Service Training Meeting Guide 745 SERV1745-01 May 2003 TECHNICAL PRESENTATION AIR CONDITIONING PRINCIPLES AND OPERATIONS AIR CONDITIONING PRINCIPLES AND OPERATIONS MEETING GUIDE 745 SLIDES AND SCRIPT AUDIENCE Level I and II - Service personnel who understand the basic hydraulic principles and the fundamentals of electrical systems. CONTENT This presentation states the natural principles for removing heat, describes the operation of the air conditioning system components and discusses air conditioning service procedures. OBJECTIVES After learning the information in this presentation, the serviceman will be able to: 1. state the natural principles for removing heat, 2. locate and identify the components in the three air conditioning systems; 3. explain the operation of each component in the three air conditioning systems; and 4. trace the flow of refrigerant through the three air conditioning systems. REFERENCES Air Conditioning Principles and Operations Air Conditioning Service Procedures Air Conditioning and Heating R-134a, All Caterpillar Machines, Service Manual SERV2580-01 SERV2581-01 SENR5664 PREREQUISITES Interactive Video Course "Fundamentals of Mobile Hydraulics" Interactive Video Course "Fundamentals of Electrical Systems" TEMV9001 TEMV9002 Estimated Time: 2 Hours Visuals: 57 Visuals Serviceman Handouts: 7 line drawings Form: SERV1745 Date: 5/03 © 2003 Caterpillar Inc. STMG 745 5/03 -3- TABLE OF CONTENTS INTRODUCTION ..................................................................................................................5 AIR CONDITIONING PRINCIPLES....................................................................................7 Heat Transfer.....................................................................................................................7 Measurement of Heat........................................................................................................9 Sensible Heat...................................................................................................................11 Latent Heat......................................................................................................................12 Latent Heat of Fusion and Latent Heat of Vaporization .................................................14 Effects of Pressure ..........................................................................................................16 REFRIGERANT HFC-134A ................................................................................................20 BASIC AIR CONDITIONING SYSTEM............................................................................21 AIR CONDITIONING SYSTEMS AND COMPONENTS ................................................24 Orifice Tube System .......................................................................................................24 Compressor .....................................................................................................................26 Condenser .......................................................................................................................28 In-line Dryer and Orifice Tube .......................................................................................30 Evaporator and Blower Fan ............................................................................................32 Accumulator....................................................................................................................33 Thermostatic Expansion Valve System...........................................................................34 Thermostatic Expansion Valve .......................................................................................36 Receiver-dryer.................................................................................................................38 "H" Block Expansion Valve System ...............................................................................39 "H" Block Expansion Valve............................................................................................41 Thermostatic Switch .......................................................................................................42 Compressor Clutch..........................................................................................................44 Low Pressure Switch.......................................................................................................45 High Pressure Relief Valve .............................................................................................46 Pressure Switch Locations for Orifice Tube System.......................................................47 Pressure Switch Locations for "H" Block Expansion Valve system...............................48 Moisture Indicator...........................................................................................................49 WARNINGS .........................................................................................................................50 AIR CONDITIONING PERFORMANCE TESTS ..............................................................52 Visual Inspection, Engine Off.........................................................................................52 Operation Inspection, Engine On....................................................................................57 STMG 745 5/03 -4- TABLE OF CONTENTS (continued) AIR CONDITIONING SERVICE TOOLS MANIFOLD GAUGE SET.............................58 Schrader Valves...............................................................................................................59 Service Hose....................................................................................................................60 Performance Test.............................................................................................................61 Adding Refrigerant..........................................................................................................62 High Side-Low Side Temperatures ................................................................................63 Ambient Temperature vs. Barometric Pressure...............................................................64 Refrigerant Tanks............................................................................................................65 Air Conditioner Service Tools ........................................................................................66 Electronic Leak Detector ................................................................................................67 Recover, Evacuate and Charge Unit ...............................................................................68 Vacuum Pump .................................................................................................................69 Refrigerant Charging Scales ...........................................................................................70 Refrigerant Analyzer.......................................................................................................71 Air Conditioning Component Flusher ............................................................................72 CONCLUSION.....................................................................................................................73 SLIDE LIST..........................................................................................................................74 SERVICEMAN’S HANDOUTS ..........................................................................................75 STMG 745 5/03 -5- ORIFICE TUBE SYSTEM CONDENSER COIL COMPRESSOR INLINE DRYER CONDENSER FAN ACCUMULATOR EVAPORATOR COIL EVAPORATOR BLOWER FAN High Pressure Gas Low Pressure Gas High Pressure Gas/Liquid Mix Low Pressure Gas/Liquid Mix High Pressure Liquid Low Pressure Liquid 1 INTRODUCTION: • Removing heat This module will discuss the natural principles for removing heat as applied to the operation of vehicle air conditioning systems. • Basic air conditioning system Basic vehicle air conditioning system components and component functions are explained as they relate to the operation of the air conditioning system. The procedures for inspecting and servicing the air conditioning system are also covered. Basic safety practices will also be covered. The contents of this module should be treated as general information for air conditioning systems in all Caterpillar machines. STMG 745 5/03 • Presentation colors -6- The color codes for refrigerant used throughout this presentation are as follows: Red - High pressure liquid Purple - Low pressure liquid Red and White Stripes - High Pressure gas/liquid Mix Purple and White Stripes - Low Pressure gas/liquid Mix Red Cross Hatch - High pressure gas Purple Cross Hatch - Low pressure gas Green or Green Dots - Refrigerant oil STMG 745 5/03 -7- EVAPORATOR COIL 2 AIR CONDITIONING PRINCIPLES • Heat transfer Heat transfer Many know what air conditioning does, but very few understand how it works. An air conditioner evaporator, surprisingly enough, works similarly to a pot of boiling water on a stove. In fact, the reason why an air conditioner can continue to cool the air is because a liquid called the refrigerant is boiling within the evaporator coil. Or course, everyone knows a boiling pot is "hot" and an air conditioner is "cold." A cold substance that boils is usually quite confusing. • Condition cold Cold is thought to be a definite condition. Actually, the condition regarded as "cold" does not exist. Cold can only be defined in a negative way by saying "cold" is the absence of "heat." When heat is removed from a substance, it becomes cold as a result. Both the pot of boiling water and the air conditioner are simply devices for removing heat. STMG 745 5/03 -8- 3 • Heat flow The basis of all air conditioning systems is that heat flows from a warmer object to a cooler object. All substances contain some heat. Theoretically, the lowest temperature obtainable is 459° below 0°F (no one has reached that temperature). Anything warmer than 459° below 0°F contains heat. When making an object cold, the heat in the object being made cold is transferred to another object. Like water, which always flows downhill, heat always flows from a warm object to a colder object. Three ways in which heat is transferred are: • Conduction - Conduction, heat travel through a solid object. • Convection - Convection, heat travel through a substance such as water, steam or air. • Radiation - Radiation, when the increase in the temperature of a substance allows a measurable amount of heat to escape. STMG 745 5/03 -9- 4 Measurement of Heat • Heat measurement Heat is measured by intensity and by quantity. Place a pot of water over a flame on a stove. The water gets hotter and hotter until the water boils. A thermometer in the water shows the temperature. The thermometer tells the intensity of heat, not the quantity of heat present. • BTU The unit for measuring quantity of heat is called a British Thermal Unit, sometimes abbreviated to BTU. One BTU is specified as that amount of heat necessary to raise 1 pound of water 1°F (473.6 ml of water 0.55°C). STMG 745 5/03 - 10 - 5 • Quantity of heat The quantity of heat can best be explained by thinking of heat as drops of red coloring dye. Each drop of dye corresponds to 1 BTU. If one drop of red dye is added to a cup of water, the water will turn slightly pink. Two drops will turn the water reddish in color. Adding more drops will turn the water succeedingly deeper shades of red. Correspondingly, adding more BTU's to the water increases the temperature. STMG 745 5/03 0°C (32°F) WATER - 11 - + 180 BTU'S = 100°C (212°F) WATER (189.9 kJ) 6 Sensible heat • Types of heat Two types of heat also exist: sensible heat and latent heat. • Sensible heat Heat that is measured with a thermometer is called "sensible heat." Sensible heat can also be felt. Another explanation for sensible heat is the amount of heat needed to raise 1 pound of water from 0°C (32°F) to 100°C (212°F). STMG 745 5/03 - 12 - 0°C (32°F) 0°C (32°F) 7 Latent heat • Latent heat The second type of heat is called "latent heat." Latent heat is hidden heat. ("Latent" is the Latin word for hidden.) Latent heat cannot be felt nor can latent heat be measured with a thermometer. Latent heat can best be explained by inserting a thermometer into a block of ice. The thermometer reads 0°C (32°F). Allow the block of ice to melt and collect the melting water in a container. When the block of ice is checked a few hours later, the block of ice is smaller because some has melted away. However, the thermometer reads 0°C (32°F). Where did the heat go that caused the ice to melt? Some thought the added heat was in the water that melted from the ice. However, checking the water temperature as the water melts from the ice shows the water temperature to be only slightly higher than the temperature of the ice. STMG 745 5/03 • Latent heat used up - 13 - The slight increase in the water temperature does not account for all the heat the ice has absorbed. The only answer left is that the latent heat has been used up to change the ice from a solid to a liquid. All solids soak up huge amounts of heat when changing from a solid to a liquid. STMG 745 5/03 - 14 - 100°C (212°F) 0°C (32°F) 8 Latent Heat of Fusion and Latent Heat of Vaporization • Change water to ice Water changes into ice or ice changes into water at 0°C (32°F) sensible heat. The process of changing ice into water or water into ice is called "latent heat of fusion." 144 BTU's of latent heat is added to change 1 pound of ice into 1 pound of water. Therefore, the ice must absorb 144 BTU's of latent heat. To change 1 pound of water into 1 pound of ice, 144 BTU's of latent heat is removed from the water. • Change steam to water Water changes into steam or steam changes into water at 100°C (212°F). The process of changing water into steam or steam into water is called "latent heat of vaporization." 970 BTU's of latent heat is added to change 1 pound of water into steam. Therefore, 970 BTU's of latent heat is absorbed into 1 pound of water before all of the water is turned into steam. STMG 745 5/03 - 15 - Just as all solids soak up huge amounts of heat when changing to a liquid, liquids soak up huge amounts of heat when changing to a gas. • Boiling point • Increased flames Put some water in a pot, place a mercury thermometer in the water, and place the pot over a flame. As the water heats, the thermometer reading will rise. At atmospheric pressure, the water boils when the thermometer reaches 100°C (212°F) sensible heat. Increase the flame and the water will boil faster. However, the thermometer reading will not increase above 100°C (212°F). What happens to the additional heat from the increased flame? The additional heat is used to change the water from a liquid to a gas. Since the temperature of the boiling water does not increase above 100°C (212°F), the boiling must be a natural means for the water to cool itself. - 16 - ER E AT M OS PH STMG 745 5/03 EARTH OCEAN 9 Effects of Pressure • Atmospheric pressure As previously stated, at atmospheric pressure, water boils at 100°C (212°F). What is atmospheric pressure? • 14.7 psi Atmospheric pressure can be defined as "the weight of the atmosphere upon an object." Pressure, regardless of how it is produced, is measured in pounds per square inch (psi). At sea level, atmospheric pressure is 14.7 psi. Any pressure less than sea level (14.7 psi) is known as a "partial vacuum" or commonly called a "vacuum." Vacuum is measured in inches of mercury (in. Hg). A perfect vacuum (0 psi) has never been produced. No one has been able to mechanically obtain ZERO pressure. • Vacuum STMG 745 5/03 - 17 - 128 kPa (18.5 PSI) 101 kPa (14.7 PSI) 102.8°C (217°F) 100°C (212°F) 80 kPa (11.7 PSI) 60.5°C (141°F) 10 • Direct relationship • Normal pressure • Increase pressure • Decrease pressure There is a direct relationship between a liquid’s boiling point and the pressure on the liquid’s surface. Shown are three pots of boiling water. The pot on the left has a pressure of 14.7 psi and the water boils at 100°C (212°F). Increasing the pressure inside the pot causes the water to boil at a higher temperature. Decreasing the pressure inside the pot (creating a vacuum) causes the water to boil at a lower temperature. The pressure can be decreased (a vacuum created) to a point where the water boils without the flame. STMG 745 5/03 - 18 - VAPOR COMPRESSION 80°F 84 PSI 132°F 134 PSI 32°F 30 PSI 11 • Temperature pressure There is a direct relationship between the temperature of a vapor and the amount of pressure on the vapor. When the pressure on the vapor is increased, the temperature of the vapor also increases. STMG 745 5/03 - 19 - GAUGE MANIFOLD 0 WATER VACUUM PUMP 12 • Direct relationship There is a direct relationship between a vacuum, the ambient temperature, and the boiling point of a liquid. • Manifold gauge set Shown is a manifold gauge set connected to a vacuum pump and a flask with water. The vacuum pump lowers the pressure in the flask thus creating a vacuum. At a room temperature of 21°C (70°F), water boils with a vacuum of 28.2 in.Hg. (.13.8 psi). • Vacuum pump • Flask • Boiling water Boiling water is a natural cooling process. The boiling water removes the same amount of latent heat when boiling at 21°C (70°F) as when boiling at 100°C (212°F). Substances other than water react in the same manner but at different temperatures. STMG 745 5/03 - 20 - KEEP UPRIGHT DO NOT HEAT KEEP AWAY FROM FLAME WEAR SAFETY GLASSES DO NOT FREEZE DO NOT DROP R-134a DANGER WEAR GLOVES WHEN HANDLING 13 REFRIGERANT HFC-134A • Refrigerant • Refrigerant character • R134a The substance used in air conditioning systems is called "refrigerant." Many refrigerants are available. In fact, any liquid that will boil at temperatures near the freezing point of water can be used as a refrigerant. However, a good refrigerant should be non-poisonous and non-explosive to be safe. Also, a good refrigerant should be non-corrosive, odorless and mix well with oil. The refrigerant that is used in current Mobile Air Conditioning Systems is known as "Refrigerant HFC-134a." HFC-134a is made from Hydrogenated Fluorocarbons. HFC-134a has the same advantages of R12 but HFC-134a will not harm the atmosphere. STMG 745 5/03 - 21 - HFC-134a 14 BASIC AIR CONDITIONING SYSTEM • R134a boiling point Shown is an open flask of Refrigerant-HFC-134a at room temperature. The open flask represents the evaporator in an air conditioning system. When at atmospheric pressure (14.7 psi), HFC-134a boils at -27°C (-16°F). The heat in the room causes the refrigerant to boil. As the refrigerant boils, heat is drawn away from the surrounding area. The absence of heat makes the surrounding area cooler. However, such a system is not economical nor is it good for the atmosphere. STMG 745 5/03 - 22 - COMPRESSOR LOW PRESSURE HIGH PRESSURE 15 • Add compressor and high pressure flask Continue to build the basic air conditioning system by adding a compressor and a high pressure flask. The high pressure flask serves the same function as the condenser in a basic air conditioning system. Cork both flasks to prevent the refrigerant from escaping. • Liquid boils As the liquid refrigerant boils in the low pressure flask, the vapor is drawn through a hose into the compressor. The compressor increases the pressure of the vapor and the intensity of the heat. Since temperature is a measurement of the heat intensity, the temperature of the vapor increases. The high pressure, high temperature vapor flows into the high pressure flask. The temperature of the high pressure vapor is higher than the temperature of the surrounding area. Therefore, heat flows from the high pressure vapor to the surrounding area. The high pressure vapor cools and changes into a high pressure liquid. • High pressure vapor STMG 745 5/03 - 23 - COMPRESSOR ORIFICE LOW PRESSURE HIGH PRESSURE 16 • Add hose and orifice Complete the system by adding a hose to connect the flask of high pressure liquid to the flask of low pressure liquid. An orifice is inserted in the hose to maintain a pressure difference between the high pressure liquid and the low pressure liquid. • Low pressure When the flask of low pressure liquid refrigerant boils, the boiling process collects heat from the surrounding area. The low pressure refrigerant vapor is drawn through a hose into the compressor. The compressor raises the pressure and temperature of the vapor and stores it in the high pressure flask. The high pressure, high temperature vapor gives up heat to the cooler surrounding area, causing the high pressure vapor to cool and condense into a high pressure liquid. The high pressure liquid refrigerant flows through a hose and orifice to the flask for low pressure liquid refrigerant. The low pressure liquid refrigerant boils and repeats the cycle. • High pressure STMG 745 5/03 - 24 - ORIFICE TUBE SYSTEM CONDENSER COIL COMPRESSOR INLINE DRYER CONDENSER FAN ACCUMULATOR EVAPORATOR COIL EVAPORATOR BLOWER FAN High Pressure Gas Low Pressure Gas High Pressure Gas/Liquid Mix Low Pressure Gas/Liquid Mix High Pressure Liquid Low Pressure Liquid 17 AIR CONDITIONING SYSTEMS AND COMPONENTS Orifice Tube System • Orifice tube system The standard air conditioning system contains five basic components. The orifice tube system contains the following six components: Compressor - Increases pressure and temperature of refrigerant vapor Condenser - Removes the heat from the high pressure high temperature refrigerant vapor causing the vapor to change into high pressure liquid refrigerant In-line dryer Orifice Tube - Contains the desiccant and the orifice tube. Quick disconnects allow the in-line dryer to be easily changed when needed Evaporator - Low pressure liquid refrigerant boils, collecting heat from the surrounding area • Compressor • Condenser • In-line dryer Orifice Tube • Evaporator STMG 745 5/03 - 25 - - Acts as a liquid/vapor separator and ensures that only vapor will reach the compressor • Accumulator Accumulator • Orifice tube system On the orifice tube system, the liquid refrigerant leaving the evaporator can damage the compressor. Therefore, an accumulator is located in the suction line after the evaporator. The accumulator acts as a liquid/vapor separator and ensures that only vapor will reach the compressor. • Separator • Orifice tube •In-line dryer On some orifice tube systems, the orifice tube is located in the low pressure liquid line to the evaporator and the desiccant is in the accumulator. On systems with an in-line dryer, the desiccant is in the dryer. STMG 745 5/03 - 26 - COMPRESSOR INTAKE PASSAGE EXHAUST PASSAGE INTAKE PASSAGE EXHAUST PASSAGE EXHAUST VALVE INTAKE VALVE EXHAUST VALVE INTAKE VALVE COMPRESSION STROKE INTAKE STROKE 18 Compressor • Purpose of compressor The dual purpose of the compressor is: - Increase the temperature and pressure of refrigerant gas from the evaporator - Circulate the refrigerant throughout the system. • Reed valves The compressor has reed valves to control the entrance and exit of refrigerant gas during the pumping operation. • Piston movement As the piston moves downward in the bore, the suction reed or intake valve opens and the discharge reed or exhaust valve closes. The low pressure, heat laden refrigerant gas is drawn from the evaporator into the compressor. As the piston moves upward in the bore, the compressor pressurizes the gas, thus increasing the intensity of the heat. STMG 745 5/03 - 27 - • Heat intensity Since temperature is a measurement of heat intensity, the temperature of the gas increases. The high pressure, high temperature gas closes the suction reed valve or intake valve and opens the discharge reed valve or exhaust valve. The gas is forced through a hose to the condenser. • High side restriction The pressure increase is accomplished by adding a restriction in the high pressure side of the system. The restriction is caused by the orifice tube. The orifice tube is explained later in this presentation. STMG 745 5/03 - 28 - CONDENSER FROM COMPRESSOR TO INLINE DRYER 19 Condenser • Condenser purpose The purpose of the condenser is to transfer the heat in the refrigerant gas to the atmosphere and convert the refrigerant gas into a liquid. High pressure, high temperature refrigerant gas flows from the compressor into the condenser. As the hot, high pressure gas flows through the condenser, heat flows from the hot gas to the cooler air flowing through the condenser coils. The high pressure refrigerant gas cools and condenses into high pressure liquid. The high pressure liquid flows from the condenser to the in-line dryer. Two basic types of condensers are commonly used: • Ram air • Forced air Ram Air - Used in automotive applications Forced Air - Used on construction equipment. The ram air condenser depends on machine movement to force large volumes of air through the condenser coils. STMG 745 5/03 • Fans - 29 - The forced air condenser uses fans to move large volumes of air through the condenser coils. The air is cooler than the refrigerant gas inside the condenser. Heat flows from the hot refrigerant gas to the cooler air. STMG 745 5/03 - 30 - QUICK DISCONNECT OUTLET DESICCANT ORIFICE TUBE ASSEMBLY QUICK DISCONNECT INLET MOISTURE INDICATOR O-RING IN-LINE DRYER TUBE SCREEN BODY SCREEN TABS 20 In-line Dryer and Orifice Tube • In-line dryer The in-line dryer contains a desiccant bag and two quick disconnects. The disconnects allows the in-line dryer to be changed without reclaiming the refrigerant. Some in-line dryers may have a moisture indicator. • Orifice tube On most orifice tube systems, the orifice tube is installed in the in-line dryer. The older orifice tubes consist of a small tube through the center of a plastic body, two o-rings, two screens and two tabs. Note: The newer orifice tubes have only one o-ring. • Two screens • Low side • High side The two screens (one on each end) filter the refrigerant that flows through the small tube. The two o-rings are positioned to seal against leakage past the outside of the orifice tube. The two tabs engage the tooling when installing and removing the orifice tube. The orifice tube separates the A/C System high side from the low side. High pressure liquid refrigerant enters the orifice tube and low pressure liquid refrigerant exits the orifice tube. STMG 745 5/03 • Fixed diameter - 31 - The orifice tube has a fixed diameter and does not have the regulating capability of the expansion valve. The refrigerant flows from the orifice tube to the evaporator. The amount of liquid refrigerant entering the evaporator is usually more than the evaporator can boil off, therefore, some refrigerant will leave the evaporator in the liquid form. On some orifice tube systems, the orifice tube is installed in the evaporator inlet line. STMG 745 5/03 - 32 - EVAPORATOR FROM ORIFICE TUBE TO COMPRESSOR BLOWER FAN 21 Evaporator and Blower Fan • Evaporator unit The purpose of the evaporator and blower fan is to transfer the heat in the operator's compartment to the refrigerant in the air conditioner. • Blower fan The blower fan draws heat laden air from the operator's compartment over the evaporator fins and coils where the air surrenders heat to the refrigerant. • Low pressure liquid When the low pressure liquid refrigerant enters the evaporator, the refrigerant is cooler than the air from the blower fan. The heat in the air flows into the cooler low pressure liquid refrigerant. Some of the refrigerant boils and changes into refrigerant gas. The heat laden low pressure refrigerant gas/liquid combination flows to the accumulator. The cooler air flows back into the operator's compartment. STMG 745 5/03 - 33 - ACCUMULATOR WITH DESICCANT WITHOUT DESICCANT INLET INLET VAPOR LINE OIL BLEED HOLE DESICCANT OUTLET OUTLET 22 Accumulator • Gas/liquid mixture The accumulator stores the refrigerant gas/liquid mixture and allows only gas refrigerant to flow to the compressor. The refrigerant gas flows through the opening (inlet) at the top of the vapor line. • Earlier accumulators Earlier accumulators contain a diverter cap to keep the liquid away from the opening in the vapor line. The oil bleed hole allows oil to flow back to the compressor. • Desiccant bag Some accumulators contain a desiccant bag to remove moisture from the refrigerant. On systems with an in-line dryer, the desiccant is removed from the accumulator and placed in the in-line dryer. STMG 745 5/03 - 34 - THERMOSTATIC EXPANSION VALVE SYSTEM CONDENSER COIL COMPRESSOR RECEIVER-DRYER CONDENSER FAN CAPILLARY TUBE EXPANSION VALVE TO COMPRESSOR EVAPORATOR COIL EVAPORATOR FAN High Pressure Gas Low Pressure Gas High Pressure Gas/Liquid Mix Low Pressure Gas/Liquid Mix High Pressure Liquid 23 Thermostatic Expansion Valve System Many earlier model machines are equipped with the thermostatic expansion valve system. The purpose of the thermostatic expansion valve is to: • Restrict refrigerant - Restrict refrigerant flow and allow the compressor to increase the pressure on the high side of the air conditioning system • Control refrigerant - Control the amount of refrigerant entering the evaporator • High side The part of the air conditioning system from the compressor outlet to the expansion valve inlet is called the "high side." The thermostatic expansion valve causes a restriction to refrigerant flow that increases the pressure between the expansion valve (restriction) and the compressor. The increase in pressure allows the refrigerant to change from a gas to a liquid. STMG 745 5/03 • Increase temperature • Pressure decrease - 35 - Just as the compressor increases the temperature of the refrigerant by concentrating the refrigerant into a smaller space, the expansion valve decreases the temperature by allowing the refrigerant to spread out as it leaves the orifice in the expansion valve. Because the pressure is greatly decreased, the refrigerant is coldest as the refrigerant leaves the expansion valve and enters the evaporator. The part of the air conditioning system from the expansion valve outlet to the compressor inlet is called the "low side." The thermostatic expansion valve system is equipped with a receiverdryer. STMG 745 5/03 - 36 - EXPANSION VALVES TUBE TUBE DIAPHRAGM PIN DIAPHRAGM INLET INTERNAL EQUALIZER PASSAGE ORIFICE SEAT SUPERHEATER SPRING INLET EXTERNAL EQUALIZER TUBE ORIFICE SEAT PIN SUPERHEATER SPRING THERMAL BULB OUTLET OUTLET THERMAL BULB INTERNALLY EQUALIZED EXTERNALLY EQUALIZED 24 Thermostatic Expansion Valve • Internally equalized • Externally equalized • Thermal bulb • Diaphragm • Valve seat • Orifice Two types of expansion valves are used on machines: internally equalized and externally equalized. Both the internally equalized and the externally equalized expansion valves have a thermal bulb connected to a diaphragm by a small tube. The thermal bulb contains a refrigerant. A clamp holds the thermal bulb securely to the evaporator exhaust line. The thermal bulb is sensitive to exhaust temperature. If the exhaust temperature increases, the refrigerant inside the bulb expands. The expanding refrigerant exerts pressure against the diaphragm in the top of the valve. The diaphragm is connected through a pin to the valve seat. Pressure exerted against the diaphragm causes the diaphragm pin and valve seat to move. As the valve seat moves away from the orifice, more refrigerant flows into the evaporator. An increase in the flow of refrigerant causes the evaporator exhaust to become cooler. The cooler exhaust temperature causes the refrigerant to condense in the thermal bulb, reducing the pressure against the diaphragm, pin and valve seat. The valve seat moves to reduce flow through the orifice. STMG 745 5/03 • Gas expansion - 37 - In the internally equalized valve, the pressure of the refrigerant entering the evaporator acts on the bottom of the diaphragm through the internal equalizing passage. Gas expansion in the thermal bulb must overcome the internal balancing pressure and the spring before the valve will open to increase refrigerant flow. • Exhaust line On the external equalizer valve, the pressure acting on the bottom of the diaphragm comes from the evaporator exhaust line through an equalizer tube. The equalizer tube balances the evaporator exhaust pressure against the pressure caused by the expansion of the gas in the thermal bulb. • Superheat The superheat spring prevents surges of excessive liquid from entering the evaporator. "Superheat" is an increase in temperature of the refrigerant gas above the temperature at which the refrigerant evaporated. The superheat spring is installed against the valve and is adjusted to a predetermined setting at the time of manufacture. • Spring tension The expansion valve is designed so that the temperature of the refrigerant at the evaporator exhaust line must have 3°C (5°F) of superheat before more refrigerant is allowed to enter the evaporator. The spring tension is the determining factor in the opening and closing of the expansion valve. During opening and closing, the spring tension retards or assists valve operation as required. STMG 745 5/03 - 38 - RECEIVER-DRYER FROM CONDENSER TO EXPANSION VALVE SCREEN 25 Receiver-dryer • Dry • Store • Filter • High pressure liquid The receiver-dryer has three functions: dry, store and filter liquid refrigerant. As the high pressure liquid refrigerant flows into the receiver-dryer, the refrigerant is filtered through a desiccant that removes any moisture from the refrigerant. The refrigerant is stored until needed by the system. When the system calls for refrigerant, high pressure liquid flows through a fine mesh screen fitted on the pickup tube. (The screen prevents any debris from circulating through the air conditioning system.) High pressure liquid flows from the receiver-dryer to the thermostatic expansion valve. STMG 745 5/03 - 39 - “H” BLOCK EXPANSION VALVE SYSTEM RECEIVER-DRYER CONDENSER COIL CONDENSER FAN COMPRESSOR "H" BLOCK EXPANSION VALVE High Pressure Gas High Pressure Gas/Liquid Mix High Pressure Liquid Low Pressure Gas EVAPORATOR BLOWER FAN Low Pressure Gas/Liquid Mix 26 "H" Block Expansion Valve System In the "H" Block expansion valve system the thermostatic expansion valve is replaced with the "H" Block expansion valve. • Bottom of evaporator • Evaporator fan • Refrigerant vapor • Temperature sensor • Diaphragm expands When the "H" Block expansion valve opens, liquid refrigerant is metered into the bottom of the evaporator. The low pressure refrigerant begins to boil as it flows through the evaporator coil. The refrigerant vapor attracts the heat from the warmer air circulated by the evaporator fan. The compressor draws the refrigerant vapor out of the top of the evaporator and past the temperature sensor. The cooler vapor cools the temperature sensor. As the temperature sensor cools, the gas in the sensor condenses and decreases the pressure on the top of the temperature sensor diaphragm. The diaphragm expands upward moving the rod away from the ball and spring. The ball and spring starts to close restricting flow through the expansion valve. STMG 745 5/03 • Temperature sensor - 40 - The temperature sensor controls the operation of the air conditioning system by allowing the exact amount of liquid refrigerant to be metered past the ball and spring. STMG 745 5/03 - 41 - "H" BLOCK EXPANSION VALVE DIAPHRAGM TEMPERATURE SENSOR TO COMPRESSOR FROM EVAPORATOR ROD TO EVAPORATOR FROM CONDENSER BALL AND SPRING 27 "H" Block Expansion Valve Some air conditioning systems use the "H" Block expansion valve to control the amount of refrigerant into the evaporator. • Cut-out mode • Cut-in mode During the compressor cut-out mode, the pressure on the bottom of the temperature sensor diaphragm increases above the pressure on top of the diaphragm. The diaphragm expands upward retracting the rod and allowing the ball and spring to close the valve. During the compressor cut-in mode, the pressure on the bottom of the temperature sensor diaphragm decreases rapidly. The higher pressure on the top of the diaphragm pushes the rod and ball down to open the valve. STMG 745 5/03 - 42 - COMPRESSOR ELECTRICAL CIRCUIT R-134a CAPILLARY TUBE CAPILLARY BELLOWS ASSEMBLY PIVOTING FRAME CLUTCH BATTERY POINT OPENING TEMPERATURE ADJUSTING SCREW 28 Thermostatic Switch • Cycles compressor The thermostatic switch in the compressor electrical circuit cycles the compressor, allowing the operator to adjust the amount of coolness desired and prevent the evaporator from freezing. • Stationary contact The thermostatic switch consists of a stationary contact and a pivoting frame attached to a capillary bellows assembly. The capillary tube is filled with R-134a or a similar refrigerant. The capillary tube is inserted between the evaporator core fins. The refrigerant in the capillary tube expands or contracts, depending on the temperature of the evaporator. • Capillary tube • Expands and contracts • Pivot frame The expanding and contracting refrigerant in the capillary tube causes the bellows to expand and contract. The expanding and contracting bellows causes the pivoting frame to pivot. STMG 745 5/03 - 43 - • Evaporator clutch coil Part of the wire to the evaporator clutch coil is connected to the stationary contact, and the other part is connected to the pivoting frame. The contact and pivoting frame must come together for the switch to close and operate the compressor clutch. • Stationary contact • Pivoting frame The operator regulates evaporator cooling by varying the space between the stationary contact and pivoting frame. Moving the contact and pivoting frame farther apart (decreasing cooling) causes the bellows to expand farther before closing the switch. Moving the contact and pivoting frame closer together (increasing cooling) causes the switch to close with less bellows movement. • Regulating the range Adjustable thermostats have provisions for regulating the range between the opening and closing of the switch. The adjustment screw is located under a removable cover. If the adjustable screw is not found in this location, the thermostat is non-adjustable. • Adjustment screw • Non-adjustable • Cab temperature The non-adjustable thermostat system (sometime called a Freeze Control System) contains one temperature control knob. The knob is connected to the heater control valve, which controls the flow of coolant through the heater coil. The evaporator air flow temperature is controlled by the nonadjustable thermostat. The cab temperature is maintained by monitoring the air flow across the heater and evaporator coils. When air flow across the heater and evaporator coils reaches 2° C (36° F), the non-adjustable thermostat turns the compressor ON. When air flow temperature decreases to -1° C (30° F), the non-adjustable thermostat turns the compressor OFF. STMG 745 5/03 - 44 - PULLEY ASSEMBLY DRIVE PLATE HUB COMPRESSOR CLUTCH SHAFT BEARING COIL ASSEMBLY 29 Compressor Clutch • Pulley assembly • Drive plate • Magnetic field The clutch is driven by the engine crankshaft through a belt to the pulley assembly on the magnetic clutch. The pulley assembly turns on the bearing and is not connected to the shaft. The drive plate is splined through the hub to the shaft. The coil assembly is mounted on the frame of the compressor and does not rotate. The electrical current from the thermostat creates a magnetic field in the coil assembly. The magnetic field pulls the drive plate against the pulley assembly. The pulley assembly then turns the drive plate, hub and shaft to operate the compressor. STMG 745 5/03 - 45 - 30 Low Pressure Switch • Protect the system • Magnetic clutch Shown is the low pressure-sensing switch (arrow) threaded into the receiver-dryer on one of the older systems. The pressure sensing switch is used to protect the system from damage due to the lack of refrigerant or oil. Located in the electrical circuit to the magnetic clutch, the switch opens when system pressure decreases below 175 kPa (25 psi) and shuts off the compressor. The switch can be located on the dryer, expansion valve, liquid line, or on the compressor depending on the age of the system on the machine . NOTE: Some older machines and systems have low pressure sensing systems threaded into the receiver-dryer. In case of a refrigerant leak or the system becoming undercharged, this keeps the compressor from burning up as it attempts to keep cycling, trying to cool with not enough refrigerant in the system. STMG 745 5/03 - 46 - 31 High Pressure Relief Valve • High pressure relief valve The high pressure relief valve (arrow) is located on either the compressor or the receiver-dryer. The high pressure relief valve allows the refrigerant to be released to the atmosphere if system pressure increases above 3450 kPa (500 psi). On todays systems, the high pressure relief valve opens a high pressure switch. This prevents refrigerant from being vented into the atmosphere. It is spring loaded and is able to be reset. STMG 745 5/03 - 47 - ORIFICE TUBE SYSTEM CONDENSER COIL HIGH / HIGH LOW PRESSURE SWITCH COMPRESSOR LOW PRESSURE SWITCH INLINE DRYER ACCUMULATOR EVAPORATOR COIL LOW PRESSURE SWITCH High Pressure Gas Low Pressure Gas High Pressure Gas/Liquid Mix Low Pressure Gas/Liquid Mix High Pressure Liquid Low Pressure Liquid 32 Pressure Switch Locations for Orifice Tube System • Low pressure switches • High pressure switches The Orifice Tube system above shows the locations for the High Pressure, Low Pressure, or High-Low pressure switches. The locations for switches above vary depending on what machine you are working with and are only intended to show generally where they are usually found. These low pressure switches prevent the compressor from cycling too often if the refrigerant charge is too low. The high pressure switches help protect the compressor in the event the system is overcharged with too much refrigerant. STMG 745 5/03 - 48 - “H” BLOCK EXPANSION VALVE SYSTEM CONDENSER COIL LOW PRESSURE SWITCH HIGH / HIGH LOW PRESSURE SWITCH COMPRESSOR RECEIVER-DRYER LOW PRESSURE SWITCH "H" BLOCK EXPANSION VALVE HIGH / HIGH LOW PRESSURE SWITCH LOW PRESSURE SWITCH High Pressure Gas High Pressure Gas/Liquid Mix High Pressure Liquid Low Pressure Gas Low Pressure Gas/Liquid Mix 33 Pressure Switch Locations for "H" Block Expansion Valve System • High, low, or high-low pressure switches The "H" block expansion valve system above shows the locations for the different pressure switches. Depending on machine type the High, Low, or High-Low pressure switches can be located in different locations. These switches help assure the compressor will not be damaged if something within the system changes. STMG 745 5/03 - 49 - 34 Moisture Indicator • Relative moisture • Color chart • Moisture indicator • Sight glass Shown is the moisture indicator. The moisture indicator is located in the line between the receiver-dryer and the expansion valve. The moisture indicator measures the relative moisture in the system. A moisture reference color chart is on the face of the indicator. The color blue represents a dry system and the color pink represents a wet system. The moisture indicator should be checked at the end of each shift. To check the moisture indicator, look at the indicator ring (2) through the sight glass (1). If indicator ring is blue in color, the system is dry. If indicator ring is pink in color, the system has moisture. The moisture must be removed and the receiver-dryer must be changed. NOTE: Instructions for removing moisture from the system and changing the receiver-drier are covered in the Service Manual "Air Conditioning and Heating" (Form SENR5664-08). NOTE: Moisture indicators have generally been removed from most of the systems in 1999 because of the inaccuracy of the color change and misinterpretation of the color meaning by field personnel. STMG 745 5/03 - 50- KEEP UPRIGHT DO NOT HEAT KEEP AWAY FROM FLAME WEAR SAFETY GLASSES DO NOT FREEZE DO NOT DROP R-134a DANGER WEAR GLOVES WHEN HANDLING 35 WARNINGS The following warnings should be observed when servicing air conditioning systems, operating air conditioning equipment or handling refrigerants. • Protective goggles 1. Wear protective goggles. Escaping refrigerant coming in contact with the eyes can cause serious injury. • Excessive heat 2. Do not use excessive heat on refrigerant containers during the charging process. Never use direct heat. Use a container of water that does not exceed 52°C (125°F). • Ozone layer 3. Do not discharge refrigerant to the atmosphere. In addition to being harmful to the earth's ozone layer, Refrigerant 12 when subjected to an open flame results in a very deadly phosgene gas. Refrigerant 134a gives off harmful vapors also when exposed to flame. STMG 745 5/03 - 51- • Ventilated area 4. Always work in a well ventilated area. Inhaling refrigerant, even in small amounts, can be cumulative and cause light-headedness. Refrigerants can also cause irritation to the eyes, nose and throat. • Excessive pressure 5. Do not weld or steam clean near vehicle installed air conditioning lines. The heat can cause excessive refrigerant pressure. • Leak testing 6. Do not mix R-134a with air for the purpose of leak testing. When under pressure the mixture could explode. • Engine running 7. When charging a system with the engine running, be sure the high pressure gauge valve is closed. • Rotating components 8 Be alert when the engine is running and stay clear of rotating components. • Disposable tank 9. Do not recover or transfer refrigerant into a disposable tank. Always use a DOT approved tank. Look for DOT4BA or DOT4BW on the tank. • Storage tank 10. Do not fill a storage tank to more than 60% of its gross weight rating. • Transport 11. Do not transport refrigerant in passenger compartment of a vehicle. • Exposure 12. Do not expose refrigerant to open flames, high temperatures or direct sunlight. STMG 745 5/03 - 52- 36 AIR CONDITIONING PERFORMANCE TESTS Visual Inspection, Engine Off • System performance Correct air conditioning system performance is the number one objective whether conducting preventive maintenance or a major repair. When doing a performance test, the first step is a visual inspection of the air conditioning system components. The visual inspection is performed with the engine OFF. STMG 745 5/03 - 53- 1 2 37 • Drive belt The compressor drive belt may be damaged or loose. A damaged drive belt must be replaced. During inspection, check for cracks (1) or damage in the belt’s surfaces. Check for delamination (2) which is a separation which can occur between the belt’s back and main core. If any of the above characteristics are found, replace the belt. • Belt tension gauge When installing a new belt or tightening a loose belt, use the Caterpillar belt tension gauge. See the Service Manual for belt tightening specifications. • Restricted air flow Inspect the condenser for trash, dirt and other debris that can restrict air flow. Insufficient air flow through the condenser can cause poor cooling and lead to compressor damage. STMG 745 5/03 - 54 - 38 • Air passages • Dirt and debris • Fresh air The evaporator blower or fan can only be effective when air passages are clear. Condensation traps dirt and debris on the blower side of the evaporator. The dirt and debris form a coating that restricts evaporator air flow. The coating must be removed. Inspect the fresh air and recirculating air filters. Clean or replace the filters as needed. STMG 745 5/03 - 55 - 39 • Blower motor • Noisy motor Check the blower motor for satisfactory operation. Operate the blower motor at all speeds. (Turn the key switch ON if needed to provide power to the blower motor.) Make repairs if the air flow does not increase as the control is moved from low speed to higher speeds, if the motor is noisy and/or if the motor fails to operate in some speeds. STMG 745 5/03 - 56 - 40 • Air ducts Operate all air ducts and louver controls. The controls should move freely without sticking or binding. STMG 745 5/03 - 57 - 41 Operation Inspection, Engine On • Operating temperature When making the air conditioning operation checks, the engine should be at normal operating temperature and the air conditioning system must be stable. • Gauge set - Install the manifold gauge set. • 1000 rpm • Maximum speed • Increase engine speed • Operational checks - Start the engine and increase the engine speed to approximately 1000 rpm. - Turn on the air conditioning system. Move the temperature control to the MAXIMUM position. Move the fan switch to the HIGH position. Operate for 10 - 15 minutes making sure the doors and windows are closed. - Increase the engine speed to 1300 - 1400 rpm. - Conduct the air conditioning system operational checks. STMG 745 5/03 - 58 - 1 2 3 4 8 5 7 6 42 • Checking performance • Hoses The manifold gauge set is an important tool in checking performance, diagnosis and servicing of the air conditioning system. The gauge set is composed of a low side (compound) gauge (1), a manifold (2) to which the gauges are connected and a high side gauge (3). The high side hand valve (4) and low side hand valve (8) allow the system to be evacuated and serviced through the manifold. The low side hose connector (7) and high side hose connector (5) connect the gauge manifold to the air conditioning system. The center service hose (6) connects the manifold gauge to an external source. Manifold gauge pressures will be affected by the ambient temperature. High side pressures are affected more than the low side pressures. • Ambient temperature • Low side pressure • High side pressure • Service manual When the ambient temperature is above 21°C (70°F), the low side pressure should read from 70 to 210 kPa (10 to 30 psi) depending on the ambient temperature and the machine being tested. The high side pressure should read from 820 to 2075 kPa (120 to 300 psi) depending on the ambient temperature and the machine being tested. See Table 12 in the Service Manual (SENR5664) for Pressure Range Reference. No two systems will have the exact same manifold gauge readings. Allow for variations in pressures. NOTE: Gauge pressures should be used only as a guide when working with 134a and must be used in conjunction with system pressures. STMG 745 5/03 - 59 - 1 2 43 • Schrader valves Schrader Valves Schrader valves are used to attach the manifold gauge set to the air conditioning system. The Schrader valves effectively seal the refrigerant inside the system until service work is needed. • High side smaller The Schrader fitting on the high side (1) is smaller than the fitting on the low side (2). The difference in fitting sizes is to prevent connecting the manifold gauge set to the wrong pressure side. STMG 745 5/03 - 60 - SCHRADER VALVE AND SERVICE HOSE SCHRADER VALVE PIN VALVE CORE DEPRESSOR SERVICE GAUGE PORT COMPRESSOR FITTING 44 Service Hose • Schrader core depressor Shown is a sectional view of a Schrader valve and a service hose with a Schrader core depressor. As the high and/or low side pressure hose is threaded onto the Schrader valve service port, the Schrader core depressor in the hose depresses the pin in the center of the Schrader valve. The valve is opened allowing refrigerant to flow between the manifold gauge set and the compressor. When the hose is removed, the valve closes automatically. STMG 745 5/03 - 61 - PERFORMANCE TEST LOW SIDE (COMPOUND) PRESSURE GAUGE 40 HIGH SIDE PRESSURE GAUGE 2 80 3 20 450 600 750 900 300 10 1 120 20 10 1050 4 150 30 1200 0 0 160 25 50 20 30 a kP SI P 10 100 k PS Pa I 0 40 5 6 CENTER INTERNAL PASSAGE LOW SIDE HAND VALVE HIGH SIDE HAND VALVE HIGH SIDE INTERNAL PASSAGE LOW SIDE INTERNAL PASSAGE HIGH SIDE SERVICE CONNECTOR LOW SIDE SERVICE CONNECTOR CENTER SERVICE CONNECTOR 45 Performance Test • Performance test • Compound gauge • Low side Shown is a sectional view of the manifold gauge set used in a performance test. The hand valves are open on both the low and high sides. The compound gauge is connected to the low pressure side. The low side service connector is connected through a hose (not shown) to the low pressure side of the air conditioning system. When the low side hand valve is closed, the compound gauge shows only the low side pressure reading. • High side The high pressure gauge is connected to the high pressure side. The high side service connector is connected through a hose (not shown) to the high pressure side of the air conditioning system. When the high side hand valve is closed, the high pressure gauge shows only the high side pressure reading. • Center passage The center internal passages in the manifold connect the center service connector to the low and high side passages. During a performance test, the closed hand valves isolate the low and high side passages from the center service connector. STMG 745 5/03 - 62 - ADDING REFRIGERANT LOW SIDE (COMPOUND) PRESSURE GAUGE 40 2 80 3 20 600 450 10 750 900 300 1 120 20 10 1050 4 150 30 1200 0 0 160 25 50 20 100 30 a kP SI P 10 k PS Pa I 0 40 5 6 CENTER INTERNAL PASSAGE LOW SIDE HAND VALVE LOW SIDE INTERNAL PASSAGE CENTER SERVICE CONNECTOR 46 Adding Refrigerant • Adding refrigerant • Refrigerant flow Shown is a sectional view of the manifold gauge set when adding refrigerant to the system. Opening the low side hand valve opens the center service connector to the low side service connector and the low side gauge. Refrigerant flows into the center service connector, through the manifold gauge and out through the low side service connector. The compound gauge registers the low side pressure during the operation. STMG 745 5/03 - 63 - 47 High Side - Low Side Temperatures • Temperature check • High side • Low side With the air conditioner running, carefully check the relative temperatures at the HIGH and LOW SIDE of the system. HIGH SIDE temperature should vary from "hot" at the compressor discharge to "warm" at the expansion valve. Any sudden drop in temperature indicates a partial blockage at that point. LOW SIDE temperature should be "cool." There may be large sweating or frosting of the suction line from the evaporator to the accumulator depending on the ambient temperature. NOTE: Frosting can occur to the compressor on the return line for 134a systems. Note the gauge pressures on the 134a system are not accurate enough for charging the system. R134a systems must be charged by weight or temperature only! Refer to SENR5664-08 for charge weights. Use a scale and tank for charging. Do not use small cans. Do not add to or remove refrigerant from a weighed charge and do not use gauges to determine the charge. If in question, remove complete charge and recharge by weight. STMG 745 5/03 - 64 - 48 Ambient Temperature vs. Barometric Pressure • Temperature control • Thermometer • Temperature difference With the engine speed set at 1300 to 1400 rpm, set the temperature control to the MAXIMUM cool position and the fan switch in the HIGH position. Run the air conditioning system for 15 to 20 minutes with doors and windows closed. Place a thermometer in the blower air outlet duct and record the reading. Then use the thermometer to read the ambient (outside) air temperature. The temperature difference between the air from the air duct and the ambient air should be as follows: Ambient Air Temperature Difference (minimum) Below 24°C (75°F) 11°C (20°F) Between 24 - 32°C (75 - 90°F) 14°C (25°F) Above 32°C (90°F) 17°C (30°F) NOTE: The readings above are general ranges and can fluctuate slightly due to changes in barometric pressure, humidity and the condition of the charge in the system STMG 745 5/03 - 65 - 1 2 49 Refrigerant Tanks • Standard tank • DOT approval • Tank fill • Expansion The standard tank (1) in which refrigerant is sold should never be used to reclaim refrigerant. Refrigerant tanks (2) used on recovery/recycling equipment must be approved by the Department Of Transportation (DOT). DOT approval is indicated by "DOT 4BW" or "DOT 4BA" stamped into the tank. NOTE: The closed tanks should not be filled with liquid over 80% of the tank volume. The remaining 20% (called "head pressure room") is left for liquid expansion. STMG 745 5/03 - 66 - 50 Air Conditioning Service Tools • Special tools When servicing an air conditioning system, many special tools are needed in addition to the basic mechanic's tool box. Several special tools are covered in the following materials. STMG 745 5/03 - 67 - 51 Electronic Leak Detector • Finding leaks • Detector beeps • Very small leaks The electronic leak detector is considered the most accurate means of finding a leak in the system. Many electronic detectors can detect small leaks equivalent to 1/2 oz. per year. The detector will "beep," activate a light or both when a leak is found. To obtain accurate results, leak detection must be performed with the system under pressure. A 50% refrigerant charge in the system is enough to locate most leaks. However, very small leaks may require the system pressure to be increased above normal before the leaks can be located. STMG 745 5/03 - 68 - 52 Recover, Evacuate and Charge Unit • Recovery unit The refrigerant recovery unit should be used to recover refrigerant from the air conditioning system when making repairs. The refrigerant can then be recycled and reused in the system after the repairs are completed. • One step recovery An automatic air conditioning recover, evacuate and charge unit may be used to perform a one step recovery, evacuating and charging operation. The evacuation time and the amount of refrigerant charge are both programmed into the unit. After the refrigerant has been recovered, the unit will evacuate and charge the air conditioning system automatically. A large variety of units are available. Some units (such as the unit shown) are used to recover, recycle, evacuate and charge refrigerant. Other units may only recover the refrigerant. The refrigerant is then transferred to a recycling unit to be recycled. STMG 745 5/03 - 69 - 53 Vacuum Pump • Remove air and moisture The vacuum pump completely removes all air and moisture from the air conditioning system by lowering the pressure within the system to a point where moisture turns to a vapor. The vapor is them pumped out of the system with the air. To remove all moisture from the system, the vacuum pump should operate with the low pressure gauge at 981 mbar (29 in. Hg) for a minimum of 30 minutes. NOTE: All refrigerant should be recovered from the system before connecting the vacuum pump. STMG 745 5/03 - 70 - 1 2 54 Refrigerant Charging Scales • Refrigerant Charging Scales 1. Manual operated 2. Automatic The two types of refrigerant charging scales are the manual operated type (1) and the automatic type (2). Each type allows the specified amount of refrigerant to be added to the system regardless of the ambient temperature. The charging scale is the recommended method when charging the air conditioning system on Caterpillar machines. STMG 745 5/03 - 71 - 55 Refrigerant Analyzer • Vital tool The refrigerant analyzer is a vital tool in air conditioning service. • Identifies refrigerant The refrigerant analyzer identifies the refrigerant, measures the percentage of purity, indicates the percent of air in the system and indicates blends and contaminated refrigerants. • Recovery equipment contamination Using the refrigerant analyzer will prevent possible contamination of the recovery equipment with refrigerants other than the one specified for use. STMG 745 5/03 - 72 - 56 Air Conditioning Component Flusher • Flushing solution The A/C component flusher uses shop air to atomize the flushing solution. The solution is used to remove residue and other contaminants from the hoses, evaporator and condenser. STMG 745 5/03 - 73 - 57 CONCLUSION This presentation has discussed the basic air conditioning principles, the basic vehicle air conditioning system components and the component functions as they relate to the operation of the air conditioning system. Warnings and the correct procedures for inspecting and servicing the air conditioning system have also been covered. Always check the appropriate Service Manual for the latest service information and specifications when servicing, testing and adjusting, and/or making repairs. STMG 745 5/03 - 74 - SLIDE LIST 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. Orifice tube system schematic Pot of boiling water Fireplace and block of ice Thermometer in pot of boiling water Drops of dye in water Adding sensible heat to water Latent heat melting ice Ice, liquid and vapor Atmospheric pressure Three pots of boiling water Gas being compressed in a piston Flask, compound gauge and vacuum pump R134a warnings Flask of R134a Flask, compressor and flask Flask, compressor, flask and orifice Orifice tube system schematic Cut-a-way of compressor Flow through condenser In-line dryer and orifice tube Flow through evaporator Cut-a-way of accumulator Thermostatic expansion valve system Cut-a-way of expansion valve Cut-a-way of receiver dryer "H" block expansion valve system Cut-a-way of "H" block expansion valve Compressor electrical circuit schematic Cut-a-way of compressor clutch Low pressure switch High pressure switch Orifice tube system H block expansion valve Moisture indicator Warnings 4-in-1 slide Visual inspection 4-in-1 slide Compressor belt 4-in-1 slide Evaporator/blower/fan 4-in-1 slide Blower motor switch 4-in-1 slide Air ducts and louvers 4-in-1 slide 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. Operation inspection 4-in-1 slide Manifold gauge set Schrader service valves Cut-a-way of schrader valve Cut-a-way of manifold gauge (performance test) Cut-a-way of manifold gauge (adding refrigerant) Temperature check 4-in-1 slide Evaporator output 4-in-1 slides Refrigerant tanks Service tools 4-in-1 slide Electronic leak detector Recovery, evacuate and charge unit Vacuum pump Refrigerant charging scale Refrigerant analyzer A/C flushing unit A/C tools 4-in-1 slide STMG745 5/03 BASIC AIR CONDITIONING SYSTEM CONDENSER COIL COMPRESSOR RECEIVER-DRYER - 75 - CONDENSER FAN CAPILLARY TUBE EXPANSION VALVE TO COMPRESSOR EVAPORATOR FAN Serviceman's Handout No. 1 EVAPORATOR COIL STMG 745 5/03 CONDENSER COIL COMPRESSOR CONDENSER FAN ACCUMULATOR ORIFICE TUBE SYSTEM EVAPORATOR BLOWER FAN Serviceman's Handout No. 2 EVAPORATOR COIL - 76 - INLINE DRYER STMG 745 5/03 CONDENSER COIL RECEIVER-DRYER EVAPORATOR BLOWER FAN COMPRESSOR "H" BLOCK EXPANSION VALVE SYSTEM Serviceman's Handout No. 3 "H" BLOCK EXPANSION VALVE - 77 - CONDENSER FAN - 78 - Serviceman's Handout No. 4 4. 1. 3. 5. 2. STMG 745 5/03 - 79 - Serviceman's Handout No. 5 4. 2. 1. 5. 3. STMG 745 5/03 - 80 - Serviceman's Handout No. 6 4. 1. 5. 3. 2. STMG 745 5/03 Serviceman's Handout No. 7 0°C (32°F) - 81 - 100°C (212°F) STMG 745 5/03 STMG 745 5/03 - 82 - INSTRUCTOR NOTES STMG 745 5/03 - 83 - INSTRUCTOR NOTES STMG 745 5/03 - 84 - INSTRUCTOR NOTES SERV1745 5/03 Printed in U.S.A.