chap50 pps Automotive technology at University of Cambridge

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 50, the reader should be able to: • Prepare for ASE Heating and Air Conditioning (A7) certification test content areas: —“A”(Air Conditioning System Diagnosis and Repair), content area —“B” (Refrigeration System Component Diagnosis and Repair), content area —“C” (Heating and Engine Cooling Systems Diagnosis and Repair, content area 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 50, the reader should be able to: • • Prepare for ASE Heating and Air Conditioning (A7) certification test content areas: —“D” (Operating Systems and Related Controls Diagnosis and Repair), and content area —“E” (Refrigeration, Recovery, Recycling, and Handling) Diagnose lack of heat problems 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 50, the reader should be able to: • • • • List the air-conditioning system performance check procedures Discuss methods used to locate the source of an air-conditioning system leak Describe how to recover, evacuate, and recharge an air-conditioning system Discuss what is necessary to retrofit a CFC12 system to to use HFC-134a refrigerant 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: bleeder valves high-side pressure low coolant level low-side pressure 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 HVAC DIAGNOSTIC PROCEDURE When diagnosing a heating and air-conditioning system problem, most vehicle manufacturers recommend the following steps: Step #1 Verify the customer complaint (concern) Sometimes the customer does not understand how the system is supposed to work or does not explain the fault clearly Verifying means that the tech can verify that the problem has been corrected after service Step #2 Do a thorough visual inspection HVAC problems are often found by looking carefully at all of the components, checking for obvious faults or damage due to an accident or road debris Step #3 Check for diagnostic trouble codes Many systems use sensors and actuators, which are computer controlled 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 Step #4 Check for related technical service bulletins (TSBs) If there has been a bulletin released to solve a known problem, it saves time knowing what to rather than trying to find and correct Step #5 Determine the root cause Find and correct the root cause of the problem Low refrigerant level means there was a leak in the system Finding and correcting the leak correcting the root cause Step #6 Verify the repair Drive the vehicle under similar conditions which caused the customer to complain and verify that the concern has been corrected 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 HEATER DIAGNOSIS Most heat absorbed from the engine by the cooling system is wasted Some of this heat is recovered by the vehicle heater Air is passed across the heater fins and sent to the passenger compartment In some vehicles, the heater and air conditioning work in series to maintain vehicle compartment temperature Figure 50–1 The heater core is mounted inside a heater plenum chamber where air passes over it to absorb heat from the warmed engine coolant 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 HEATER PROBLEM DIAGNOSIS When the vehicle’s heater does not produce the desired amount of heat, many owners and technicians replace the thermostat before doing any other troubleshooting Many other causes besides a defective thermostat can result in lack of heat from the heater To determine the exact cause, follow this procedure: Step #1 If the engine is up to proper operating temperature, the upper radiator hose should be too hot for you to keep your hand on it The hose should also be pressurized a If the hose is not hot enough, replace thermostat b If the hose is not pressurized, test it Replace the pressure cap if it will not hold specified pressure c If okay, see step 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 Step #2 With the engine running, feel both heater hoses (Heater should be set to the maximum heat position.) Both hoses should be too hot to hold If both hoses are warm (not hot) or cool, check the heater control valve for proper operation If one hose is hot and the other (return) is just warm or cool, remove both hoses from the heater core or engine and flush the heater core with a garden hose HINT: Heat from the heater that “comes and goes” is most likely the result of low coolant level Usually with the engine at idle, there is enough coolant flow through the heater at higher engine speeds, however, the circulation of coolant through the heads and block prevents sufficient flow through the heater 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 Figure 50–11 Lack of proper airflow across the condenser is usually the cause of this condition 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’s Wrong When the A/C Compressor Clutch Cycles On and Off Rapidly? This is common on a vehicle equipped with a cycling clutch orifice tube (CCOT) system that is low on refrigerant charge With a normal charge, the low-side pressure should be 15 to 35 PSI and the clutch should be on for 45 to 90 seconds and be off for only about 15 to 30 seconds High Side Pressure Tip A quick and easy way to determine the correct high-side pressure is to add 100 to the ambient air temperature in Fahrenheit For example: 85ºF outside air temperature + 100 185 PSI typical normal high-side pressure 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 Clogged Orifice Tube Test A clogged orifice tube is a common air-conditioning system failure A clogged tube blocks refrigerant flow through the evaporator, which causes reduced cooling of the passenger compartment To check for a possible restriction in the system, follow these easy steps: Step # Connect the A/C pressure gauge to both low- and high-side pressure fittings Step # Operate the A/C system for to 10 minutes Step # Shut off the A/C system and watch the pressure gauges If pressures not equalize quickly, there is a restriction in the system NOTE: To locate a restriction in the system, feel along the system lines The restriction exists at the point of greatest temperature difference 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 Clogged Orifice Tube Test - Part Figure 50–12 A clogged orifice tube Figure 50–13 Assortment of orifice tubes Note that each is color coded and identified on the lid of the assortment Even though some technicians have purposely installed an orifice tube with a larger opening in an attempt to increase cooling, it is always safe to use the exact orifice tube specified for the vehicle being serviced 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 Fire Extinguisher Test To test the expansion valve, start the engine and allow the A/C system to function with the control set to “recirculate.” Using a CO2 fire extinguisher, blast the expansion valve with CO2 The valve should close and the low side pressure should go into a vacuum If the low-side pressure does not go into a vacuum, the expansion valve is faulty and should be replaced (a) (b) Figure 50–14 (a) A CO2 fire extinguisher equipped with the fittings necessary to test the operation of an expansion valve (b) The size of the opening at the end of the hose determines how much CO2 is released to cool the expansion valve temperature sensor bulb 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 Clogged Evaporator Problem The owner of an older Buick complained that the blower motor must be defective because the air no longer flowed from the air-conditioning vents as it should A check of the blower motor circuit revealed that the blower motor was working To confirm the operation of the blower, the resistor pack was removed and air flowed out of the opening Then the tech discovered the cause of the lack of airflow—the evaporator was covered with oily dirt The tech recovered the refrigerant and removed the evaporator Apparently, the evaporator had a small refrigerant leak that allowed the refrigerant oil to coat the fins of the evaporator Any dirt in the air stuck to the evaporator until the dirt almost completely blocked the airflow Replacing the evaporator and recharging the system fixed problem Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Figure 50–15 A partially clogged evaporator ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The Touch, Feel Test To check the state of charge of an orifice tube system, use one hand and touch the evaporator side of the orifice tube Touch the other hand to the inlet to the accumulator The following conditions can be determined by the temperature of these two locations: Normal operation Both temperatures about the same Undercharged condition Accumulator temperature higher (warmer) than the orifice tube temperature High pressure means that the temperature of the component or line will also be high (hot) Low pressure means that the temperature of the component or line will also be low (cold) 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 Figure 50–16 If the system is fully charged, the outlet temperature of the line leaving the evaporator should be about the same as the temperature of the line entering the evaporator after the expansion valve The low-pressure cycling switch usually has to be disconnected and a jumper wire used to connect the two electrical terminals allowing the compressor to run if the system is low on charge 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 Leak Detection If the A/C system is low on a charge of refrigerant, the sources of the leak should be found and corrected Several different methods of leak detection: Visual inspection Look for oily areas formed when refrigerant leaks and some refrigerant oil is lost It is this oil that indicates a refrigerant leak Electronic leak detector Many of these units can detect both CFC-12 and HFC134a The detector will sound a tone if a leak is detected Figure 50–17 Typical electronic refrigerant leak detector Many are capable of detecting either CFC-12 or HFC-134a 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 Dye in the refrigerant Dye is added to refrigerant to help the tech spot a leak in the refrigerant system This method works well except for leaks in the evaporator, which are usually not visible Soap solution Mix a few drops of liquid soap or detergent into a small glass of water Use a small brush or spray bottle to apply the soapy solution to fittings and other areas such as the condenser and compressor If the system is empty, pressurize it with dry-nitrogen Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Figure 50–18 A black light being used to look for refrigerant leaks after a fluorescent dye was installed in the system ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The Smell Test Many air-conditioning systems form mildew inside the evaporator housing due to the moist condition that exists in this area If a “wet” smell is noticed, the mold and mildew may be the cause and a biocide will need to be used to correct the problem Leak Testing the Evaporator A quick-and-easy test to check whether the evaporator is leaking refrigerant is to remove the blower motor resistor pack The blower motor resistor pack is almost always located directly “downstream” and near the blower motor Removing the blower motor resistor pack gives access to the area near the evaporator Inserting the probe of a leak detector into this open area allows the detector to test the air close to the evaporator 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 The upper radiator hose and both heater hoses should be hot to the touch on a warm engine Failure to properly “burp” air from the cooling system after servicing can cause a lack of heat from the heater A sight glass is found on many older-model vehicles equipped with CFC-12 If the sight glass is cloudy, then the system charge is low Normal air-vent temperature for a properly operating air conditioning system is 35° to 45°F (2° to 7°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 SUMMARY (cont.) An expansion valve or orifice tube is used to allow the liquid refrigerant to expand into a gas inside the evaporator Heat is absorbed by the refrigerant as it changes state from a liquid to a gas and the evaporator becomes cold The outlet of the evaporator should be about the same temperature as the evaporator side of the orifice tube if the system is operating properly Refrigerant leaks can be detected by visual inspection, an electronic leak detector, dye, or a soap solution A partially clogged evaporator can cause a lack of cooling 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.) The temperatures of the inlet and outlet lines to and from the evaporator should be about the same if the system is fully charged 10 If the compressor clutch is cycling on and off rapidly on a cycling clutch-type system, the most common cause is low on refrigerant 11 Typical high side pressure can be estimated by adding 100 to the outside temperature 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