GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Air Conditioning

Print

SAFETY WARNINGS



Because of the the inherent dangers involved with working on air conditioning systems and R-12 refrigerant, the following safety precautions must be strictly adhered to in order to service the system safely.

  1. Avoid contact with a charged refrigeration system, even when working on another part of the air conditioning system or vehicle. If a heavy tool comes into contact with a section of tubing, or a heat exchanger, it can cause the relatively soft material to rupture.
  2.  
  3. When it is necessary to apply force to a fitting which contains refrigerant, as when checking that all system couplings are securely tightened, use a wrench on both parts of the fitting involved, if possible. This will avoid putting torque on the refrigerant tubing. (It is advisable, when possible, to use line wrenches when tightening these flare nut fittings.)
  4.  

R-12 refrigerant is a chlorofluorocarbon which when released in the atmosphere can contribute to the depletion of the ozone layer in the upper atmosphere. Ozone filters out harmful radiation from the sun.

  1. Do not attempt to discharge the system by merely loosening a filter, or removing the service valve caps and opening these valves. Precise control is possible only when using a proper A/C refrigerant recovery station. Wear protective gloves when connecting or disconnecting service gauge hoses.
  2.  

Be sure to consult the laws in your area before servicing the air conditioning system. In some states it is illegal to preform repairs involving refrigerant unless the work is done by a certified technician.

  1. Never start a system without first verifying that both service valves are properly installed, and that all fittings throughout the system are snugly connected.
  2.  
  3. Avoid applying heat to any refrigerant line or storage vessel. Never allow a refrigerant storage container to sit out in the sun, or any other sources of heat, such as a radiator.
  4.  
  5. Always wear goggles to protect your eyes when working on a system. If refrigerant contacts the eyes, it is advisable in all cases to see a physician as soon as possible.
  6.  
  7. Frostbite from liquid refrigerant should be treated by first gradually warming the area with cool water, and then gently applying petroleum jelly. A physician should be consulted.
  8.  
  9. Always keep refrigerant drum fittings capped when not in use. If the container is equipped with a safety cap to protect the valve, make sure the cap is in place when the can is not being used. Avoid sudden shock to the drum, which might occur from dropping it, or from banging a heavy tool against it. Never carry a drum in the passenger compartment of a car.
  10.  
  11. Always completely discharge the system into a suitable recovery unit before painting the vehicle (if the paint is to be baked on), or before welding anywhere near refrigerant lines.
  12.  
  13. When servicing the system, minimize the time that any refrigerant line is open to the air, in order to prevent dirt and moisture entering the system. Always replace O-rings on lines or fittings which are disconnected. Prior to installation coat, but do not soak, replacement O-rings with suitable compressor oil.
  14.  

SYSTEM INSPECTION



R-12 refrigerant is a chlorofluorocarbon which when released in the atmosphere can contribute to the depletion of the ozone layer in the upper atmosphere. Ozone filters out harmful radiation from the sun.

The easiest and often most important check for the air conditioning system consists of a visual inspection of the system components. Visually inspect the air conditioning system for refrigerant leaks, damaged compressor clutch, compressor drive belt tension and condition, plugged evaporator drain tube, blocked condenser fins, disconnected or broken wires, blown fuses, corroded connections and poor insulation.

A refrigerant leak will usually appear as an oily residue at the leakage point in the system. The oily residue soon picks up dust or dirt particulars from the surrounding air and appears greasy. Through time, this will build up and appear to be a heavy, dirt impregnated grease. Most leaks are caused by damaged or missing O-ring seals at the component connections, damaged charging valve cores or missing service gauge port caps.

For a thorough visual and operational inspection, check the following:

  1. Check the surface of the radiator and condenser for dirt, leaves and other material which might block air flow.
  2.  
  3. Check for kinks in hoses and lines. Check the system for leaks.
  4.  
  5. Make sure the drive belt is under the proper tension. When the air conditioning is operating, make sure the drive belt is free of noise or slippage.
  6.  
  7. Make sure the blower motor operates at all appropriate positions, then check for distribution of the air from all outlets with the blower on.
  8.  

Keep in mind that under conditions of high humidity, air discharged from the A/C vents may not feel as cold as expected, even if the system is operating properly. This is because the vaporized moisture in humid air retains heat more effectively than dry air, making humid air more difficult to cool.

  1. Make sure the air passage selection lever is operating correctly. Start the engine and warm it to normal operating temperature, then make sure the hot/cold selection lever is operating properly.
  2.  

REFRIGERANT LEVEL CHECKS




CAUTION
Do not attempt to charge or discharge the refrigerant system unless you have access to a recovery station and are thoroughly familiar with the system's operation and the hazards involved. The compressed refrigerant used in the air conditioning system expands and evaporates (boils) into the atmosphere at a temperature of -21.7°F (-29.8°C) or less. This will freeze any surface that it comes in contact with, including your eyes. In addition, the gas can decompose into poisonous gas in the presence of a flame.

There are two ways to check refrigerant level, depending on the model year of your vehicle.

If your vehicle is equipped with an aftermarket (non GM) air conditioner, the following checks may not apply. Contact the manufacturer for instructions on system checks.

With Sight Glass
1975-77

See Figure 1

The sight glass, for checking the refrigerant charge, is located on top of the VIR (valves in receiver). The VIR looks like a small fire extinguisher and is located on the front of the engine compartment, usually on the left side of the radiator or at the heater plenum at the firewall. This test is most effective if the outside temperature is warm; approximately 70°F (21°C) or above.



Click image to see an enlarged view

Fig. Fig. 1: VIR assembly showing sight glass and connections.

  1. Place the transmission in PARK , and apply the parking brake.
  2.  
  3. Have a helper control the accelerator pedal and run the engine to 1500 rpm (fast idle).
  4.  
  5. Set the air conditioner controls on the instrument panel for maximum cold with the blower on HIGH.
  6.  
  7. Look at the sight glass on top of the VIR. (You'll probably have to wipe it clean first). If a steady stream of bubbles is present in the sight glass, the system is low on charge. There is a good chance the system has a leak.
  8.  
  9. If no bubbles are present, the system is either full charged or completely empty. Feel the high and low pressure lines at the compressor; if no appreciable temperature difference is felt, the system is empty or nearly so.
  10.  
  11. If one hose is warm (high pressure) and the other is cold (low pressure), the system may be OK. However, you are probably making these tests because there is something wrong with your air conditioner, so proceed to the next step.
  12.  
  13. Have your helper turn the fan control on and off to operate the compressor clutch. Watch the sight glass.
  14.  
  15. If bubbles appear when the clutch is disengaged and disappear when it is engaged, the system is properly charged.
  16.  
  17. If the refrigerant takes more than 45 seconds to bubble when the clutch is disengaged, the system is more than likely overcharged. This condition will usually result in poor air conditioner operation (poor cooling) at low speeds.
  18.  
  19. Finally, check for oil streaks in the sight glass, which are a sign of trouble. Most of the time, if you see oil in the sight glass it will appear as a series of streaks, although occasionally it may be a solid stream of oil. In either case, it means that part of the charge has been lost.
  20.  

If you are sure that the system has a leak, it should be repaired as soon as possible. Leaks may allow moisture into the system, causing internal rust. The system will have to be flushed, evacuated, leak tested and recharged.

Without Sight Glass
1978 and Later

See Figure 2

The vehicles built in these years are not equipped with a sight glass in their Cycling Clutch Orifice Tube (CCOT) systems. On these vehicles it is necessary to feel the temperature difference in the inlet and outlet lines at the compressor to gauge the refrigerant level. Use the following procedure. A set of manifold gauges can be hooked up to read the refrigerant levels.


CAUTION
Always wear safety goggles when working on a system to protect the eyes. If refrigerant contacts the eye, it is advisable in all cases to see a physician as soon as possible.



Click image to see an enlarged view

Fig. Fig. 2: CCOT system components, 1978-90

  1. Connect a gauge set (engine not running). The LOW side gauge hose to the suction line near the accumulator and the HIGH side gauge hose to the liquid line or muffler. The muffler is a round shaped can about three times larger than the liquid line.
  2.  
  3. Close (clockwise) both gauge set valves.
  4.  
  5. Park the vehicle in the shade, at least 5 feet from any walls. Start the engine, set the parking brake, place the transmission in NEUTRAL and establish an idle of 1,100-2,00 rpm.
  6.  
  7. Run the air conditioning system for full cooling, in the MAX or COLD mode.
  8.  
  9. The low pressure gauge should read 5-20 psi; the high pressure gauge should indicate 120-180 psi.
  10.  


WARNING
These pressures are the norm for an ambient temperature of 70-80°F (21-27°C). Higher air temperatures along with high humidity will cause higher system pressures. At idle speed and an ambient temperature of 110°F (43°C), the high pressure reading can exceed 300 psi. Under these extreme conditions, you can keep the pressures down by directing a large electric floor fan through the condenser.

TEST GAUGES



See Figure 3

Most of the service work performed in air conditioning requires the use of a set of two gauges, one for the high (discharge) pressure side of the system, the other for the low (suction) side.

The low side gauge records both pressure and vacuum. Vacuum readings are calibrated from 0 to 30 inches Hg and the pressure graduations read from 0 to no less than 60 psi.

The high side gauge measures pressure from 0 to at least 600 psi.

Both gauges are threaded into a manifold that contains two hand shut-off valves. Proper manipulation of these valves and the use of the attached test hoses allow the user to perform the following services:

  1. Test high and low side pressures.
  2.  
  3. Remove air, moisture, and contaminated refrigerant.
  4.  

The manifold valves are designed so that they have no direct effect on gauge readings, but serve only to provide for, or cut off, flow of refrigerant through the manifold. During all testing and hook-up operations, the valves are kept in a close position to avoid disturbing the refrigeration system. DO NOT USE THE GAUGES AS A MEANS FOR DISCHARGING THE SYSTEM!



Click image to see an enlarged view

Fig. Fig. 3: Manifold gauge set and low side adapters.

DISCHARGING THE SYSTEM



R-12 refrigerant is a chlorofluorocarbon which when released in the atmosphere can contribute to the depletion of the ozone layer in the upper atmosphere. Ozone filters out harmful radiation from the sun.

Consult laws in your area before servicing the air conditioning system. In some states it is illegal to perform repairs involving refrigerant unless the work done by a certified technician

The use of refrigerant recovery systems and recycling stations makes possible the recovery and reuse of refrigerant after contaminants and moisture have been removed. If a recovery and recycling station is available, the following general procedures should be observed, in addition to the operating instructions provided by the equipment manufacturer.

  1. Check the system for pressure using the manifold gauge set. Take note, if a recovery system is used to draw refrigerant from the system that is already ruptured and open to the atmosphere, only air may be pulled into the tank.
  2.  
  3. Connect the recycling station hoses to the vehicle's air conditioning service ports and the recovery stations inlet fitting.
  4.  

Hoses should have shut-off devices or check valves within 12 in. (305mm) of the hose end to minimize the introduction of air into the recycling station and the amount of refrigerant released when the hoses are disconnected.

  1. Turn the power to the recycling station ON to start the recovery process. Allow the station to pump the refrigerant from the system until the station pressure goes into a vacuum. On some stations, the pump will be shut off automatically by a low pressure switch in it's electrical system. On other units it may be necessary to turn off the pump manually.
  2.  
  3. Once the recycling station has evacuated the system, close the station inlet valve. Then switch OFF the electrical power.
  4.  
  5. Allow the vehicle air conditioning system to remain closed for about 2 minutes. Observe the system vacuum level as shown on the gauge. If the pressure does not rise, disconnect the station's hoses.
  6.  
  7. If the system pressure rises, repeat steps 3, 4 and 5 until the vacuum level remains stable for 2 minutes.
  8.  
  9. If A/C oil is expelled during the discharge procedure, measure the amount discharged so the proper quantity of oil can be replaced when charging.
  10.  

EVACUATING/CHARGING THE SYSTEM



Evacuating and charging the air conditioning system is a combined procedure in which the lines are purged, then refrigerant is added to the system in proper quantity. Charging is always conducted through the low pressure fitting. NEVER attempt to charge the air conditioner through the high pressure side of the system.

Once again, evacuation and charging should not be attempted unless the proper equipment, such as a charging station and pump is available in order to properly service the system. If a charging station and pump is available, the following general procedures should be observed, in addition to the operating instructions provided by the manufacturer.

  1. The proper amount of fresh compressor oil must be added to the system before charging. This can be accomplished by disconnecting the suction hose and pouring the fresh oil into the hose or pipe and then reconnecting the system.
  2.  
  3. Properly connect a manifold gauge set to the vehicle, then connect the center manifold gauge hose to a vacuum pump.
  4.  
  5. Turn the vacuum pump ON and slowly open the high and the low side valves to the pump. Allow the system to evacuate for 25-30 minutes, then note the gauge readings. If the system is unable to reach 28-29 in. of vacuum, the system and vacuum pump must be checked for leaks and repaired before proceeding further.
  6.  
  7. After the system has been evacuated for at least 25 minutes, close the gauge high and low side valves , then shut the pump OFF .
  8.  
  9. Watch the low side gauge for vacuum loss. If vacuum loss is in excess of 1 in. Hg (3.38 kPa), then leak test the system, repair the leaks and return to Step 1. Before leak testing, remember to disconnect the gauge high side connector from the service port.
  10.  
  11. If after 1-3 minutes, the loss is less than 1 in. Hg (3.38 kPa), then proceed with the system charging.
  12.  
  13. Disconnect the gauge high side connection from the service port and the hose from the vacuum pump.
  14.  
  15. Engage the center manifold connection to an R-12 source. If you are using a refrigerant drum instead of a charging station, place the drum on a scale to determine the amount of refrigerant being used.
  16.  
  17. Open the source and the low side gauge valve, then monitor the weight of the drum or the rate at which the charging system is introducing the R-12 into the system.
  18.  
  19. When 1 lb. of R-12 has been added to the system, start the engine and turn the air conditioning system ON . Set the temperature level to full cold, the blower speed on high and the selector lever to the dash outlets. Under this condition, slowly draw in the remainder of the R-12 charge. The proper amount can be found on a label either on the compressor or on the evaporator case on the firewall.
  20.  
  21. When the system is charged, turn the source valve OFF and continue to run the engine for 30 seconds in order to clear the gauges and the lines
  22.  
  23. With the engine still running, carefully remove the gauge low side hose from the suction pipe service fitting. Unscrew the connection rapidly to avoid excess refrigerant loss.
  24.  


CAUTION
If the hoses of the manifold gauge set can be disconnected from the gauge, NEVER remove a hose from the gauge while the other end of the hose is still connected to the service port. Since the service valve fitting check valve is depressed by the hose connection, this would cause a complete and uncontrolled discharge of the system. Serious personal injury could be caused by the escaping R-12.

  1. Install the protective service fitting caps and hand tighten.
  2.  
  3. Turn the engine and air conditioning OFF .
  4.  
  5. If an electronic or halide leak tester is available, test the system for leaks.
  6.  
  7. If there are no leaks, perform the refrigerant level test to verify proper system charging.
  8.  

LEAK TESTING



Whenever a refrigerant leak is suspected, begin by checking for leaks at the fitting or valves. There are several methods of detecting leaks in the air conditioning system; among them the two most popular are (1) halide leak detection or the "open flame method", and (2) electronic leak-detection. Use of an electronic leak detector, if available, is preferable for ease and safety of operation.

The halide leak detector is a torch-like device which produces a yellow-green color when refrigerant is introduced into the flame at the burner. A purple or violet color indicates large amounts of refrigerant at the burner.

An electronic leak detector is a small portable electronic device with an extended probe. With the unit activated the probe is passed along those components of the system which contain refrigerant. If a leak is detected, the unit will sound an alarm signal or activate a display signal depending on the manufacturer's design. Follow the manufacturer's instructions carefully. Move the probe at approximately 1 in. (25.4mm) per second around the suspected leak area. When escaping refrigerant gas is located, the ticking or beeping signal from the detector will increase in beeps per second. If the gas is relatively concentrated, the signal will be a constant shrill.


CAUTION
Care should be taken to operate either type of detector in well ventilated areas, so as to reduce the chance of personal injury, which may result from coming in contact with the poisonous gases produced when R-12 is exposed to flame or electric spark.

If a tester is not available, perform a visual inspection and apply a soap and water solution to the questionable area or fitting. Bubbles will form to indicate a leak. Make sure to rinse the solution from the area before making repairs.

 
label.common.footer.alt.autozoneLogo