heating and air-conditioning service

© 2012 Delmar, Cengage Learning

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• Evacuate and recharge a refrigeration system in

a safe and legal manner


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


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


Air-Conditioning System Service and Diagnosis

• Visual inspection considerations– Coolant level– Condenser– Fans– Compressor drive belt– Refrigerant hoses– Wiring and hoses


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


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


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


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


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


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


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


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



• 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



• 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


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


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


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


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


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


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


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


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


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


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


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


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


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


Follow-Up• Following air-conditioning system maintenance

or repair work– System performance test should be done

• Verify success of work


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


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

heating and air-conditioning service

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