start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 49, the reader should be able to: • Prepare for ASE Heating and Air-conditioning (A7) certification test content area “A” (Air conditioning System Diagnosis and Repair) and content area “C” (Heating and Engine Cooling Systems Diagnosis and Repair) • • Describe how the heater functions Describe how the refrigeration cycle functions Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 49, the reader should be able to: • • List the parts of a typical air-conditioning system Explain how the air-conditioning system removes heat from the passenger compartment Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: absolute humidity • axial compressor barrier hose • blower motor • boiling point calorie (c) • capillary tube • CFC-12 (R-12) • compressor • condensate line • condensation point • cycling clutch orifice tube (CCOT) ester oil • electromagnetic clutch • evaporator • evaporator pressure regulator (EPR) valve freon Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: heat • heater core • heater hoses • heating, ventilation, and airconditioning system (HVAC) • HFC-134a (R-134a) • humidity • H-valve • hygrometer kinetic energy • latent heat of vaporization • liquid • miscible pilot operated absolute (POA) valve • pintle valve • positivedisplacement compressor • psychrometer reed valve • relative humidity Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: section 609 (clean air act) • solid • superheat • swash plate thermostatic expansion valve (TEV or TXV) system • thermo switch (icing switch or defrost switch) vapor Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PRINCIPLES OF HEATING AND REFRIGERATION Driver and passenger comfort is the primary purpose of the heating, ventilation, and airconditioning system, abbreviated HVAC Matter is found in three different states: solid, liquid, or vapor (gas) The state depends upon the nature of the substance, the temperature, and the pressure or force exerted on it Figure 48–1 Water is a substance found naturally in solid, liquid, and vapor states Water occurs naturally in all three states: solid ice, liquid water, and water vapor, depending upon temperature and pressure of the location Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Changes of State A solid cannot be compressed and has strong resistance to flow Molecules of a solid attract each other strongly, and resist changes in volume and shape A substance is solid at any temperature below its melting point The melting point is a characteristic of a substance, and the temperature at which a solid turns liquid For water, melting point is 32°F (0°C), A liquid is a substance that cannot be compressed A substance in a liquid state has a fixed volume, but no definite shape The boiling point is the temperature at which a solid substance turns to a vapor For water at normal seal level conditions, the boiling point is 212°F (100°C) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Vapor can be easily compressed, has no resistance to flow, and no fixed volume It is considered a fluid just like liquids are A substance changes to a vapor if the temperature rises above its boiling point A vapor condenses to liquid if the temperature falls below it Like melting and freezing, boiling point and condensation point are the same temperature, and vary with pressure Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Heat and Temperature Molecules vibrate rapidly in all directions; disorganized energy is called heat Intensity of vibration depends kinetic energy, or energy of motion, the atom or molecule contains We measure the level of this energy as temperature Heat and temperature are not the same Heat is measured in calories (c) The calorie is a metric unit for the amount of heat needed to raise the temperature of one gram of water one degree Celsius Heat is also measured in British Thermal Units (BTU) One BTU is the heat required to raise the temperature of one pound of water 1°F at sea level One BTU equals 252 calories Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Positive-Displacement Piston Compressors Most automotive air-conditioner compressors are positive-displacement compressor designs They displace a uniform volume of refrigerant for each revolution or operating cycle, and have from one to 10 cylinders Figure 48–34 In a positive-displacement compressor, the descending piston creates a drop in pressure inside the cylinder The resulting pressure differential allows low-side pressure to force the suction valve open Refrigerant then flows into the cylinder On the piston’s discharge stroke, the pressure caused by the ascending piston closes the intake valve and forces the refrigerant out the discharge valve Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The compressor intake stroke is also known as the suction stroke As the compressor operates, the maximum possible charge of refrigerant vapor has been drawn in at bottom dead center of the compressor piston’s suction stroke When the piston begins its discharge stroke, the pressure increases, shutting the suction valve and opening the discharge valve at the same time The charge of refrigerant vapor is pushed out of the compressor into the high-side refrigerant line and travels toward the condenser The refrigerant vapor is compressed simultaneously throughout the entire high side of the air-conditioning system Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 All piston compressors use one suction valve and one discharge valve for each piston The typical valve used in compressors is the reed valve: a one-way, flap-type check valve that is built into the valve plate which seals one or more cylinders Figure 48–35 A reed valve is a one-way check valve that flaps away from the valve plate to open, and toward the valve plate to close Pressure pushes the valve in one direction or the other The suction reed valve is located on the underside of the valve plate The refrigerant vapor fills the partial vacuum created by the moving piston Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The discharge reed valve is on the top side of the valve plate The partial vacuum in the cylinder also pulls the discharge valve tightly against its seat, sealing off the system’s high side from the cylinder during the suction stroke The reeds behave the opposite way during the piston’s discharge stroke The increasing cylinder pressure pushes the suction valve tightly against its seat, sealing off the system’s low side The discharge valve on the opposite side of the valve plate is unseated as the pressure in the cylinder increases as a result of the upward moving piston The piston pushes the refrigerant through the discharge valve, out of the compressor, and into the air-conditioning system high side Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Pistons and Rings The two-stroke cycle depends upon the pistons and sealing rings to provide an adequate seal against high-side refrigerant pressure Some compressors use a swash plate, or axial plate, rigidly mounted to the belt-driven shaft at an angle As the pulley turns, the shaft and angled swash plate assembly rotate This forces the pistons back and forth in their bores Compressors that use a swash plate are often called axial compressors Figure 48–36 The swash plate, attached to the crankshaft at an angle, converts the pulley’s rotary motion to axial motion, which drives the pistons in a reciprocating motion Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Variable Displacement Compressor Some systems use variable displacement to control amount of refrigerant flow through the evaporator The pressure difference between high side and low side causes the swash plate to move inside the compressor As the swash plate changes its angle, the stroke of the piston is increased for more cooling or decreased to reduce the amount of cooling Figure 48–37 A V-5 variable displacement compressor Internal pressures act on the swash plate, which changes the stroke of the piston and then displacement based on the pressures in the system Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The Radio “POP” Trick Most air-conditioning compressor clutch circuits contain a diode used to suppress high-voltage spikes generated whenever the compressor clutch coil is disengaged (turned off) If this diode were to fail, a high voltage (up to 400 volts!) could damage sensitive electronic components in the vehicle including the electronic air-conditioning compressor clutch control unit (if so equipped) The radio will often turn off, then back on, whenever the electronics inside the radio detect a high-voltage spike This can create a “pop” in the radio that is very intermittent because it only occurs when the airconditioning compressor clutch cycles off To check this diode, simply tune the radio to a weak AM station near 1400 Hz and cycle the air-conditioning compressor on and off If a “pop” is heard from the radio, the diode is defective and needs replaced NOTE: While some compressor diodes can be replaced separately, some air-conditioning clutch diodes are part of a wiring harness assembly Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 COMPRESSOR CONTROLS Most air-conditioning compressors use an electromagnetic clutch A coil of wire inside the clutch creates a magnetic field that connects the input shaft of the compressor to the drive pulley About to amperes of current are required to energize the airconditioning compressor clutch Most vehicle manufacturers connect several components in series with the compressor clutch so that all have to be functioning before the compressor clutch can be engaged Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The most commonly used switches include: Low-pressure switch This switch is electrically closed only if there is at least 25 PSI of refrigerant pressure This amount of pressure means the system is sufficiently charged to provide lubrication for the compressor This switch also prevents the compressor from being engaged when the temperature is low (low temperature means low refrigerant pressures) Figure 48–38 Typical air-conditioning pressure switches A service manual would be needed to determine the function of each switch One switch could be the low-pressure switch and the other a high-pressure switch Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 High-pressure switch This pressure switch is located in the highpressure side of the air-conditioning system If the pressure exceeds a certain level (typically 375 PSI [2,600 kPa]), the pressure switch opens, thereby preventing possible damage to the air-conditioning system due to excessively high pressure Power steering pressure switch This switch is used on many vehicles, especially those with four-cylinder engines It opens the circuit to the air-conditioning compressor clutch when the driver turns the steering wheel This reduces the load on the engine at the same time power is needed by the power steering pump Because the wheel is seldom held in a turning maneuver for a long period of time, this stoppage of the air-conditioning compressor has little, if any, effect on passenger cooling Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 What Throttle Switch? A service technician was tracing the cause of an inoperative air compressor on a Saab The service manual showed a schematic of the air-conditioning compressor that indicated a number of switches that had to be closed for the compressor clutch to be supplied with battery voltage Besides the low pressure switch (to assure that the system is charged so as not to damage the compressor), a throttle switch was shown on the schematic Obviously, someone else had worked on the vehicle because the throttle switch was missing entirely—just two wires remained to indicate that anything had been installed Connecting the two wires together provided voltage to the air-conditioning compressor clutch The customer decided not to replace the throttle switch after learning that its purpose was to disconnect (open circuit) the air-conditioning compressor when the throttle was at wide open positive to allow the maximum power for passing Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY Engine coolant flows through heater hoses and through a heater core to provide heat to the inside of the vehicle The refrigeration cycle uses a compressor to circulate a refrigerant through a closed system Refrigerant expands in the evaporator When the refrigerant expands, both its pressure and its temperature drop Air from inside the vehicle is cooled as it passes through the evaporator The compressor forces the refrigerant through the closed system and raises the temperature of the refrigerant so that the refrigerant will condense back into a liquid in the condenser Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Airflow through the condenser removes heat from the hot refrigerant, which condenses back into a liquid The expansion valve (or orifice tube) causes the refrigerant to expand When the refrigerant expands, its pressure and temperature both drop, thereby cooling the evaporator Temperature (thermostatic) or pressure controls (EPR, POA, or VIR) prevent the freezing of the evaporator by keeping the temperature of the evaporator above freezing (32°F or 0°C) CFC-12 is commonly called Freon and is a chlorofluorocarbon (CFC) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) HFC-134a is less harmful to the environment because it does not contain any CFCs 10 A desiccant is used either in the receiver-drier or accumulator to remove any moisture that may get into the system Moisture and refrigerant combine to form harmful acid 11 The airflow through the evaporator and heater core help condition the air by removing humidity and directing the airflow where needed Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458