2 Learning ObjectivesDescribe the purpose of the compressor, condenser, metering valve, and evaporator.Explain the construction of the compressor, condenser, metering valve, and evaporator.Illustrate the operation of service valves and Schrader valves.Describe the purpose and construction of a vibrasorber.
3 Learning Objectives (continued) Demonstrate the operation of a thermostatic expansion valve.Explain the superheat setting of the TXV.Describe the mounting location of a sensing bulb.Determine the superheat setting of the TXV.Explain the purpose of the distributor.Describe the purpose of the receiver tank.
4 Learning Objectives (continued) Compare the drier materials and explain the purpose of the filter dryer.Describe the purpose and operation of the heat exchangerDescribe the purpose and operation of the accumulator.Explain the purpose of pressure regulating devices.Describe the purpose and operation of the different types of refrigerant safety valves.
5 The Four Basic Component The CompressorThe CondenserThe Metering DeviceThe EvaporatorRefrigerant, the fifth basic component
7 The CompressorPumps refrigerant through the systemPressurizes the vapor refrigerantRaises the temperature of the refrigerantDraws a very low suction pressureHigh discharge and low suction pressures help control the boiling of the refrigerant
8 Compressor OperationRefrigerant passes through suction throttling valve (if equipped) into compressor crankcase.Piston moves down cylinder, refrigerant is drawn in through suction reed valve.Piston moves upward, refrigerant compresses to 50:1 ratio.Compressed vapor exits through the discharge valve plate to discharge manifold.
10 Service ValvesLocated on compressor suction and discharge portsAllows service manifold connectionCan isolate the compressor for service or repairsBack seated- isolates service portMid seat- opens service portsFront seat- isolates compressor from system
12 CAUTIONCare must be taken to NEVER front seat the discharge service valve while the compressor is operating. Even thought the high pressure cut-out switch might be positioned below the valve, it would not operate fast enough to prevent major damage to the compressor and prevent possible personal injury.
14 Vibrasorbers Flexible suction and discharge lines Positioned at the compressorPrevent engine and compressor vibrations from reaching the copper piping of the refrigerant systemThere are two types of vibrasorbersTypical discharge vibrasorbers are made up of bellows shaped stainless steel center and a covering of braided stainless steel wireTypical suction vibrasorber made up of reinforced fabric covered hoses, often using replaceable mechanical fittings
16 CondenserLocated outside of controlled spaceReleases heat from controlled space to outside airConsists of copper tubing running through aluminum cooling finsRefrigerant changes state from a high pressure hot vapor to high pressure cooler liquid
18 Receiver TankActs as storage tank for refrigerantUsually contains one or two sight glassesUsually have inlet and outlet service valveRefrigerant can be isolated between receiver and compressor for downstream service
20 Filter DryerFilters and dries refrigerantLocated in liquid line between receiver outlet and TXVMay be between compressor and condenserMay be between evaporator and compressorThree different materials commonly usedSilica GelActivated AluminaMolecular Sieve
23 Heat ExchangerLocated in liquid line between receiver and TXV or outlet of evaporatorTwo important functions:Subcools liquid refrigerant before TXVEvaporates any liquid refrigerant before it reaches the compressor
27 Thermal Expansion Valve Operation Sensing bulb pressure applied to one side of the diaphragm tries to open valve against spring pressure.Evaporator outlet or compressor suction pressure applied to the opposite side of the diaphragm helps to make the valve responsive to compressor suction pressure.Spring pressure, which is applied to the needle assembly and diaphragm on the evaporator side, constantly tries to close the valve.
28 Determining Superheat Determine the suction pressure at the compressor suction service valve.Using a refrigerant pressure temperature chart, determine the saturation temperature at the observed pressure.Measure the temperature of the suction gas at the evaporator outlet.Subtract the saturated temperature read from the chart in Step 2 from the temperature measured in Step 3. The difference between the two is the superheat of the suction gas returning to the compressor.
29 TXV Sensing BulbTXV sensing bulb regulates the flow of refrigerant to the evaporatorBulb is normally filled with same refrigerant used in the systemCharge can be vapor or liquidSome are designed to control the maximum opening pressure of the TXV to prevent compressor sluggingSensing bulb must have good mechanical connection with the evaporator outlet
30 TXV Sensing Bulb (continued) Sensing bulb must be positioned on the suction line so it can monitor actual vapor or line temperature, follow manufacturers recommendationsIf mounted at 6 o’clock, refrigerant oil can provided insulation from true vapor temperatureIf mounted at 12 o’clock bulb would be in direct contact with line possibly causing incorrect sensing of vapor temperature
31 Distributor TubeDistributor and header are located between the TXV outlet and evaporator inletDivides the refrigerant flow into several routes to the evaporator for greater efficiencyEquipped with a passage so that during the heating and defrost cycle, hot gas is pumped into the evaporator, bypassing the TXV
32 Evaporator Receives boiling refrigerant from the distributor As refrigerant boils it absorbs heat through the cooling fins which cools the air as it passes through themRefrigerant boils because of the pressure of the refrigerant is significantly lowered by the TXVMoist air can freeze on the fins reducing efficiency, a defrost cycle is needed to prevent thisMost evaporators are constructed of copper tubing swedged into aluminum fins.Tubing configuration and number of tubes determine the BTU rating of evaporator
34 AccumulatorSeparates liquid refrigerant from vaporous refrigerant before entering the compressorWhen system is operating intermittently or as heat pump, large quantities of liquid refrigerant can pass through suction line and enter the compressorLiquid refrigerant can cause broken pistons, bent connecting rods, broken valves, blown head gaskets, and damaged bearingsAccumulator normally has the capacity to hold the entire refrigerant charge to prevent compressor damage
36 Accumulator Operation Liquid and vapor enter accumulator and drop to the bottomVapor returns through “U” shaped tube to compressorAs vapor passes “U” tube it picks up liquid refrigerant and oil through metering hole in bottom of “U” tubeTo prevent to much liquid refrigerant from returning to compressor an anti-siphon hole is placed at the top of the “U” tubeTo aid in the evaporation process of the accumulator a device to heat the shell of the may be added
37 Evaporator Pressure Regulator Evaporator pressure regulator controls evaporator pressure regardless of compressor suction pressureThe pressure setting is that which is equal to 30 to 32 degrees Fahrenheit inside the evaporator coilOil by pass line between the base of the evaporator to the compressor suction is requiredThis type of valve not used in many application because many cargos require the evaporator to reach very low pressures in order to obtain low box temperatures
38 Suction Pressure Regulator Designed to limit crankcase suction pressure during heat and defrost cycle or startupDuring startup when evaporator and crankcase pressures are high, valve is closedWhen the crankcase internal suction pressure is below the set point of the valve, it begins to open and lower evaporator pressureAs the pressure of the evaporator is lowered the valve setting, it opens still more
39 Suction Pressure Regulator (continued) During defrost/heat cycle high pressure vapor is pumped from compressor to the distributor and evaporator, suction pressure rises.High pressure overcomes spring pressure in the valve and closes the inlet cutting off inlet flow of refrigerantThe restriction caused by the valve provides needed restriction for compressor to pump against during heat/defrost cycle
40 Suction Pressure Regulator (continued) This process causes compressor to pump high-pressure (temperature) refrigerant to evaporator for heating/defrost cycleSuction pressure regulators do not totally restrict refrigerant flow, they do not require oil bypass lineThese valves are adjustable by increasing or decrease spring pressure
42 Safety ValvesMost refrigeration units with more than 1 pound of refrigerant are equipped with a pressure relieving safety devicePrevent possible explosion by relieving pressure caused by fire, coil blockage, or overheating of unit2 types currently used, spring loaded and fusible metal plugSpring loaded type has spring loaded piston that excessive refrigerant pressure must overcome and vent through an exhaust port passage
43 Safety Valves (continued) Piston type may have slight refrigerant leak after venting but should reseal itselfFusible metal plug work on temperature only, usually 200 to 22 degree Fahrenheit or about 415 to 450 psiThe core material is designed to melt away, allowing refrigerant to escapeOnce a fusible plug releases pressure they must be replaced
45 SummaryThere are four main components used in a refrigeration systemThere are many other components that improve the efficiency of the system but not necessaryFrom the compressor superheated refrigerant passes service valves through the vibrasorberVibrasorbers isolates system from vibration caused by engine and compressor
46 Summary (continued)Refrigerant then enters the condenser and gives up heat to ambient airRefrigerant cools in the condenser and condenses from gas to liquidLiquid refrigerant then enters the receiver where it is stored until neededRefrigerant leaves receiver and passes through the filter dryer which removes moisture and contaminantsRefrigerant enters the heat exchanger which further removes heat from liquid refrigerant
47 Summary (continued)Refrigerant enters TXV and is metered to the distributor and then evaporatorTXV balances inlet flow to outlet temperature and pressure of refrigerant so it all has time to change state from liquid to a gas before exiting evaporatorRefrigerant then enters the accumulator if system is equippedAccumulator separates vapor to prevent liquid from entering the compressor
48 Summary (continued)Refrigerant flows from accumulator through suction line, through suction vibrasorber, through suction service valve, then through suction pressure regulator if equippedRegulator controls the load placed on the engine or electric motorRefrigerant flows out suction pressure regulator into suction side of compressorThe refrigerant is then compressed and starts the journey again