GM Caprice 1990-1993 Repair Guide

Air Conditioning System


See Figure 1

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Fig. Fig. 1: Air conditioning system

The Cycling Clutch Orifice Tube (CCOT) system includes the compressor, condenser, evaporator, an accumulator/drier with fixed orifice tube, a clutch cycling switch with or without a temperature probing capillary tube to maintain a selected comfortable temperature within the vehicle, while preventing evaporator freeze-up. Full control of the system is maintained through the use of a selector control, mounted in the dash assembly. The selector control makes use of a vacuum supply and electrical switches to operate mode doors and the blower motor. A sight glass is not used in this system and one should not be installed. When charging the system, the correct quantity of refrigerant must be installed to obtain maximum system performance.


The most important aspect of air conditioning service is the maintenance of pure and adequate charge of refrigerant in the system; likewise, the systems greatest enemy is moisture and therefore a system cannot function properly and will be damaged if leaks are not repaired in a timely manner. A refrigeration system cannot function properly if a significant percentage of the charge is lost. Refrigerant leaks can occur because of oil contamination on the hoses and lines or vibration can cause a cracking or loosening of the air conditioning fittings. As a result, the extreme operating pressures of the system force refrigerant out.


The following is a list of general precautions that should be observed while servicing the air conditioning system:

  1. Always wear safety goggles when performing any work on or around the refrigerant system.
  3. If refrigerant should contact the eyes or skin, flush the exposed area with cold water and seek medical assistance immediately.
  5. Wrap a towel around the fitting valves when connecting or disconnecting the lines.
  7. Thoroughly purge the service gauges and hoses of air and moisture before connecting them to the system. Keep them capped when not in use.
  9. Thoroughly clean any refrigerant fitting before disconnecting it, in order to minimize the entrance of dirt into the system.
  11. Plan any operation that requires opening the system beforehand in order to minimize the length of time it will be exposed to open air. Cap or seal the open ends to minimize the entrance of foreign material.
  13. Never disconnect the air conditioning gauge service line at the gauges, always disconnect the line at the service fitting, otherwise the Schrader valve in the fitting will remain open and completely discharge the system, causing possible injury or system damage.
  15. When adding oil, ensure the system has been properly discharged and pour the oil through an extremely clean and dry tube or funnel. Keep the oil capped whenever possible. Do not use oil that has not been kept tightly sealed.
  17. Use only Refrigerant 12. Purchase refrigerant intended for use only in automotive air conditioning systems. Avoid the use of Refrigerant 12 that may be packaged for another use, such as cleaning, or powering a horn, as it is impure.
  19. Using an approved recovery/recycling machine, completely evacuate a system that has been opened to replace a component, other than when isolating the compressor, or that has leaked sufficiently to draw in moisture and air. This requires evacuating air and moisture with a good vacuum pump for at least one hour.
  21. Use a wrench on both halves of a fitting that is to be disconnected, so as to avoid placing torque on any of the refrigerant lines.


Refrigerant will freeze any surface, including your eyes, that it contacts. In addition, the refrigerant changes into a poisonous gas in the presence of a flame.

  1. Operation of the air conditioning blower at all four speeds with the mode button in any position except OFF, and engagement of the compressor clutch would indicate that the electrical circuits are functioning properly. (The blower will not operate in any speed with the mode button in the OFF position.)
  3. Operation of the air conditioning control selector (mode) button to distribute air from designated outlets would indicate proper functioning.

Oil Leaks

System leaks can usually be identified as oily areas around the hoses or components. If a hose is thought to be leaking, simply grasp the hose with one hand and the line with the other and attempt to turn the line, if the line turns it is defective and must be replaced.

If it is determined that the system has a leak, it should be corrected as soon as possible. Leaks may allow moisture to enter and cause expensive repairs.

Cooling System

The air conditioning system depends on the cooling system to lower the condenser temperature and change the vapors into a liquid; therefore the cooling system must be in proper working order. The cooling system quantity and protection factor must be satisfactory. The cooling fan must also be operating properly.


For efficient operation of an air conditioned car's cooling system, the radiator cap should hold pressure which meets the manufacturer's specifications. A cap which fails to hold pressure should be replaced.


Any obstruction of or damage to the condenser fin configuration will restrict the air flow which is essential to its efficient operation. It is therefore a good rule to keep this unit clean and in proper physical shape.

Bug screens are regarded as obstructions.

Condensation Drain Tube

A molded drain tube allows the condensation which accumulates in the bottom of the evaporator housing to drain outside of the vehicle. Occasionally over time, this tube, which is generally located on the engine firewall below the evaporator housing will become obstructed and allow the evaporator housing to fill up with water (condensation). Simply unclog any obstruction in the drain tube and allow the water to drain. Be careful not to damage the evaporator core.

If this tube is obstructed, the air conditioning performance can be restricted and condensation buildup can spill over onto the vehicle's floor.


The same hand-felt temperature of the evaporator inlet pipe and the accumulator surface of an operating system would indicate a properly charged system. The system contains NO sightglass.


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

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

The high side gauge measures pressure from 0 to at last 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.
  3. Remove air, moisture, and contaminated refrigerant.
  5. Purge the system (of refrigerant).
  7. Charge the system (with refrigerant).

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 closed position to avoid disturbing the refrigeration system. The valves are opened only to purge the system of air or refrigerant and/or to charge it.


See Figures 2, 3 and 4

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Fig. Fig. 2: Air conditioning performance test

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Fig. Fig. 3: A/C low pressure side service fitting withlow pressure switch next to the fitting,located on the accumulator in right rear of engine compartment

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Fig. Fig. 4: A/C high pressure side service fitting,located on the back of the compressor.Note that the high pressure service fittingwill always be found in the thinner line;Do not charge the system through this fitting!

  1. Close (clockwise) the gauge set valves.
  3. Connect the gauge set as follows:

It is recommended that the use of an approved recovery/recycling machine only be used to perform all discharging, evacuating and recharging of the system.

    1. Locate the 2 service fittings in the air conditioning system.
    3. The low pressure fitting is located on the accumulator, connect the blue gauge hose to the fitting.
    5. The high pressure (smaller) fitting is located on the thinner line going from the accumulator to the condenser, connect the red gauge hose with special adapter to the fitting.

  1. Set the parking brake, place the transmission in N and establish an idle of 2,000 rpm.
  3. Place a high volume fan in front of the radiator grille to ensure proper airflow across the condenser.
  5. Run the air conditioning system in the MAX and COOL mode with the blower on HI . Ensure the windows and doors are closed.
  7. Insert a thermometer into the center air outlet. The thermometer should drop to approximately 45° (7°C) within a short period of time.
  9. Use the accompanying performance chart for specifications.


When replacing any of the air conditioning refrigeration components, the system must be completely discharged of refrigerant.

R-12 refrigerant is a chlorofluorocarbon which, when released into the atmosphere, can contribute to the depletion of the ozone layer in the upper atmosphere. The Ozone filters out harmful radiation from the sun.Consult the laws in your area before servicing the air conditioning system. In some states it is illegal to perform repairs involving refrigerant unless the work is done by a certified professional.If possible, an approved R-12 Recovery/Recycling machine that meets SAE standards should be employed when discharging the system. Follow the operating instructions provided with the approved equipment exactly to properly discharge the system.

Always discharge the system at the low side service fitting.

  1. With ignition turned OFF, remove protection cap from the low side service fitting on the accumulator and connect an approved Recycling/Recovery station, charging station J-23500-01.
  3. With the low side of the system fully discharged, check the high side system fitting (on the liquid line or muffler) for the remaining pressure.
  5. If some pressure is found, attempt to discharge the high side using the same procedure as was used for the low side. (This condition indicates a restriction on the high side and the cause must be diagnosed and corrected before evacuating and charging the system.
  7. When the system is completely discharged (no vapor escaping with hose fully tightened down), measure, record amount, and discard the collected refrigerant oil. If the measured quantity is 1 / 2 fl. oz. (15ml) or more, this amount of new 525 viscosity refrigerant oil must be added to the system, plus any quantity in removed parts before system evacuation and charging with R-12.


Adding oil to the air conditioning system should take place after discharging and before evacuation procedures by removing the refrigeration suction hose at the accumulator outlet pipe connection, pouring the correct quantity of new refrigerant oil into the hose or pipe and then properly reconnecting the hose to the pipe. The R-4 compressor system requires 6 fl. oz. (180ml) of 525 viscosity refrigerant oil.

  1. Remove only the accumulator.
  3. Drain, measure and record quantity of oil in the accumulator.

It is not necessary to remove and drain the compressor because the compressor only retains a minimum quantity of oil.