired temperature. The evaporator is where the circulating refrigerant absorbs and removes heat which is subsequently rejected in the condenser and transferred elsewhere by the water or air used in the condenser. To complete the refrigeration cycle, the refrigerant vapor from the evaporator is again a saturated vapor and Repair & Maintenance of Window & Split AC is routed back into the compressor. Refrigerants \"Freon\" is a trade name for a family of haloalkane refrigerants manufactured by DuPont and other compa- nies. These refrigerants were commonly used due to their superior stability and safety properties: they were not flammable at room temperature and atmospheric pressure, nor obviously toxic as were the fluids they replaced, such as sulfur dioxide. Haloalkanes are also an order(s) of magnitude more expensive than petro- leum derived flammable alkanes of similar or better cooling performance. Unfortunately, chlorine- and fluo- rine-bearing refrigerants reach the upper atmosphere when they escape. In the stratosphere, CFCs break up due to UV radiation, releasing their chlorine free radicals. These chlorine free radicals act as catalysts in the breakdown of ozone through chain reactions. One CFC molecule can cause thousands of ozone molecules to break down. This causes severe damage to the ozone layer that shields the Earth's surface from the Sun's strong UV radiation, and has been shown to lead to increased rates of skin cancer. The chlorine will remain active as a catalyst until and unless it binds with another particle, forming a stable molecule. CFC refriger- ants in common but receding usage include R-11 and R-12. Newer refrigerants with reduced ozone deple- tion effect such as HCFCs (R-22, used in most homes today) and HFCs (R-134a, used in most cars) have re- placed most CFC use. HCFCs in turn are being phased out under the Montreal Protocol and replaced by hy- drofluorocarbons (HFCs), such as R-410A, which lack chlorine. However, CFCs, HCFCs, and HFCs all have large global warming potential.Shri Technologies Newer refrigerants are currently the subject of research, such as supercritical carbon dioxide, known as R- 744. These have similar efficiencies compared to existing CFC and HFC based compounds, and have many orders of magnitude lower global warming potential.

52 Shri TechnologiesShri Technologies Thermodynamic analysis of the system Temperature–Entropy diagram The thermodynamics of the vapor compression cy- cle can be analyzed on a temperature versus entropy diagram as depicted in Figure. At point 1 in the dia- gram, the circulating refrigerant enters the compres- sor as a saturated vapor. From point 1 to point 2, the vapor is isentropically compressed (i.e., compressed at constant entropy) and exits the compressor as a superheated vapor. From point 2 to point 3, the vapor travels through part of the condenser which removes the superheat by cooling the vapor. Between point 3 and point 4, the vapor travels through the remainder of the condenser and is condensed into a saturated liquid. The condensation process occurs at essentially constant pressure. Between points 4 and 5, the saturated liquid refrigerant passes through the expansion valve and undergoes an abrupt decrease of pressure. That process results in the adiabatic flash evaporation and auto-refrigeration of a portion of the liquid (typically, less than half of the liquid flashes). The adiabatic flash evaporation pro- cess is isenthalpic (i.e., occurs at constant enthalpy). Between points 5 and 1, the cold and partially vaporized refrigerant travels through the coil or tubes in the evaporator where it is totally vaporized by the warm air (from the space being refrigerated) that a fan circu- lates across the coil or tubes in the evaporator. The evaporator operates at essentially constant pressure and boils of all available liquid there after adding 4-8 deg kelvin of super heat to the refrigerant as a safeguard for the compressor as it cannot pump liquid. The resulting refrigerant vapor returns to the compressor inlet at point 1 to complete the thermodynamic cycle. It should be noted that the above discussion is based on the ideal vapor-compression refrigeration cycle which does not take into account real world items like frictional pressure drop in the system, slight internal irreversibility during the compression of the refrigerant vapor, or non-ideal gas behavior (if any). Types of gas compressors

Shri Technologies 53 Repair & Maintenance of Window & Split AC The most common compressors used in chillers are reciprocating, rotary screw, centrifugal, and scroll com- pressors. Each application prefers one or another due to size, noise, efficiency and pressure issues. Com- pressors are often described as being either open, hermetic, or semi-hermetic, to describe how the compres- sor and/or motor is situated in relation to the refrigerant being compressed. Variations of motor/ compressor types can lead to the following configurations:  Hermetic motor, hermetic compressor  Hermetic motor, semi-hermetic compressor  Open motor (belt driven or close coupled), hermetic compressor  Open motor (belt driven or close coupled), semi-hermetic compressor Typically in hermetic, and most semi-hermetic compressors (sometimes known as accessible hermetic com- pressors), the compressor and motor driving the compressor are integrated, and operate within the refrig- erant system. The motor is hermetic and is designed to operate, and be cooled by, the refrigerant being compressed. The obvious disadvantage of hermetic motor compressors is that the motor drive cannot be maintained in situ, and the entire compressor must be removed if a motor fails. A further disadvantage is that burnt out windings can contaminate whole refrigeration systems requiring the system to be entirely pumped down and the refrigerant replaced. An open compressor has a motor drive which is outside of the refrigeration system, and provides drive to the compressor by means of an input shaft with suitable gland seals. Open compressor motors are typically air-cooled and can be fairly easily exchanged or repaired without degassing of the refrigeration system. The disadvantage of this type of compressor is a failure of the shaft seals, leading to loss of refrigerant. Open motor compressors are generally easier to cool (using ambient air) and therefore tend to be simpler in design and more reliable, especially in high pressure applications where compressed gas temperatures can be very high. However the use of liquid injection for additional cooling can generally overcome this issue in most hermetic motor compressors. Questions 1. What is a vapour compression system 2. What is a compressor 3. What are the different types of compressors

54 Shri TechnologiesShri Technologies Simple Absorption Refrigeration System An absorption refrigerator is a refrigerator that uses a heat source (e.g., solar energy, a fossil-fueled flame, waste heat from factories, or district heating systems) which provides the energy needed to drive the cool- ing process. Absorption refrigerators are often used for food storage in recreational vehicles. The principle can also be used to air-condition buildings using the waste heat from a gas turbine or water heater. This use is very efficient, since the gas turbine then produces electricity, hot water, and air-conditioning (called cogenera- tion/trigeneration). The standard for the absorption refrigerator is given by the ANSI/AHRI standard 560-2000 History In the early years of the twentieth century, the vapor absorption cycle using water-ammonia systems was popular and widely used, but after the development of the vapor compression cycle it lost much of its im- portance because of its low coefficient of performance (about one fifth of that of the vapor compression cycle). Nowadays, the vapor absorption cycle is used only where waste heat is available or where heat is derived from solar collectors. Absorption refrigerators are a popular alternative to regular compressor refrigerators where electricity is unreliable, costly, or unavailable, where noise from the compressor is problematic, or where surplus heat is available (e.g., from turbine exhausts or industrial processes, or from solar plants). Absorption cooling was invented by the French scientist Ferdinand Carré in 1858. The original design used water and sulphuric acid. In 1922 Baltzar von Platen and Carl Munters, while they were still students at the Royal Institute of Tech- nology in Stockholm, Sweden, enhanced the principle with a 3-fluid configuration. This \"Platen-Munters\" design can operate without a pump. Commercial production began in 1923 by the newly formed company AB Arctic, which was bought by Electrolux in 1925. In the 1960s the absorption refrigeration saw a renaissance due to the substantial de- mand for refrigerators for caravans. AB Electrolux established a subsidiary in the U.S, named Dometic Sales Corporation. The company marketed refrigerators for RVs under the Dometic brand. In 2001 Electro- lux sold most of its leisure products line to the venture-capital company EQT which created Dometic as a stand-alone company.

Shri Technologies 55 Repair & Maintenance of Window & Split AC In 1926 Albert Einstein and his former student Leó Szilárd proposed an alternative design known as the Ein- stein refrigerator. At the 2007 TED Conference, Adam Grosser presented his research of a new, very small, \"intermittent ab- sorption\" vaccine refrigeration unit for use in third world countries. The refrigerator is a small unit placed over a campfire, that can later be used to cool 15 liters of water to just above freezing for 24 hours in a 30 de- gree Celsius environment. Principles Absorption cooling process Both absorption and compressor refrigerators use a refrigerant with a very low boiling point (less than 0 °F (−18 °C)). In both types, when this refrigerant evaporates (boils), it takes some heat away with it, providing the cooling effect. The main difference between the two systems is the way the refrigerant is changed from a gas back into a liquid so that the cycle can repeat. An absorption refrigerator changes the gas back into a liq- uid using a method that needs only heat, and has no moving parts other than the refrigerant itself. The absorption cooling cycle can be described in three phases: 1. Evaporation: A liquid refrigerant evaporates in a low partial pressure environment, thus extracting heat from its surroundings (e.g. the refrigerator's compartment). Due to the low pressure, the temperature need- ed for evaporation is also lower. 2. Absorption: The now gaseous refrigerant is absorbed by another liquid (e.g. a salt solution), reducing its partial pressure in the evaporator and allowing more refrigerant to evaporate.

56 Shri TechnologiesShri Technologies 3. Regeneration: The refrigerant-saturated liquid is heated, causing the refrigerant to evaporate out. This happens at a significantly higher pressure. The refrigerant is then condensed through a heat exchanger to replenish the supply of liquid refrigerant in the evaporator. In comparison, a compressor refrigerator uses an electrically powered compressor to increase the pressure on the gas, and then condenses the hot high pressure gas back to a liquid by heat exchange with a coolant (usually air). Once the high pressure gas has cooled and condensed into a liquid, it passes through an ori- fice which creates a pressure drop, which causes the liquid to evaporate. The evaporation process absorbs heat, and the temperature of the refrigerant drops to its boiling point at the now low pressure. Another difference between the two types is the refrigerant used. Compressor refrigerators typically use an HCFC or HFC, while absorption refrigerators typically use ammonia or water. Simple salt and water system A simple absorption refrigeration system common in large commercial plants uses a solution of lithium bromide salt and water. Water under low pressure is evaporated from the coils that are being chilled. The water is absorbed by a lithium bromide/water solution. The water is driven off the lithium bromide solu- tion using heat. Water spray absorption refrigeration Another variant, depicted to the right, uses air, water, and a salt water solution. The intake of warm, moist air is passed through a sprayed solution of salt water. The spray lowers the humidity but does not significantly change the temperature. The less humid, warm air is then passed through an evaporative cooler, consisting of a spray of fresh water, which cools and re-humidifies the air. Humidity is removed from the cooled air with anoth- er spray of salt solution, providing the outlet of cool, dry air. The salt solution is regenerated by heating it under low pressure, causing water to evaporate. The water evaporated from the salt solution is re-condensed, and rerouted back to the evaporative cooler.

57 Single pressure absorption refrigeration 1. Hydrogen enters the pipe with liquid ammonia (or lithium bromide solution) 2. Ammonia and hydrogen enter the inner com- partment of the refrigerator. An increase in volume causes a decrease in the partial pressure of the liq- uid ammonia. The ammonia evaporates, requiring energy to overcome the ΔHVap. The required ener- gy is drawn from the interior of the refrigerator, thus cooling it. 3. Ammonia and hydrogen return from the inner compartment, ammonia returns to absorber and dissolves in water. Hydrogen is free to rise up- wards. 4. Ammonia gas condensation (passive cooling). 5. Hot ammonia (gas). 6. Heat insulation and distillation of ammonia gas from water. 7. Heat source (electric). 8. Absorber vessel (water and ammonia solution). A single-pressure absorption refrigerator uses three substances: ammonia, hydrogen gas, and water. The Repair & Maintenance of Window & Split AC system is pressurized to the point where the ammonia is liquid (14-16atm). The cycle is closed, with all hy- drogen, water and ammonia collected and endlessly reused. The cooling cycle starts with liquefied ammonia entering the evaporator at room temperature. The evapo- rated ammonia is mixed with hydrogen. The partial pressure of the hydrogen gas is used to regulate the total pressure of the ammonia (liquid) and hydrogen (gas) solution, which in turn regulates the boiling point of the ammonia. As the ammonia boils in the evaporator, it requires energy to overcome the enthalpy of vaporization. This energy is drawn from the refrigerator's interior and provides the cooling required.Shri Technologies The next three steps exist to separate the gaseous ammonia and the hydrogen: 1. The ammonia (gas) and hydrogen (gas) solution flows through a pipe from the evaporator into the ab- sorber. In the absorber, the solution of gas flows into a solution of ammonia (liquid) and water (liquid). The

58 ammonia dissolves in the water allowing the gaseous hydrogen to collect at the top of the absorber, while the ammonia (liquid) and water (liquid) solution remains at the bottom. 2. The next step separates the ammonia and water. In the generator, heat is applied to the solution to dis- till the ammonia from the water. Some water vapor and bubbles remain mixed with the ammonia. This water is removed in the final separation step, by passing it through the separator, an uphill series of twist- ed pipes with minor obstacles to pop the bubbles, allowing the water vapor to condense and drain back to the generator. 3. Finally, the ammonia gas enters the condenser. In this heat exchanger, the hot ammonia gas transfers its energy to the ambient air allowing it to condense. This provides liquid ammonia, which flows down to be mixed with hydrogen gas, allowing the cycle to repeat. Questions 1. What is an absorption refrigerator 2. Water spray absorption refrigeration Shri TechnologiesShri Technologies

59 CompressorsShri Technologies The temperature of the evaporator coil can go from 33 degrees F Repair & Maintenance of Window & Split AC to 0 degrees F. If it goes below 32 degrees F, the moisture that's supposed to drain off the coils will freeze. This makes for a very (surprise!) in efficient system, so a thermostatic switch is used to connect and disconnect it to the compressor as necessary. Expansion Valve The expansion valve determines the correct amount of refriger- ant going into the evaporator, and it lowers the pressure of the refrigerant. When the compressor starts, the expansion valve opens and the liquid refrigerant flows through a strainer in the high pressure liquid inlet. Once in the expansion valve, the refrigerant is correctly pressur- ized. As the evaporator calls for more refrigerant, the expansion valve allows the required amount of low pressure liquid refrigerant into the coils. The expansion valve maintains the delicate balance between the heat load and the cooling efficiency of the evaporator. Discharge/Suction Service Valves Discharge and suction service valves allow the air conditioning system to be emptied and filled. These valves also provide places where the system can be checked with pressure gauges. Note: Some systems use a Schrader valve in place of the discharge and suction valves. This is a spring-loaded valve which looks rather like the valve in a tire. The Compressor Relay A capillary tube from a cycling switch lets the switch know what the temperature is in the evaporator. This switch turns the compressor on and off to keep the evaporator temperature at about 32 to 45 degrees F. The relay switch keeps moisture from freezing on the evaporator core. Electric Air Conditioning Fan Sometimes an extra electric fan is placed in front of the condenser to provide an extra flow of air during

60 Shri TechnologiesShri Technologies warm weather, or for times when the car has to idle for a long time. You activate and deactivate the air conditioning fan when you turn it on and off at the control panel. Compressor Belt The compressor is engine driven by a belt on the front of the crankshaft. The purpose of the compressor is to circulate the refrigerant in the system under pressure, this concentrates the heat it contains.  At the compressor, the low pressure gas is changed to high pressure gas.  This pressure buildup can only be accomplished by having a restriction in the high pressure side of the system. This is a small valve located in the expansion valve. The compressor has reed valves to control the entrance and exit of refrigerant gas during the pumping op- eration. These must be firmly seated.  An improperly seated intake reed valve can result in gas leaking back into the low side during the compression stroke, raising the low side pressure and impairing the cooling effect.  A badly seated discharge reed valve can allow condensing or head pressure to drop as it leaks past the valve, lowering the efficiency of the compressor. Two service valves are located near the compressor as an aid in servicing the system.  One services the high side, it is quickly identified by the smaller discharge hose routed to the conden- ser.  One is used for the low side, the low side comes from the evaporator, and is larger than the discharge hose The compressor is normally belt-driven from the engine crankshaft. Most manufacturers use a magnetic- type clutch which provides a means of stopping the pumping of the compressor when refrigeration is not desired. Compressor Relief Valve Some compressors have a relief valve for regulating pressure. If the system discharge pressure exceeds rat- ed pressure, the valve will open automatically and stay open until the pressure drops. The valve will then close automatically.

61 Compressor Noise Complaints Many noise complaints can be traced to the compressor mount and drive.  If a unit is noisy at one speed and quiet at another, it is not compressor noise.  Many times this kind of noise can be eliminated or greatly reduced by changing the belt adjustment.  Usually tightening mounts, adding idlers, or changing belt adjustment and length are more successful in removing or reducing this type of noise, than replacing the compressor.  Noises from the clutch are difficult to recognize because the clutch is so close to the compressor. A loose bolt holding the clutch to the shaft will make a lot of noise.  The difference, between suction pressure and discharge pressure, also plays an important part on sound level.  A compressor with low suction pressure will be more noisy than one with a higher pressure.  Consider whether the system is properly charged, whether the expansion valve is feeding properly to use the evaporator efficiently, and whether enough air is being fed over the evaporator coil. Questions 1. What is a compressor 2. Draw the diagram of a compressor and explain the parts 3. What are the types of compressorShri Technologies Repair & Maintenance of Window & Split AC

62 Shri TechnologiesShri Technologies Sealed (Hermetic) and semi sealed compressor Basically, a hermetic seal is one that is airtight. It is a common designator for systems that deal with gas compression and transmission. In such systems, hermeticity is a level specified for a particular test meth- od under specific conditions of usage. In compressors for refrigeration systems, the type of hermeticity is also described by the logistics of the system, in other words, the relationship of the compressor and motor drive in relation to the vapor or gas that is being compressed. Industry Designations Industry designates the various compression schemes as hermetically sealed or as semi-hermetic. In all cases of hermetic and most cases of semi-hermetic, the motor and compressor comprise an integrated unit, and operate within the pressurized gas environment of the system. In this way, the compressor unit and the gas form a symbiotic relationship. The unit compresses the gas and the gas cools the unit. Semi Versus Full Hermetic Seals The difference between semi-hermetic and hermetic compressors is that the latter is manufactured in a one-piece welded steel casing that is never intended to be opened. That means that any parts that fail within the compressor require that the entire compressor be replaced. In contrast, semi-hermetic compres- sors can be opened for repair. The main advantage of both types of compressors is that neither offers a leakage path for gas to escape to the outside world. Open Compressors Early models of refrigeration compressors were of the so-called open type, with the pistons and cylinders sealed within a crankcase, and a crankshaft extending through the body for an external power source. A shaft seal around the crankshaft prevented the loss of refrigerant and oil from the body. Although at one time open type compressors were widely used, they have many inherent disadvantages such as greater weight, higher cost, larger size, vulnerability to seal failures, difficult shaft alignment, ex- cessive noise, and short life of belts or direct drive components. As a result, the open type compressor has

63 been largely replaced with the accessible-hermetic and hermetic type motor-compressor in most applica- tions, and the use of open type compressors continues to decline except for specialized applications such as automobile air conditioning. The main advantage of open compressors is that they can be driven by sources other than electricity, such as a turbine or an internal combustion engine. However, they are sus- ceptible to leakage over time, particularly as the seals begin to age and degrade. Seals are often a thermo- plastic material, which must be kept lubricated in order to maintain the seal’s effectiveness. At regular in- tervals, these seals must be replaced. For this reason, an important part of compressor maintenance is a schedule that alerts technicians to replace the compressor seals. In this case, it behooves the technicians to have a ready source of 100% OEM compatible seals ready for installation.Shri Technologies Repair & Maintenance of Window & Split AC

64 Shri TechnologiesShri Technologies Performance of the compressor Positive displacement compressors all work on the same principle and have the same loss mechanisms. However, the relative magnitude of the different losses will be different in each type. For example, leak- age losses will be low in a lubricated reciprocating compressor with good piston rings, but may be signifi- cant in a dry screw unit, especially if the speed is low and the pressure increase, high. Cooling of the gas, which is beneficial, will be small in a reciprocating compressor, but may be almost complete in a liquid flooded screw compressor. All compressor types have a clearance volume that contains gas at the discharge pressure at the end of the discharge process. This volume may be small in some designs and significant in others. Some types, for example reciprocating compres-sors may have a large clearance volume, but recover the work done on this gas by expanding it back to suction pressure in the cylinder; other types, for examples crew compres- sors, let the gas in the clearance space expand back to suction pres-sure without recovering the work. Some compressor types, specifically those that use fixed ports for the discharge, are designed to operate at a fixed volume ratio. (For a given gas, this is equivalent to a fixed pressure ratio.) As the ratio varies from this value, the compressor effi- ciency will be less than the optimum. Other compressor types use either ports that can be varied with slides or they use pressure actuated valves. These types are optimized at any pressure ratio. Compressor Performance: The performance, that is the capacity (mass of gas compressed) and the power required to compress the gas, is affected by many details of the compressor’s design. Several of these are discussed below. They are discussed first with reference to a reciprocating compressor, and then with ref- erence to a screw compressor. The losses in other types of positive displacement compressors will be simi- lar to those discussed here. All types of compressors have losses caused by flow losses, by heat transfer, and by leakage from the high pressure to the low pressure zone and some types have losses associated with the valves Question 1. What is compressor performance

65 Oil & Lubricating System of CompressorShri Technologies LUBRICATION Repair & Maintenance of Window & Split AC An adequate supply of oil must be maintained in the crankcase at all times to insure continuous lubrica- tion. The normal oil level should be maintained at or slightly above the center of the sight class. On all Copelametic compressors 5 H.P. and larger in size, and on 3 H.P. “NR” models, compressor lubrication is provided by means of a positive displacement oil pump. The pump is mounted on the bearing housing, and is driven from a slot in the crankshaft into which the flat end of the oil pump drive shaft is fitted. Oil is forced through a hole in the crankshaft to the compressor bearings and connecting rods. A spring loaded ball check valve serves as a pressure relief device, allowing oil to bypass directly to the compressor crank- case if the oil pressure rises above its setting. Since the oil pump intake is connected directly to the com- pressor crankcase, the oil pump inlet pressure will always be crankcase pressure, and the oil pump outlet pressure will be the sum of crankcase pressure plus oil pump pressure. Therefore, the net oil pump pres- sure is always the pump outlet pressure minus the crankcase pressure. When the compressor is operating with the suction pressure in a vacuum, the crankcase pressure is negative and must be added to the pump outlet pressure to determine the net oil pump pressure A typical compound gauge is calibrated in inches of mercury for vacuum readings, and 2 inches of mercury are approximately equal to 1 psi. In normal operation, the net oil pressure will vary depending on the size of the compressor, the temperature and viscosity of the oil, and the amount of clearance in the compressor bearings. Net oil pressures of 30 to 40 psi are normal, but adequate lubrication will be maintained at pres- sures down to 10 psi. The bypass valve is set at the factory to prevent the net pump pressure from exceed- ing 60 psi. The oil pump may be operated in either direction, the reversing action being accomplished by a friction plate which shifts the inlet and outlet ports. After prolonged operation in one direction, wear, corrosion, varnish formation, or burrs may develop on the reversing plate, and this can prevent the pump from re- versing. Therefore, on installations where compressors have been in service for some time, care must be taken to maintain the original phasing of the motor if for any reason the electrical connections are dis- turbed.

66 The presence of liquid refrigerant in the crankcase can materially affect the operation of the oil pump. Vi- olent foaming on start up can result in the loss of oil from the crankcase, and a resulting loss of oil pres- sure until oil returns to the crankcase. If liquid refrigerant or a refrigerant rich mixture of oil and refriger- ant is drawn into the oil pump, the resulting flash gas may result in large variations and possibly a loss of oil pressure. Crankcase pressure may vary from suction pressure since liquid refrigerant in the crankcase can pressur- ize the crankcase for short intervals, and the oil pressure safety switch low pressure connection should always be connected to the crankcase. During a rapid pull-down of the refrigerant evaporating temperature, the amount of refrigerant in solu- tion in the crankcase oil will be reduced, and may cause flash gas at the oil pump. During this period the oil pump must pump both the flash gas and oil, and as a result the oil pressure may decrease temporarily. This will merely cause the oil pump to bypass less oil, and so long as the oil pressure remains above 9 psi, adequate lubrication Shri TechnologiesShri Technologies

67 CondensersShri Technologies a condenser is a device or unit used to condense a substance from its gaseous to its liquid state, typically Repair & Maintenance of Window & Split AC by cooling it. In so doing, the latent heat is given up by the substance, and will transfer to the condenser coolant. Condensers are typically heat exchangers which have various designs and come in many sizes ranging from rather small (hand-held) to very large industrial-scale units used in plant processes. For ex- ample, a refrigerator uses a condenser to get rid of heat extracted from the interior of the unit to the outside air. Condensers are used in air conditioning, industrial chemical processes such as distillation, steam pow- er plants and other heat-exchange systems. Use of cooling water or surrounding air as the coolant is com- mon in many condensers A condenser unit used in central air conditioning systems typically has a heat exchanger section to cool down and condense incoming refrigerant vapor into liquid, a compressor to raise the pressure of the refrigerant and move it along, and a fan for blowing outside air through the heat exchanger section to cool the refrigerant inside. A typical configuration of such a condenser unit is as follows: The heat ex- changer section wraps around the sides of the unit with the compressor inside. In this heat exchanger section, the refrigerant goes through multiple tube passes, which are surrounded by heat transfer fins through which cooling air can move from outside to inside the unit. There is a motorized fan inside the condenser unit near the top, which is covered by some grating to keep any objects from accidentally falling inside on the fan. The fan is used to blow the outside cooling air in through the heat exchange section at the sides and out the top through the grating. These condenser units are located on the out- side of the building they are trying to cool, with tubing between the unit and building, one for vapor refrigerant entering and another for liquid refrigerant leaving the unit. Of course, an electric power supply is needed for the compressor and fan inside the unit. Direct contact condenser In this type of condenser, vapors are poured into the liquid directly. The vapors lose their latent heat of va- porization; hence, vapors transfer their heat into liquid and the liquid becomes hot. In this type of conden- sation, the vapor and liquid are of same type of substance. In another type of direct contact condenser, cold water is sprayed into the vapour to be condensed.

68 Shri TechnologiesShri Technologies Refrigerant flow controllers, Hand expansion valve and capillary tube; Thermal Expansion valve. Automatic and Thermal Expansion Valve. High & Low side float and Solenoid valve Refrigerant flow control valves are used to ensure the refrigeration system is performed in accordance with the conditions as designed, particularly during partial load operation. All the valves have some un- desirable side effect such as line pressure drop, except it is required by design such as throttling valve. Therefore, when making valve selection, it is im- portant to select a valve that is producing less pressure drop. All the valves must be checked if it is designed and constructed for refrigeration du- ty. Every valve used for the refrigeration system must serve the purpose and the duty as designat- ed, regardless if it is manual valve or automatic control valve. Manual stop valves are for the pur- pose of providing the conveniences of services and maintenances. Manual valves also include the check valves and hand expansion. Typical hand ex- pansion valve is shown in Figure 1. Manual expansion valve or needle valve is used as a throttling orifice in application wherever is re- quired. All the valves used for system performance control or for system safety should be fully automatic. The common use automatic valves and its function are described as the following: Solenoid Valve: Solenoid valve is an electrical control on - off valve. It is for the automatic control of refrigerant flow for either vapor or liquid line; the valve can be either normally open or normally closed. The electrical power supply can be either 220 or 110 or even 24 volts. Thermostatic Expansion Valve: Thermostatic expansion valve is also referred to as direct expansion (DX) or dry expansion valve. The DX valve is used as the automatic control throttling valve for DX evaporator. DX valve has two important ele- ments as shown in Figure one is the external bulb which is to allow enough refrigerant flow for the refrig-

69 eration capacity requirement and the other element is the ex- ternal equalization line which is to restrict the refrigerant flow just enough to provide a 10 to 15 ̊F superheat at the outlet of the heat exchanger. Low Pressure Float Valve: Low pressure float valve is a throttling expansion device. It provides a seal between -the high side and the low side; it controls the refrigerant flow from the high side to the low side intercooler or flooded type heat exchanger, and to maintain a desired liquid level in that vessel. Figure is the cross section of the low pressure float valve. The assembly consists of the float ball, the body and the valve.Shri Technologies Three-Way Valve Refrigeration System Repair & Maintenance of Window & Split AC  Three-Way Valves  Located in discharge line downstream from vibrasorber  In cool operation, directs refrigerant into condenser  In heat/defrost mode hot gas is directed to the evaporator  Three-way valve is controlled by the pilot solenoid, an electrically operated valve used only during the heat or defrost mode Three-Way Valve Operation  Operates on principles of spring pressure and differential refrigerant pressure

70 Shri TechnologiesShri Technologies  In cool mode valve is spring holds spool valve against back side of valve  Spool valve seat blocks flow to the evaporator leaving the condenser side open  Pilot solenoid is de-energized blocking three-way valve end cap from suction side of compressor  High-pressure hot gas from compressor flows through bleed passage to both sides of the spool valve equalizing the pressure  In heat/defrost mode pilot solenoid is energized and opens right side of spool valve piston to suction side of system  Refrigerant from the bleed passage is drawn into the suction side of the compressor  Discharge pressure on left side of spool valve piston overcomes the spring pressure and suction pres- sure on right side of spool valve piston, piston shifts to the right  Spool valve blocks flow of refrigerant to condenser and path to evaporator Solenoid Valve Check Valves  Used by most manufactures of refrigeration equipment  Allows refrigerant flow in one direction but stops in the op- posite direction  Two styles used, serviceable and non-serviceable  Serviceable type use a removable cap for access to the seal and spring  Serviceable type usually made of brass  Non-serviceable are inline used to minimize leaks  Refrigerant Flow Three-Way Valve System (Thermo King Units) Cooling Cycle  Hot gas leaves compressor through vibrasorber the discharge service valve  Hot gas flows through three-way valve to the condenser

Shri Technologies 71 Repair & Maintenance of Window & Split AC  As super heated gas flows through the conden- ser it changes states to a sub cooled liquid  Sub cooled liquid flows through the check valve  Liquid is stored in the receiver  Refrigerant Flow Three-Way Valve System (Thermo King Units)  Refrigerant flows through liquid line to the fil- ter dryer  Refrigerant flow through the heat exchanger where it gives up heat to cold suction line  Liquid then passes through the TXV where is metered through the distributor tubes to the evaporator  The pressure drop across the TXV causes the refrigerant to boil and absorb heat from the controlled space  Refrigerant Flow Three-Way Valve System (Thermo King Units)  Cold refrigerant passes through heat exchanger and absorbs more heat  Refrigerant then passes through receiver, liquid is separated before suction vibrasorber and service valves and through suction throttling valve  Last refrigerant passes through compressor to start cycle over  Three-Way Valve System Operating in Cool Mode  Refrigerant Flow Three-Way Valve System (Thermo King Units) Heat Cycle  Hot gas leaves compressor through vibrasorber the discharge service valve  Hot gas moves through the discharge vibrasorber and three-way valve  Pilot solenoid is energized, three-way valve is shifted to the heat position stopping flow to condenser and opening flow to drip pan and evaporator  Heat from evaporator is blow into cargo space heating the controlled space  Refrigerant Flow Three-Way Valve System (Thermo King Units)  If in the defrost mode a damper door solenoid is energized blocking off air flow to controlled space. Ice melts and coil dries but controlled space stays cool.  Cool vapor along with some liquid pass through to the heat exchanger to accumulator. Liquid is sepa- rated and vapor returns to compressor.

72 Shri TechnologiesShri Technologies  The accumulator may be heated to aid in vaporization liquid refrigerant. Refrigerant Flow Three-Way Valve System (Thermo King Units)  High pressure refrigerant is teed off at the drip pan to the bass pass check valve at the receiver tank  The condenser check valve is held closed blocking the condenser, refrigerant in the receiver can only exit through the tank outlet valve  Liquid refrigerate passes through the drier and passes through a notch in seat or internal orifice of TXV  Refrigerant mixes with hot gas in distributor  Refrigerant once trapped in receiver is now used in heat defrost cycle allowing compressor to achieve higher pressures thereby more heat  Three-Way Valve System Operating in Heat Mode  Refrigerant Flow Three-Way Valve System (Thermo King Units) Defrost Cycle  Flow in defrost cycle is identical to heat cycle  In defrost cycle air is not cycled through the loaded area  Closing damper door traps heat in evaporator compartment  Heat builds up melting ice, water drips into defrost pans to a pair of drain tubes  When trailer box temperatures become very low, melted water can freeze in pan  Defrost pan heaters are coils that hot gas pass through to defrost the drip pans  Most units will not defrost until evaporator reaches 45 degrees F and will terminate at 55 degrees F NOTE It is harmful to the cargo to have warm air circulated through temperature sensitive products that are required to keep frozen or refrigerated. For this reason, if a problem is detected with the defroster door (not closing), it must be replaced immediately because the unit will not come out of heat/defrost cycle until the whole trailer has warmed up far above the set point.  Operation of Solenoid Control System (Carrier) Cool Mode  In cool mode, SV3 and SV4 are closed, SV1 and SV2 are open  Refrigerant flows from compressor through discharge check valve to condenser, changes state from gas to liquid  Liquid passes through SV1 which is normally open

Shri Technologies 73 Repair & Maintenance of Window & Split AC  Liquid then flow through the receiver where excess liquid is stored  Liquid then flows out king valve and into the sub-cooler which is another portion of the condenser  Operation of Solenoid Control System (Carrier)  Exiting the sub-cooler refrigerant pass through the dryer and SV2, which is normally closed  Refrigerant flows through the TXV which meters flow to controls a constant superheat at evaporator outlet  The pressure drop caused by the TXV causes the refrigerant to boil in the evaporator and absorb heat from the controlled space  Quench valve, a small TXV senses the compressor discharge, if unsafe pressures are sensed it will allow small amounts of liquid refrigerant into suction line, it boils off in pressure drop and cools the compres- sor  Solenoid Controlled System Operating in Cool Mode  Operation of Solenoid Control System (Carrier) Heating Cycle  Hot vapor leaves compressor through discharge service valves, discharge vibrasorber through dis- charge check valve  Refrigerant flows to SV3 and SV4, these valves are initially closed when placed in heat mode  SV4 will energize and allow refrigerant to pass

74 Shri TechnologiesShri Technologies  60 seconds after SV4 is energized if temperature and pressure requirements are met SV3 will be ener- gized  Operation of Solenoid Control System (Carrier)  Once SV3 and SV4 open hot gas will flow directly into the evaporator  SV1, normally open, will energize and close stopping refrigerant flow through the condenser  Hot gas flows through the bypass check valve filling the receiver, subcooler, filter dryer and is stopped at SV2  SV2 is normally closed and is controlled by HP2 When in heat/defrost mode  SV2 is cycled open and closed by HP2 to allow refrigerant to flow to the evaporator  Operation of Solenoid Control System (Carrier)  Excess refrigerant trapped in receiver is needed for heat/defrost cycle  Teed into TXV feed line is a quench valve  Quench valve, a small TXV senses the compressor discharge, if unsafe pressures are sensed it will al- low small amounts of liquid refrigerant into suction line, it boils off in pressure drop and cools the compressor  The superheated refrigerant that get gets past SV3 and SV4 enter the evaporator and transfer heat to

75 Repair & Maintenance of Window & Split AC the evaporator coils to heat the cargo space  Operation of Solenoid Control System (Carrier)  The transfer of heat from refrigerant and suction of compressor cause the pressure to drop with a corre- sponding drop in the boiling temperature of the refrigerant  Because of the drop in pressure the refrigerant does not condense  Refrigerant leaves the evaporator and enters suction line, through the suction vibrasorber and into the suction side of compressor  The cycle then repeats itself  Solenoid Controlled System Operating in Heat/Defrost Mode  Four way Valve Operation Cooling Cycle  Refrigerant leaves compressor through service valve and vibrasorber and flows to the four-way valve  Pilot solenoid (cool) is energized opening a passage o the suction side  Differential pressure causes valve to shift left opening passage to the condenser side of four way valve  Refrigerant enters the condenser to give up heat to ambient air  Refrigerant the flow to the drier, heat exchanger and liquid line check valve  Four way Valve Operation Cooling Cycle  Refrigerant then enters the TXV, distributor tubes and metered into the evaporator  The pressure causes refrigerate to boil and absorb heat in the cargo space  Refrigerant passes through heat exchanger, four-way valve then enters the accumulator  Refrigerant exits the accumulator and return to the compressor through the suction line and suction vibrasorber  A check valve with orifice prevent refrigerant from entering the drip tray during a cool cycle  Four-Way Operation Cool CycleShri Technologies

76 Shri Technologies  Four-Way Operation Heat Cycle  In heat cycle four-way reversing valve is shifted to change operation of the evaporator and condenser  The condenser becomes the evaporator absorbing heat from ambient air  In cold environments shutters may have to be held shut in order to boil refrigerant  Super-heated refrigerant leaves compressor through discharge service valve and discharge vibrasorb- er to four-way  Four-Way Operation Heat Cycle  Pilot solenoid (heat) is energized opening passage to suction side of compressor  Differential pressure case valve to shift right opening passage to evaporator  Refrigerant flows through heat exchanger then into the evaporator which is now acting as a condenser  Heat is given up to air passing through evaporator coil  Some of the refrigerant passes through the drip pan, the check valve, and orifice, entering condenser as a low-pressure saturated mixture  Four-Way Operation Heat Cycle  A check valve in the cool line prevents refrigerant through heat exchanger and dryer  Liquid refrigerant passes through expansion valve (heat) at inlet of condenser, through the check valve, then enters the condenser  The refrigerant changes state by absorbing heat from ambient air  The low pressure vapor return to four-way valve, through accumulator and back to suction side of compressorShri Technologies

77 Evaporator in both Window & Split ACShri Technologies The evaporator works the opposite of the condenser, here refrigerant liquid is converted to gas, absorbing Repair & Maintenance of Window & Split AC heat from the air in the compartment. When the liquid refrigerant reaches the evaporator its pressure has been reduced, dissipating its heat con- tent and making it much cooler than the fan air flowing around it. This causes the refrigerant to absorb heat from the warm air and reach its low boiling point rapidly. The refrigerant then vaporizes, absorbing the maximum amount of heat. This heat is then carried by the refrigerant from the evaporator as a low-pressure gas through a hose or line to the low side of the compressor, where the whole refrigeration cycle is repeated. The evaporator removes heat from the area that is to be cooled. The desired temperature of cooling of the area will determine if refrigeration or air con-ditioning is desired. For example, food preservation generally requires low refrigeration temperatures, ranging from 40°F (4°C) to below 0°F (-18°C). A higher temperature is required for human comfort. A larger area is cooled, which requires that large vol- umes of air be passed through the evaporator coil for heat exchange. A blower becomes a necessary part of the evaporator in the air conditioning system. The blower fans must not only draw heat-laden air into the evaporator, but must also force this air over the evaporator fins and coils where it surrenders its heat to the refrigerant and then forces the cooled air out of the evaporator into the space being cooled. Fan Speeds Fan speed is essential to the evaporation process in the system. Heat exchange, as we explained under con- denser operation, depends upon a temperature differential of the air and the refrigerant. The greater the differential, the greater the amount of heat exchanged between the air and the refrigerant. A high heat load, as is generally encountered when the system is turned on, will allow rapid heat transfer between the air and the cooler refrigerant. A blower fan turned on to its highest speed will deliver the most air across the fins and coils for rapid evap- oration.

78 Shri Technologies For the coldest air temperature from the evaporator, operate the blower fan at the lowest speed so the heat will be absorbed by the refrigerant from the air Problems of Flooded or Starved Evaporator Coils Changing the state of the refrigerant in the evaporator coils is as important as the air flow over the coils. Liquid refrigerant supplied to the coils by the expansion valve expands to a vapor as it absorbs heat from the air. Some liquid refrigerant must be supplied throughout the total length of the evaporator coils for full capacity. A starved evaporator coil is a condition in which not enough refrigerant has been supplied through the to- tal coil length. Therefore, expansion of the refrigerant has not occurred through the whole coil length, re- sulting in poor coil operation and too-low heat exchange. A flooded evaporator is the opposite of the starved coil. Too much refrigerant is passed through the evapo- rator coils, resulting in unexpanded liquid passing onto the suction line and into the compressor. Questions 1. What is fan Speed 2. What are the Problems of Flooded or Starved Evaporator CoilsShri Technologies

Shri Technologies 79 Repair & Maintenance of Window & Split AC Receiver A common accessory used on many refrigeration systems is the liquid receiver. It is basically a storage ves- sel designed to hold excess refrigerant not in circulation. Refrigeration systems exposed to varying heat loads, or systems utilizing a condenser flooding valve to maintain a minimum head pressure during low ambient temperatures, will need a receiver to store excess refrigerant. Liquid receivers are installed in the liquid line as close as possible to the outlet of the condenser. The piping between the condenser and the receiver should be arranged to allow free drainage. The piping should also not cause excessive friction pressure loss or gas binding and must have adequately sized valves and connec- tion fittings. The location of the receiver should not cause excessive heat to be added to the refrigerant, such as from di- rect solar radiation when located outdoors or near building heating equipment when installed indoors. Ex- cess heat added to a receiver will reduce the operating efficiency of the system. However, if the receiver is installed outdoors and the system is required to operate during low ambient temperatures, it may be neces- sary to install trace heaters to maintain adequate pressure in the receiver in order to avoid system problems at startup. Considering Capacity A receiver’s storage capacity is based on 80 percent of its internal volume at a refrigerant temperature of 90° F per ARI Standard 495. Generally, a receiver is selected to hold 90 percent of the total system charge to pro- vide adequate reservoir during high loads and to allow the refrigerant to be isolated between the condenser and the receiver during repairs. A receiver generally has a service valve installed at its outlet, typically referred to as the king valve. A re- ceiver will sometimes also have a service valve at its inlet. The king valve is very useful for service techni- cians as it allows them to read the system’s pressure at the receiver and is the valve used to trap the system’s refrigerant charge in the condenser and receiver during repairs. A receiver may also have some type of relief valve installed, such as a fusible plug, ruptured disc, or a pres- sure relief valve. This provides the controlled release of abnormally high pressure within the receiver before that pressure causes an uncontrolled eruption of the refrigerant from the receiver or another part of the sys- tem.

80 A common question asked when discussing receivers is, “How can the refrigerant leave the receiver in a subcooled state?” That answer is because in the receiver, there is both liquid and vapor refrigerant. By defi- nition, that refers to a saturated refrigerant. So, is the refrigerant in the receiver saturated or subcooled? The answer to this question is, both. At the liq- uid vapor interface — where the liquid and vapor are in contact — the refrigerant is saturated, but the re- frigerant below the interface can exist at a lower temperature. And, since the refrigerant’s pressure is con- stant, the refrigerant below the interface is subcooled. Normally, the refrigerant leaving the receiver is picked up below the interface toward the bottom of the receiver, allowing the refrigerant to leave in a sub- cooled state. Shri TechnologiesShri Technologies

81 Accessories of Refrigeration SystemShri Technologies The Parts of an Air Conditioner Repair & Maintenance of Window & Split AC Let's get some housekeeping topics out of the way be- fore we tackle the unique components that make up a standard air conditioner. The biggest job an air condi- tioner has to do is to cool the indoor air. That's not all it does, though. Air conditioners monitor and regulate the air temperature via a thermostat. They also have an onboard filter that removes airborne particulates from the circulating air. Air conditioners function as dehumidifiers. Because temperature is a key compo- nent of relative humidity, reducing the temperature of a volume of humid air causes it to release a portion of its moisture. That's why there are drains and moisture -collecting pans near or attached to air conditioners, and why air conditioners discharge water when they operate on humid days. Still, the major parts of an air conditioner manage refrigerant and move air in two directions: indoors and outside:  Evaporator - Receives the liquid refrigerant  Condenser - Facilitates heat transfer  Expansion valve - regulates refrigerant flow into the evaporator  Compressor - A pump that pressurizes refrigerant The cold side of an air conditioner contains the evaporator and a fan that blows air over the chilled coils and into the room. The hot side contains the compressor, condenser and another fan to vent hot air coming off the compressed refrigerant to the outdoors. In between the two sets of coils, there's an expansion valve. It regulates the amount of compressed liquid refrigerant moving into the evaporator. Once in the evaporator, the refrigerant experiences a pressure drop, expands and changes back into a gas. The compressor is actual- ly a large electric pump that pressurizes the refrigerant gas as part of the process of turning it back into a

82 Shri TechnologiesShri Technologies liquid. There are some additional sensors, timers and valves, but the evaporator, compressor, condenser and expansion valve are the main components of an air conditioner. Although this is a conventional setup for an air conditioner, there are a couple of variations you should know about. Window air conditioners have all these components mounted into a relatively small metal box that installs into a window opening. The hot air vents from the back of the unit, while the condenser coils and a fan cool and re-circulate indoor air. Bigger air conditioners work a little differently: Central air conditioners share a control thermostat with a home's heating system, and the compressor and condenser, the hot side of the unit, isn't even in the house. It's in a separate all-weather housing outdoors. In very large buildings, like hotels and hospitals, the exterior condensing unit is often mounted somewhere on the roof. A few moments spent reading this will help you understand our diagnosis of Air Conditioner. 1. COMPRESSOR: Compresses the refrigerant from a low temperature, low pressure gas to a high tem- perature, high-pressure gas. 2. CONDENSER: Is actually a radiator in which the refrigerant condenses from a gas to a liquid form as it is cooled. 3. ORIFICE TUBE / EXPANSION VALVE: Regulates the liquid refrigerant going into the bottom of the evaporator. Actually acts as a restrictor to the flow of the liquid refrigerant. 4. EVAPORATOR: This is where the refrigerant evaporates from a liquid form back into a gaseous form. As the refrigerant evaporates it gets very cold and allows the cars interior to be cooled off. 5. ACCUMULATOR / DRIER: A storage tank and filter for the freon. Its main purpose is to remove moisture from the refrigerant. 6. REFRIGERANT: More commonly known as freon is the liquid or gas which passes through all the other components in the A/C System. 7. CHARGE PORT / SCHRADER VALVE: The valve where refrigerant is put into the system and sys- tem pressures are checked. 8. COMPRESSOR CLUTCH: Engages and disengages the compressor. 9. REFRIGERANT OIL: The system lubricant. 10. HOSE ASSEMBLY: A combination of rubber and steel or aluminum pipes through which the freon passes between the other major components. 11. CYCLING SWITCH: Regulates the operation of the compressor depending on system pressures or temperatures. 12.CONTROL PANEL: Where you select the temperature, quantity and location of air to come from the heater/ air conditioning system.

83 Refrigerants (CFC & Non CFC refrigerants) and Refrigerants CylinderShri Technologies A refrigerant is a substance or mixture, usually a fluid, used in a heat pump and refrigeration cycle. In Repair & Maintenance of Window & Split AC most cycles it undergoes phase transitions from a liquid to a gas and back again. Many working fluids have been used for such purposes. Fluorocarbons, especially chlorofluorocarbons, became commonplace in the 20th century, but they are being phased out because of their ozone depletion effects. Other common refrig- erants used in various applications are ammonia, sulfur dioxide, and non-halogenated hydrocarbons such as propane. The ideal refrigerant would have favorable thermodynamic properties, be noncorrosive to mechanical com- ponents, and be safe, including free from toxicity and flammability. It would not cause ozone depletion or climate change. Since different fluids have the desired traits in different degree, choice is a matter of trade- off. The desired thermodynamic properties are a boiling point somewhat below the target temperature, a high heat of vaporization, a moderate density in liquid form, a relatively high density in gaseous form, and a high critical temperature. Since boiling point and gas density are affected by pressure, refrigerants may be made more suitable for a particular application by choice of operating pressures. History: Early mechanical refrigeration systems employed sulfur dioxide, methyl chloride and ammonia. Being tox- ic, sulfur dioxide and methyl chloride rapidly disappeared from the market with the introduction of CFCs. Occasionally, one may encounter older machines with methyl formate, chloromethane, or dichloromethane (called carrene in the trade). Chlorofluorocarbons were little used for refriger- ation until better synthesis methods, developed in the 1950s, reduced their cost. Their domination of the market was called into question in the 1980s by concerns about depletion of the ozone layer.

84 Shri TechnologiesShri Technologies Following legislative regulations on ozone depleting chlorofluorocarbons (CFCs) and hydrochlorofluoro- carbons (HCFCs), substances used as substitute refrigerants such as perfluorocarbons (FCs) and hydro- fluorocarbons (HFCs) have also come under criticism. They are currently subject to prohibition discus- sions on account of their harmful effect on the climate. In 1997, FCs and HFCs were included in the Kyoto Protocol to the Framework Convention on Climate Change. In 2006, the EU adopted a Regulation on fluorinated greenhouse gases, which makes stipulations regarding the use of FCs and HFCs with the in- tention of reducing their emissions. The provisions do not affect climate-neutral refrigerants. Uses: Refrigerants such as ammonia (R717), carbon dioxide and non-halogenated hydrocarbons do not deplete the ozone layer and have no (ammonia) or only a low (carbon dioxide, hydrocarbons) global warming potential. They are used in air-conditioning systems for buildings, in sport and leisure facilities, in the chemical/pharmaceutical industry, in the automotive industry and above all in the food industry (production, storage, retailing). In these settings their toxicity is less a concern than in home equipment. Emissions from automobile air conditioning are a growing concern because of their impact on climate change. From 2011 on, the European Union will phase out refrigerants with a global warming potential (GWP) of more than 150 in automotive air conditioning (GWP = 100 year warming potential of one kilo- gram of a gas relative to one kilogram of CO2). This will ban potent greenhouse gases such as the refriger- ant HFC-134a—which has a GWP of 1410—to promote safe and energy-efficient refrigerants. One of the most promising alternatives is CO2 (R-744). Carbon dioxide is non-flammable, non-ozone de- pleting, has a global warming potential of 1. R-744 can be used as a working fluid in climate control sys- tems for cars, residential air conditioning, hot water pumps, commercial refrigeration, and vending ma- chines. R12 is compatible with mineral oil, while R134a is compatible with synthetic oil that contains es- ters. GM has announced that it will start using \"hydrofluoroolefin\", HFO-1234yf, in all of its brands by 2013. Dimethyl ether (DME) is also gaining popularity as a refrigerant, but like propane, it is also danger- ously flammable. Some refrigerants are seeing rising use as recreational drugs, leading to an extremely dangerous phenom- enon known as inhalant abuse. Questions 1. List a few CFC Refrigerants 2. List a few Non-CFC Refrigerants 3. What is inhalant abuse

85 Greenhouse effectShri Technologies The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by at- Repair & Maintenance of Window & Split AC mospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back to- wards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases. Solar radiation at the frequencies of visible light largely passes through the atmosphere to warm the plane- tary surface, which then emits this energy at the lower frequencies of infrared thermal radiation. Infrared radiation is absorbed by greenhouse gases, which in turn re-radiate much of the energy to the surface and lower atmosphere. The mechanism is named after the effect of solar radiation passing through glass and warming a greenhouse, but the way it retains heat is fundamentally different as a greenhouse works by reducing airflow, isolating the warm air inside the structure so that heat is not lost by convection. If an ideal thermally conductive blackbody were the same distance from the Sun as the Earth is, it would have a temperature of about 5.3 °C. However, since the Earth reflects about 30% of the incoming sunlight, this idealized planet's effective temperature (the temperature of a blackbody that would emit the same amount of radiation) would be about −18 °C. The surface temperature of this hypothetical planet is 33 °C below Earth's actual surface temperature of approximately 14 °C. The mechanism that produces this differ- ence between the actual surface temperature and the effective temperature is due to the atmosphere and is known as the greenhouse effect. Earth’s natural greenhouse effect makes life as we know it possible. However, human activities, primarily the burning of fossil fuels and clearing of forests, have intensified the natural greenhouse effect, causing global warming. The inert nature of many halons, chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFC), with the benefits of their being nonflammable and nontoxic, made them good choices as refrigerants, but their stability in the atmosphere and their corresponding global warming potential and ozone depletion poten- tial raised concerns about their usage. In order from the highest to the lowest potential of ozone depletion are Bromochlorofluorocarbon, CFC then HCFC. Though HFC and PFC are non-ozone depleting, many have global warming potentials that are thousands of times greater than CO2. Some other refrigerants such as propane and ammonia are not inert, and are flammable or toxic if released.

86 New refrigerants were developed in the early 21st century that are safer for the environment, but their appli- cation has been held up due to concerns over toxicity and flammability. Shri TechnologiesShri Technologies

87 Basic Electricity; Current, Voltage, Resistance measuring Basic electricity: Electricity is the flow of electrons from one place to another. Electrons can flow through any material, but does so more easily in some than in others. How easily it flows is called resistance. The resistance of a mate- rial is measured in Ohms. Matter can be broken down into:Shri Technologies  Conductors: electrons flow easily. Low resistance. Repair & Maintenance of Window & Split AC  Semi-conductors: electron can be made to flow under certain circumstances. Variable resistance accord- ing to formulation and circuit conditions.  Insulator: electrons flow with great difficulty. High resistance. Since electrons are very small, as a practical matter they are usually measured in very large numbers. A Coulomb is 6.24 x 1018 electrons. However, electricians are mostly interested in electrons in motion. The flow of electrons is called current, and is measured in AMPS. One amp is equal to a flow of one coulomb per second through a wire. Making electrons flow through a resistance requires an attractive force to pull them. This force, called Elec- tro-Motive Force or EMF, is measured in volts. A Volt is the force required to push 1 Amp through 1 Ohm of resistance. As electrons flow through a resistance, it performs a certain amount of work. It may be in the form of heat or a magnetic field or motion, but it does something. This work is called Power, and is measured in Watts. One Watt is equal to the work performed by 1 Amp pushed by 1 Volt through a resistance. An electric circuit is formed when a conductive path is created to allow free electrons to continuously move. This continuous movement of free electrons through the conductors of a circuit is called a current, and it is often referred to in terms of \"flow,\" just like the flow of a liquid through a hollow pipe. The force motivating electrons to \"flow\" in a circuit is called voltage. Voltage is a specific measure of poten- tial energy that is always relative between two points. When we speak of a certain amount of voltage being present in a circuit, we are referring to the measurement of how much potential energy exists to move elec-

88 Shri TechnologiesShri Technologies trons from one particular point in that circuit to another particular point. Without reference to two particu- lar points, the term \"voltage\" has no meaning. Free electrons tend to move through conductors with some degree of friction, or opposition to motion. This opposition to motion is more properly called resistance. The amount of current in a circuit depends on the amount of voltage available to motivate the electrons, and also the amount of resistance in the circuit to op- pose electron flow. Just like voltage, resistance is a quantity relative between two points. For this reason, the quantities of voltage and resistance are often stated as being \"between\" or \"across\" two points in a circuit. To be able to make meaningful statements about these quantities in circuits, we need to be able to describe their quantities in the same way that we might quantify mass, temperature, volume, length, or any other kind of physical quantity. For mass we might use the units of \"kilogram\" or \"gram.\" For temperature we might use degrees Fahrenheit or degrees Celsius. Here are the standard units of measurement for electrical current, voltage, and resistance: The \"symbol\" given for each quantity is the standard alphabetical letter used to represent that quantity in an algebraic equation. Standardized letters like these are common in the disciplines of physics and engineer- ing, and are internationally recognized. The \"unit abbreviation\" for each quantity represents the alphabeti- cal symbol used as a shorthand notation for its particular unit of measurement. And, yes, that strange- looking \"horseshoe\" symbol is the capital Greek letter Ω, just a character in a foreign alphabet (apologies to any Greek readers here). Each unit of measurement is named after a famous experimenter in electricity: The amp after the French- man Andre M. Ampere, the volt after the Italian Alessandro Volta, and the ohm after the German Georg Simon Ohm. The mathematical symbol for each quantity is meaningful as well. The \"R\" for resistance and the \"V\" for voltage are both self-explanatory, whereas \"I\" for current seems a bit weird. The \"I\" is thought to have been meant to represent \"Intensity\" (of electron flow), and the other symbol for voltage, \"E,\" stands for

89 \"Electromotive force.\" From what research I've been able to do, there seems to be some dispute over the meaning of \"I.\" The symbols \"E\" and \"V\" are interchangeable for the most part, although some texts re- serve \"E\" to represent voltage across a source (such as a battery or generator) and \"V\" to represent voltage across anything else. All of these symbols are expressed using capital letters, except in cases where a quantity (especially volt- age or current) is described in terms of a brief period of time (called an \"instantaneous\" value). For exam- ple, the voltage of a battery, which is stable over a long period of time, will be symbolized with a capital letter \"E,\" while the voltage peak of a lightning strike at the very instant it hits a power line would most likely be symbolized with a lower-case letter \"e\" (or lower-case \"v\") to designate that value as being at a single moment in time. This same lower-case convention holds true for current as well, the lower-case let- ter \"i\" representing current at some instant in time. Most direct-current (DC) measurements, however, be- ing stable over time, will be symbolized with capital letters.Shri Technologies Repair & Maintenance of Window & Split AC

90 Shri TechnologiesShri Technologies Safety Precaution in Electricity  Avoid contact with energized electrical circuits. Please don’t make fun of this rule if you already know this (and you probably already know if you are read- ing these lines) and remember that if something bad occurs – you probably won’t have second chance. That’s not funny. Treat all electrical devices as if they are live or energized. You never know. Disconnect the power source before servicing or repairing electrical equipment.  The only way to be sure. Use only tools and equipment with non-conducting handles when working on electrical devices.  Easy to check. Never use metallic pencils or rulers, or wear rings or metal watchbands when working with electrical equipment. This rule is very easy to forget, especially when you are showing some electrical part pointing with metallic pencil. When it is necessary to handle equipment that is plugged in, be sure hands are dry and, when possible, wear nonconductive gloves, protective clothes and shoes with insulated soles. If it is safe to do so, work with only one hand, keeping the other hand at your side or in your pocket, away from all conductive material. This precaution reduces the likelihood of accidents that result in current pass- ing through the chest cavity. If you ever read about current passing through human body you will know, so remember – work with one hand only. Minimize the use of electrical equipment in cold rooms or other areas where condensation is likely. If equip- ment must be used in such areas, mount the equipment on a wall or vertical panel. If water or a chemical is spilled onto equipment, shut off power at the main switch or circuit breaker and unplug the equipment. Very logical. NEVER try to remove water or similar from equipment while energized. Afterall, it’s stupid to do so.

91 If an individual comes in contact with a live electrical conductor, do not touch the equipment, cord or per- son. Disconnect the power source from the circuit breaker or pull out the plug using a leather belt. Tricky situation, and you must be very calm in order not to make the situation even worse. Like in previous rules – Always disconnect the power FIRST.Shri Technologies Repair & Maintenance of Window & Split AC

92 Shri Technologies Electrical; wiring diagram and Earthlings. (Open circuit, Short Circuit, Earth test- ing) Electrical wiring connections inside The Window air conditioning units Here we are interested on how the main power cord is connected inside the unit and this can be explained as follow A- Inside the unit the main power cord is split to: 1. The ground wire (either green or a bare wire) is screwed to the metal casing of the unit. 2. Hot wire 3. Neutral wire. B- Hot wire goes to the selector switch on a window unit to feed power to the vital parts, compressor and fan motor as follows:  Hot wire to selector switch to thermostat switch to compressor  Hot wire to selector switch to fan motor. C- Neutral wire will be connected to fan motor and com- pressor without goes through any switch. These connections are made on the wire connector in the back of the selector switch so, all neutral wires are common to each other be- cause they are connected to the same point.Shri Technologies

93 Some examples for the complete electrical wiring diagrams for Window Air Conditioning Unit areShri Technologies Repair & Maintenance of Window & Split AC

94 Shri TechnologiesShri Technologies We can find examples for the com- plete wiring diagrams for Window Air Conditioning Unit which be mounted on the unit casing. also, you can find examples for the complete wiring diagrams for Window Air Conditioning Unit, touch and remote control type in Figure The power flow inside a Typical Window air conditioning unit in the cooling mode

Shri Technologies 95 Repair & Maintenance of Window & Split AC  When you turn the selector switch to cool mode, the power that came in from the cord that connected to the selector via hot wire goes to the fan so the fan operates.  The selector switch also sends the power via hot wire to the compressor, but the compressor will not operate until the thermostat comes to the on position, then the compressor will operates and the cooling cycle begin. Electrical diagram of Split AC Unit The split systems are individual systems in which the two heat exchangers are separated (one outside, one inside). There are two main parts of the split air conditioner which are: 1. Outdoor unit, 2. Indoor unit. 1- Outdoor unit: This unit is installed outside the room or office space which is to be cooled and houses important compo- nents of the air conditioner like:  The compressor,  Condenser Cooling Fan,  Expansion Valve.