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Heating and Air-Conditioning Service

Heating and Air-Conditioning Service. Chapter 36. Objectives. Locate obvious problems in heating and air-conditioning systems with a visual inspection Test air conditioner efficiency and pressures Locate leaks in the refrigeration system Diagnose and repair problem components

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Heating and Air-Conditioning Service

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  1. Heating and Air-Conditioning Service Chapter 36

  2. Objectives • Locate obvious problems in heating and air-conditioning systems with a visual inspection • Test air conditioner efficiency and pressures • Locate leaks in the refrigeration system • Diagnose and repair problem components • Evacuate and recharge a refrigeration system in a safe and legal manner

  3. Heater Service • Complaints are usually related to coolant leaks or inappropriate temperatures for the season • Heater flow can be checked by feeling hoses at inlet and outlet to heater core • Heater core replacement • Leaking heater core replaced • Heater housing must be removed

  4. Air-Conditioning Service • Challenging and rewarding specialty area • Technicians must be licensed to service all air- conditioning systems • Air-conditioning safety • Always the highest priority • Be sure to use the correct refrigerant

  5. Air-Conditioning System Service and Diagnosis • Visual inspection considerations • Coolant level • Condenser • Fans • Compressor drive belt • Refrigerant hoses • Wiring and hoses

  6. System Performance Test • Includes: • Locating specifications • Identifying the refrigerant type • Connecting pressure gauges • Measuring outlet duct temperatures • Refrigerant identifier • Determines the refrigerant type is correct • Testing air-conditioning efficiency • Set control to maximum cool • Set blower to high

  7. Pressure Testing • Pressure gauge set • Used to measure pressures in the system • Service valves • Discharge service valve is on the output side of the compressor on the high side • Suction service valve on the inlet to the compressor on the low side • Connecting the gauges • Use quick-disconnect couplings on the refrigerant machine

  8. Static Pressure Reading • Static pressure • Pressure reading in the system when it is not operating • High- and low-side pressure will be equal when there is no refrigerant movement • Pressure is equal when in a confined area

  9. Static Pressure Reading (cont’d.) • Reading system pressure • When you start the engine and turn on the air- conditioning, the low side pressure will drop • Inspect the sight glass if the system has one • System operating pressure • Humidity affects system pressure • Pressure test results • Can point you to possible problems

  10. Static Pressure Reading (cont’d.) • System operation quick check • Feel the temperature • Check for hot and cold • Air distribution system inspection • Low side is cool but system is not cooling • Problem could be with air door or panel controls • Air discharge temperatures • Most deal with temperatures on Fahrenheit scale • Air-conditioning system noises • Some are normal and some indicate problems

  11. Diagnosing HVAC Electronic Problems • Most automatic temperature control systems have self-diagnostic capability • HVAC module controls compressor clutch circuit • Electronic control problems with an HVAC system are often due to an electromechanical cause • Be certain all mechanical parts of the system are operating correctly

  12. Air Distribution System Diagnosis • Air distribution system problems • Often the cause of customer complaints • Automatic temperature control system diagnosis • Automatic temperature control (ATC) systems differ between manufacturers • Electric motor actuators • Manual and automatic electric air-conditioning system actuators are similar • Door problems • Air door and blend door

  13. Air Distribution System Diagnosis (cont’d.) • Mode door • Directs air in response to the commanded temperature from the control head • Fresh air setting • More efficient when temperature inside the vehicle is above outside ambient air • Recirculating setting • Allows some fresh air to enter • Cabin air filters • Cleans circulated air

  14. Air Distribution System Diagnosis (cont’d.) • Ion generators • Used to purify air • Blower and blower control module problems • Heat generated between brushes can shorten motor life • Replacing a blower • Be aware that the direction of some motors can be reversed • Diagnosing an inoperable blower • Most likely causes electrical wiring or controls

  15. Air Distribution System Diagnosis (cont’d.) • Blower power module problems • Do an amp draw test on the blower motor • Restricted airflow • Can be due to a plugged cabin air filter or an oily evaporator that has accumulated dust • Sensor testing • Input sensor should hold tissue and drop it off when it goes off • Ambient sensor problems • Possible culprit when no cold air comes from vents

  16. Leak Detection • Methods • Soapy water • UV dye leak detection • Colored dye • Electronic leak detection • O-rings and seals • Threaded fittings and block fittings are often sealed with O-rings

  17. Common Air-Conditioning Component Problems • Prior to component removal • Capture all of the refrigerant • Accumulator or receiver/dryer service • Receiver/dryer or accumulator • Should be replaced whenever its systems has been leaking, left empty, or left open for a long time

  18. Refrigerant Oil • Lubricates compressor, gaskets, seals, and expansion valve • Choosing the right oil • The oil must be compatible with the refrigerant • Be sure to use the correct type and viscosity • In an orifice tube/accumulator system, most of the refrigerant in the evaporator will be liquid

  19. Evaporator Problems • Some manufacturers put a layer of foam on the outside of the passenger side of an evaporator • Prevents water from being blown on passengers • Some technicians spray Lysol on the foam if it mildews • If an evaporator leaks, it must be replaced • Usually located within the dashboard • Replacing it can be time consuming

  20. Thermal Expansion Valve or Orifice Tube Problems • Orifice tube system cycles the clutch to control refrigerant flow through the system • Expansion valve • When an expansion valve is not working correctly, system pressures will not be as expected • Common problem: failure of the sensing bulb • Orifice tube service • Accumulator should feel cold and sweaty • Orifice tube is easily checked and replaced

  21. Compressor Service • Compressors are relatively reliable • Usually fail as a result of a leak • Replacing a compressor • Be sure the new one has the correct part number • Refrigerant filters • Can be added • Flushing an air-conditioning system • Aftermarket compressor manufacturers require solvent flushing

  22. Compressor Service (cont’d.) • Clutch problems • Check for source voltage • Clutch failures • Several reasons (e.g., excessive air gap) • Clutch replacement • New clutch assemblies are commonly available • Clutch plate is removed first • Compressor shaft seal replacement • Special tools are available

  23. Evacuating and Recharging • Two additional hoses attached to center connection on manifold set • Refrigerant supply tank hookup and remote vacuum • Refrigerant identification • Before evacuating refrigerant, be certain it is the same refrigerant as in tank reservoir

  24. Vacuuming a System • Vacuuming dries moisture and helps the efficiency of the system • Must have a high-quality vacuum pump to remove most moisture from the system • For best results, try to achieve at least 29.5" of vacuum and always evacuate for at least 20 minutes • Required time for factory evacuations is only 45 seconds • Protect a vacuum pump by changing its oil every ten hours or less

  25. Evacuate the System • Evacuation and recharging • Done with engine off by connecting center hose to both service ports and opening both valves • Connect the center service hose to vacuum pump • When vacuum pump starts, system pressure drops • Following evacuation close all valves and shut off the pump • Replacing refrigerant oil • Refrigerant charge is 10% low: pressure might be too low to circulate oil

  26. Air-Conditioning Service Equipment • Dual pass machine • First recover then recycle • Single pass machine • No need to ever charge with vapor • Machine recovers the refrigerant and recycles it during a 15-minute minimum vacuum cycle

  27. Refrigerant Charging • After evacuation process is complete, refill the system with refrigerant • Refrigerant charge amount is critical and each system is different • Evaporator and accumulator temperature tests • Evaporator inlet and outlet temperature test • Accumulator inlet and outlet temperature test • Incorrect refrigerant fill • Pressure gauge readings are not dependable • Scale may not be accurate

  28. Refrigerant Charging (cont’d.) • Determine the correct refrigerant amount • Usually found on an under-hood label • Refilling through the low side • Liquid refrigerant entering the low side can damage the compressor • Completing the refill • System should begin to operate normally when the fill level is about a half pound less than full

  29. Follow-Up • Following air-conditioning system maintenance or repair work • System performance test should be done • Verify success of work

  30. Refrigerant Storage • Commercial refrigerants • Typically sold in 30 lb containers • Resemble propane bottles • Disposable • Have blow-off protection • Different refrigerants should not be mixed • This will form a new chemical compound • Can cause higher pressures, resulting in damage

  31. Recycling and Retrofit • Retrofitting an R-12 system is possible • There are some drawbacks • Manufacturers have kits • Go back ten model years • Items a retrofit might require • Compressor front seal • Large condenser • Desiccant • Extra cooling fan • Hoses and O-rings

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