GM Prizm/Nova 1985-1993 Repair Guide

Air Conditioning



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

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

There are two particular hazards associated with air conditioning systems and they both relate to refrigerant gas.

The refrigerant (generic designation: R-12, trade name: Freon, a registered trademark of the DuPont Co.) is an extremely cold substance. When exposed to air, it will instantly freeze any surface it comes in contact with, including your eyes.

The other hazard relates to fire. Although normally non-toxic, refrigerant gas becomes highly poisonous in the presence of an open flame. One good whiff of the vapor formed by refrigerant can be fatal. Keep all forms of fire (including cigarettes) well clear of the air conditioning system.

Further, since it has been established that the chemicals in R-12 (dichlorodifluoromethane) contribute to the damage occurring in the upper atmosphere, sophisticated recovery equipment will be necessary to prevent the release of this gas when working on an air conditioning system. DO NOT, under any circumstances, attempt to loosen or tighten any fittings or perform any work other than that outlined here.


A lot of A/C problems can be avoided by simply running the air conditioner at least once a week, regardless of the season. simply let the system run for at least 5 minutes a week (even in the winter), and you'll keep the internal parts lubricated as well as preventing the hoses from hardening.

Checking For Oil Leaks

Refrigerant leaks show up only as oily areas on the various components because the compressor oil is transported around the entire system along with the refrigerant. Look for oily spots on all the hoses and lines, and especially on the hose and tube connections. If there are oily deposits, the system may have a leak, and you should have it checked by a qualified repairman.

A small area of oil on the front of the compressor is normal and no cause for alarm.

Check the Compressor Belt

The compressor drive belt should be checked frequently for tension and condition. Refer to Drive Belts in this section.

Keep the Condenser Clear

The condenser is mounted in front of the radiator. It serves to remove heat from the air conditioning system and cool the refrigerant. Proper air flow through the condenser is critical to the operation of the system.

Periodically inspect the front of the condenser for bent fins or foreign material (dirt, bugs, leaves, etc..). If any cooling fins are bent, straighten them carefully with needle nose pliers. You can remove any debris with a stiff bristle brush or hose.

Refrigerant Level Check

See Figures 1 and 2

The first order of business when checking the refrigerant is to find the sight glass. It is located in the head of the receiver/drier. On Novas, it's located to the left of the radiator, just behind the left headlights. On the Prizm, it's still behind the headlight, but in front of the condenser. Once you've found it, wipe it clean and proceed as follows:

  1. With the engine and the air conditioning system running, look for the flow of refrigerant through the sight glass. If the air conditioner is working properly, you'll be able to see a continuous flow of clear refrigerant through the sight glass, with perhaps an occasional bubble at very high temperatures.

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Fig. Fig. 1: Location of receiver-drier and sight glass on 1989-92 Prizm

  1. Cycle the air conditioner on and off to make sure what you are seeing is refrigerant. Since the refrigerant is clear, it is possible to mistake a completely discharged system for one that is fully charged. Turn the system off and watch the sight glass. If there is refrigerant in the system, you'll see bubbles during the off cycle. If you observe no bubbles when the system is running and the air flow from the unit in the car is delivering cold air, everything is OK.
  3. If you observe bubbles in the sight glass while the system is operating, the system is low on refrigerant. Have it checked by a professional.

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Fig. Fig. 2: Oil streaks (A), constant bubbles (B) or foam (C) indicate there is not enough refrigerant in the system. Occasional bubbles during initial operation is normal. A clear sight glass indicates a proper charge of refrigerant or no refrigerant at all, which can be determined by the presence of cold air at the outlets in the car. If the glass is clouded with a milky white substance, have the receiver/drier checked professionally

  1. Oil streaks in the sight glass are an indication of trouble. Most of the time, if you see oil in the sight glass, it will appear as 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. This is almost always accompanied by a reduction in cold air output within the car.


See Figure 3

Before attempting any charge-related work, you will need a set of A/C gauges. These are generally available from good parts suppliers and automotive tool suppliers. Generally described, this tool is a set of two gauges and three hoses. By connecting the proper hoses to the car's system, the gauges can be used to see the air conditioning system at work. The gauge set is also used to discharge and recharge the system.

Additionally, if a component must be removed from the system, a vacuum pump will be needed to evacuate (draw vacuum) within the system to eliminate any moisture which has entered during repairs. These pumps can be purchased outright; many find it easier to rent one from a supplier on an as-needed basis.

Refrigerant will be needed; make sure you purchase enough meet the capacity of the system. Since the refrigerant is measured by weight (generally in ounces), you'll need a small scale to weigh the refrigerant container as the system is recharged.

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Fig. Fig. 3: A typical set of manifold gauges for the air conditioning system


See Figures 4, 5 and 6

Wear protective goggles and gloves before proceeding with repairs.

Connecting and disconnecting the gauges should always be done with the engine off to prevent injury from moving parts. To hook up the gauges, first make sure that the valves on the gauges are turned to the closed (off) position. The hose from the low-pressure gauge will attach to the low pressure side (suction) of the A/C system.

The Prizm has this connection on the compressor; it's labeled S. The fuel-injected Nova's low pressure connector is found in the piping on the firewall - it's the line that does NOT connect to the receiver-drier. Carbureted Novas have the low pressure connection in a vertical section of the A/C tubing on the right side of the engine near the fender; it's the line that couples to another short piece running to the compressor.

Discharging and Recovering Refrigerant

When any refrigeration system component except the pressure cycling switch is replaced, all of the Refrigerant-12 in the refrigeration system must be completely discharged and recovered by using an approved air conditioning refrigerant recovery system. The system must always be discharged at the low-pressure side service fitting to control the loss of refrigerant oil. Oil loss will occur if the high-pressure side service fitting is used.

  1. With the ignition switch in the OFF position, remove the protective cap from the low-pressure side service fitting.
  3. The refrigerant recovery station should be connected, following the equipment manufacturer's instructions.
  5. With the low-pressure side of the refrigeration system fully discharged, the high-pressure side service fitting should be checked for any remaining pressure.
  7. If refrigerant under pressure remains in the high-pressure side of the system, an attempt should be made to discharge the high-pressure side of the system by using the same procedure as used for the low-pressure side service fitting. Noticeable residual pressure in the system indicates a restriction in the high-pressure side of the system. The cause for this pressure must be diagnosed and corrected before evacuating and charging the system.
  9. When the system is completely discharged and the refrigerant stored in the recovery tank, the technician should measure, record the amount and discard the refrigerant oil that was collected in the recovery system accumulator.
  11. If the measured quantity of oil is 0.5 fl. oz. (15 ml) or more, the same amount of new 525 viscosity refrigerant oil must be added to the system, plus any quantity in the removed parts. This must be done before evacuating the system and charging it with Refrigerant-12. For the specific quantity of oil normally retained in the removed part, refer to Refrigerant Oil Distribution later in this section.

Adding Oil

Refrigerant oil must be added after the refrigeration system has been discharged and before it is evacuated. To add oil, the refrigeration system suction hose should be disconnected at the receiver/dryer outlet pipe connection. The correct quantity should be poured into the hose. The hose should then be connected to the pipe. For specific quantity instructions, refer to Refrigerant Oil Distribution later in this section.

Refrigerant Oil Distribution

The refrigeration system requires a total of 6.0 fl.oz. (180 ml) of 525 viscosity refrigerant oil. New oil quantities must be added to the system during component replacement.

With no signs of excessive oil leakage, oil should be added in the following prescribed manner:

  1. If the compressor is removed, drain the oil from both the defective compressor and the new replacement compressor. Measure the amount removed for the defective compressor. If the measure amount is less than 1.0 fl.oz. (30 ml), add 2.0 fl.oz. (60 ml) to the new replacement compressor. If more than 1.0 fl.oz. (30 ml), is drained from the defective compressor, add the same amount to the new compressor.
  3. If the evaporator is removed, 3.0 fl.oz. (90 ml) of new oil must be added to the system.
  5. If the condenser is removed, drain and measure the oil in it. If more than 0.5 fl.oz. (15 ml) is collected, add the same amount to the refrigeration system.
  7. If the receiver/drier is removed, 3.5 fl.oz. (100 ml) of oil must be added to replace the oil trapped in the desiccant of the original receiver/drier.

With signs of excessive oil leakage, only the receiver/drier should be removed. The oil in the receiver/drier should be drained, measured and recorded. It is not necessary to remove and drain the compressor because it retains only a minimum quantity of oil. With signs of excessive oil leakage, oil should be added in the following prescribed manner:

  1. If less than 3.0 fl.oz. (90 ml) of oil was retained in the receiver/drier, 3.0 fl.oz. (90 ml) of new oil should be added to the system.
  3. If more than 3.0 fl.oz. (90 ml) of oil was retained, an equal amount of new oil should be added.

Refrigerant Loss from an Abrupt Leak

If the refrigerant charge is abruptly lost due to a large refrigerant leak, approximately 3.0 fl.oz. (90 ml) of refrigerant oil will be carried out of the system suspended in the refrigerant. Any failure that causes an abrupt refrigerant discharge will result in this oil loss. Failures that allow the refrigerant to seep or bleed off over time do not cause this oil loss.

Upon replacement of a component which caused a large refrigerant leak, add 3.0 fl.oz. (90 ml) of new 525 viscosity refrigerant oil plus the required amount of oil for the particular component.

Add the oil directly to the replaced component if possible. If the oil cannot easily be added to the replaced part, add the oil to the receiver/drier.


The charging instructions provided with the charging station should be adhered to with the following exceptions:

  1. The high-pressure line should not be connected to the refrigeration system.
  3. The high-pressure valve on the charging station should remain closed at all times.
  5. The entire evacuating and charging procedure should be done through the low-pressure side service fitting.

Following these procedures will prevent high-pressure side system pressure from getting to the charging station. This fact can become crucial if an error is made in the valve sequence during the compressor operation to pull in the Refrigerant-12.

Refrigerant Drum Method

The Refrigerant-12 drum should be placed on a scale and the total weight noted before charging. During charging, the scale should be monitored to determine the amount of refrigerant used.

The low-pressure gage of the J 23575-01 Manifold Gage Set should be connected at the low-pressure side service fitting. The high-pressure gage should be connected to the J 34119 Vacuum Pump. The J 23575-01 Manifold Gage Set center gage hose should be connected to the Refrigerant-12 drum. A J 23390 Control Valve must be connected to the 5.4 kg (12 lb.) drum to control the flow of refrigerant. The 13.6 kg (30lb.) drum incorporates its own control valve.

To begin evacuating the refrigeration system, the high-pressure side and low-pressure side gage valves should be opened slowly and the vacuum pump should be started. The system should be pumped until the low-pressure side gage reaches a vacuum reading of 94.6-97.9 kPa (28-29 in. Hg) at sea level. For each 305m (1,000 ft.) above sea level, this specification should be lowered by 3.38 kPa (1.0 inch). At 1,525m (5,000 ft.) elevation, a vacuum reading of only 77.7-81.1 kPa (23-24 in. Hg) is required.

If the specified vacuum cannot be reached, the vacuum control valve should be closed and the pump should be shut off. Then the pump and connection should be checked for a leak.

When the low-pressure side gage reaches the specified vacuum reading, the system is fully evacuated. The high-pressure side gage valve should be closed and the vacuum pump should be shut off.

The low-pressure side gage should be watched to be sure the vacuum holds for five minutes. If vacuum is held for five minutes, the vacuum hose should be disconnected at the high-pressure side gage and charging should begin. If vacuum does not hold for five minutes, the system should be charged with 0.23 kg (0.5 lb.) of Refrigerant-12 and a check made for refrigerant leaks. The system should be discharged and the refrigerant recovered before repairing the leak(s). Then the evacuation procedure should be repeated.


To prepare for charging the refrigeration system, the engine should be started and run until it reaches operating temperature. The air conditioning mode lever should be in the OFF position.

With the engine at operating temperature and the Refrigerant-12 drum inverted, the refrigerant source valve should be opened to allow 0.23 kg (0.5 lb.) of liquid Refrigerant-12 to flow into the system through the low-pressure side service fitting.

As soon as this quantity of refrigerant enters the refrigeration system, the compressor should be engaged by pressing the A/C switch and moving the blower speed switch to any position by OFF. This will draw in the remainder of the total refrigerant charge. The total charge is 1.59 kg (3.50 lbs.).

Charging speed can be increased by placing a large volume fan in front of the vehicle to pass more air over the condenser. If condenser temperature is maintained below the temperature of the charging drum, Refrigerant-12 will enter the system more rapidly.

When the full charge is added, the Refrigerant-12 source valve should be turned off and the engine allowed to run for 30 seconds to clear the lines and gages.

A gage line should never be removed from its adapter when the line is connected to the refrigeration system. The line adapter from the service fitting always should be removed to disconnect a line. The charging hose at the gage set should not be removed while the hose is attached to the low-pressure side service fitting. This may result in complete discharge of the system and may cause personal injury from escaping Refrigerant-12.

With the engine running, the low-pressure side charging hose adapter should be removed from the low-pressure side service fitting. It must be unscrewed rapidly to avoid releasing excessive refrigerant from the system.

After replacing the protective cap on the low-pressure side service fitting and turning OFF the engine, a leak test should be performed using the J 29547 Electronic Leak Detector. With the refrigeration system fully charged and leak-tested, the air conditioning system should be tested to ensure proper performance. Refer to Refrigeration System Checks earlier in this section.

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Fig. Fig. 4: Air conditioning refrigerant recovery/recycling station J38100-B or C, component locations

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Fig. Fig. 5: Air conditioning refrigerant recovery/recycling station hookup

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Fig. Fig. 6: Charging the air conditioning system