GM Metro/Sprint 1985-1993 Repair Guide

Air Conditioning System

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SAFETY WARNINGS





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 some states it is illegal to perform repairs involving refrigerant unless the work is done by a certified technician.
 
Avoid contact with a charged refrigeration system, even when working on another part of the air conditioning system or truck. If a heavy tool comes into contact with a section of copper tubing or a heat exchanger, it can easily cause the relatively soft material to rupture.
 
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 recommended that tube or line wrenches be used when tightening these flare nut fittings.
 
DO NOT attempt to discharge the system by merely loosening a fitting. Precise control is possible only when using the service gauges with an approved recovery station.
 
Always completely discharge the system before painting the truck (if the paint is to be baked on), or before welding anywhere near the refrigerant lines.
 

Any repair work to an air conditioning system should be left to a professional. DO NOT, under any circumstances, attempt to loosen or tighten any fittings or perform any work other than that outlined here.

SYSTEM INSPECTION



See Figure 1

Checking For Oil Leaks

Refrigerant leaks show up 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, especially on the hose and tubing connections. If there are oily deposits, the system may have a leak, have it checked by a qualified technician.

A small area of oil at the front of the compressor is normal and no cause for concern.

Keep The Condenser Clear

Periodically inspect the front of the condenser for bent fins or foreign material (dirt, buts, 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.

Operate The A/C System Periodically

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.

Leak Testing the System


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Fig. Fig. 1: Refrigerant leak detector

There are several methods of detecting leaks in an air conditioning system; among them, the most popular is the electronic leak detector.

An Electronic Leak Detector No. J-26934 H-10B or equivalent, 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. It is advisable to follow the manufacturer's instructions as the design and function of the detection may vary significantly.

REFRIGERANT LEVEL CHECKS



See Figure 2

A simple test to determine if the air conditioning system refrigerant level is correct can be made by observing the sight glass at the top of the receiver/dryer.



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Fig. Fig. 2: Refrigerant level check at sight glass

  1. Start the engine and run at fast idle (1,500 rpm).
  2.  
  3. Set the air conditioning controls for maximum cold and fastest blower speed.
  4.  
  5. Check the sight glass for the presence of bubbles.
  6.  
  7. Feel the high pressure side pipe leading from the compressor to the condenser and the low pressure side pipe leading from the receiver/dryer to the compressor.
  8.  
  9. If there are no bubbles, the high pressure side pipe is warm and the low pressure side pipe is cold, the system is functioning correctly.
  10.  
  11. If there are no bubbles and the high pressure side pipe is abnormally hot, there may be too much refrigerant in the system. Consult a certified air conditioning technician.
  12.  
  13. If bubbles can be seen at 1-2 second intervals, the high pressure side pipe is warm and the low pressure side pipe is fairly cold, there is an insufficient amount of refrigerant in the system. Leak test the system prior to having a certified air conditioning technician refill it with refrigerant.
  14.  
  15. If bubbles flow continuously and there is almost no difference between the high pressure side pipe and the low pressure side pipe temperature, the refrigerant in the system is almost empty. Have a certified air conditioning technician conduct an overall check of the system, repair components and refill the system with refrigerant.
  16.  

Lack of refrigerant can allow moisture to enter the system and cause major damage.

GAUGE SETS



See Figures 3, 4, 5 and 6



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Fig. Fig. 3: Refrigerant gauge set



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Fig. Fig. 4: High pressure side service port location



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Fig. Fig. 5: Low pressure side service port location



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Fig. Fig. 6: Basic components of the air conditioning system and the flow of refrigerant.

Most of the service work performed in air conditioning requires the use of a two gauge set. The gauges on the set monitor the high (head) pressure side and the low (suction) side of the system.

The low side gauge records both pressure and vacuum. Vacuum readings are calibrated from 0-30 in. Hg, and the pressure graduations read from 0-60 psi. The high side gauge measures pressure from 0-600 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:



Test high and low side pressures.
 
Remove air, moisture and/or contaminated refrigerant.
 
Purge the system of refrigerant.
 
Charge the system with refrigerant.
 

The manifold valves are designed so they have no direct effect on the gauge readings but serve only to provide for or cut off the 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 allow refrigerant to be purged into a refrigerant recovery station or to charge the air conditioning system.

When purging the system, the center service fitting hose is connected to the refrigerant recovery station and both valves are cracked (opened) slightly. This allows the refrigerant pressure to force the entire contents of the system out through the center hose. During charging, the center service fitting hose is connected to the refrigerant storage container, the valve on the high side of the manifold is closed and the valve on the low side is cracked (opened). Under these conditions, the low pressure in the evaporator will draw refrigerant from the relatively warm refrigerant storage container into the system.

DISCHARGING THE SYSTEM



See Figure 7



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Fig. Fig. 7: Refrigerant recovery and recycling center

When any refrigeration system component except the pressure cycling switch is replaced, all of the refrigerant in the 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 OFF , remove the protective cap from the low pressure side service fitting.
  2.  
  3. The refrigerant recovery station should be connected following the manufacturer's instructions.
  4.  
  5. With the low pressure side of the refrigeration system fully discharged, the high pressure side service fitting should be check for any remaining pressure.
  6.  
  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.
  8.  

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.

  1. When the system is completely discharged and the refrigerant stored in the recovery tank, the technician should measure and record the amount of refrigerant oil that was collected in the recovery system accumulator.
  2.  
  3. If the measured amount of oil is 0.5 fl. oz or more, the same amount of new refrigerant oil must be added to the system, plus any quantity in the removed parts.
  4.  
  5. To add oil, the refrigerant system low pressure side (suction) hose should be disconnected at the receiver/dryer and the correct quantity of oil should be poured into the hose.
  6.  

EVACUATING



Before charging any system it is necessary to purge the refrigerant and draw out the trapped moisture with a suitable vacuum pump. Failure to do so will result in ineffective charging and possible damage to the system.

  1. Connect the high pressure hose to the compressor delivery hose and the low pressure hose to the compressor suction hose.
  2.  
  3. Connect the center hose of the gauge set to a vacuum pump.
  4.  
  5. Operate the vacuum pump and then open the low pressure side valve of the manifold gauge set.
  6.  
  7. If the system if functioning properly, there will be an indication on the high pressure gauge. When this happens, open the high pressure side valve of the manifold gauge set.
  8.  
  9. Operate the vacuum pump for at least 10 minutes. The vacuum gauge should show a vacuum no lower than 28 in. Hg providing no leakage exists. If a leak exists, repair it.
  10.  
  11. Evacuation should be carried out for at least 15 minutes. Continue evacuating until the vacuum gauge reads 28 in. Hg, then close both valves.
  12.  
  13. Stop the vacuum pump. Observe the low pressure gauge to determine if the vacuum is holding. A vacuum drop may indicate a leak.
  14.  
  15. Disconnect the center charging hose. The system is now ready for charging.
  16.  

CHARGING




CAUTION
Never attempt to charge the system by opening the high pressure side valve while the compressor is operating. The compressor accumulating pressure can burst the refrigerant container, causing severe personal injury.

  1. Start the engine and allow it to reach operating temperature. Position the A/C control lever in the OFF position.
  2.  
  3. Using 14 oz. cans of refrigerant, in the inverted position, allow about a 1/2 lb. of refrigerant to enter the system through the low pressure side service fitting.
  4.  
  5. After 1/2 lb. of refrigerant enters the system, position the A/C control lever in the ON position (the compressor will engage) and the blower motor on HI speed; this operation will draw the remainder of the refrigerant into the system.
  6.  

To speed up the operation, position a fan in front of the condenser; the lowering of the condenser temperature will allow refrigerant to enter the system faster.

  1. When the system is charged, turn off the refrigerant source and allow the engine to run for 30 seconds to clear the lines and gauges.
  2.  
  3. With the engine running, remove the hose adapter from the low pressure side service fitting (unscrew the hose quickly to prevent refrigerant from escaping).
  4.  


CAUTION
Never remove the gauge line from the adapter when the line is connected to the system; always remove the line adapter from the service fitting first.

  1. Replace the protective caps and turn the engine off.
  2.  
  3. Using a leak detector, inspect the A/C system for leaks. If a leak is present, repair it.
  4.  

 
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