Volkswagen Front Wheel Drive 1974-1989 Repair Guide

Air Conditioning System

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SAFETY WARNINGS




CAUTION
Do not discharge the refrigerant from the air conditioning system into the atmosphere.

The R-12 refrigerant used in all models is a chlorofluorocarbon that destroys the earth's ozone layer in the upper atmosphere. Ozone filters out harmful radiation from the sun. In most states, it is against the law to discharge an air conditioning system into the atmosphere and air conditioning service that involves R-12 can only be legally performed by certified technicians. Make sure the proper recovery equipment is available before servicing the air conditioning system. Volkswagen recommends the Kent-Moore ACR3 recovery/recycling unit or an equivalent system.



Always wear eye protection when working with R-12.
 
Make sure R-12 does not come in contact with skin or eyes.
 
If contact occurs, flush with cool water for 15 minutes and seek medical attention.
 
Avoid breathing fumes when using flame-type leak detectors. R-12 becomes a poisonous gas when in contact with open flame.
 
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 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 line or flare nut wrench on both parts of the fitting involved. This will avoid twisting the tubing.
 
Avoid applying heat to any refrigerant line or storage vessel. Never allow a refrigerant storage container to sit out in the sun, or near any other source of heat, such as a radiator.
 
Always keep refrigerant can fittings capped when not in use. Avoid sudden shock to the can which might occur from dropping it, or from banging a heavy tool against it. Never carry a can in the passenger compartment of a vehicle.
 
Always completely discharge the system before painting the vehicle (if the paint is to be baked on), or before welding anywhere near the refrigerant lines.
 
Do not use any other type of refrigerant in an R-12 system. This can cause component failure and usually results in having to replace the entire system. This is expensive!
 

SYSTEM INSPECTION



Even if you are not properly equipped to service an air conditioning system, there are some simple things to check that may avoid expensive problems later. The most important aspect of air conditioning service is the maintenance of a full charge of refrigerant in the system. A refrigeration system cannot function properly if a significant percentage of the charge is lost. The refrigerant also carries the lubricating oil for the entire system. This means that even if there is enough of a charge for the system to provide effective cooling, there may not be enough oil to properly protect the system.

Leaks in the air conditioning system usually occur at the compressor shaft seals. The compressor is the major moving part and is subjected to engine vibrations, temperature extremes and great pressure differentials. The greatest damage to these seals occurs when the system is not used for long periods. When the compressor is finally turned on, the rubber seals are stiff and dry and can easily form tiny cracks. The seals leak slowly at first but eventually system pressure drops enough for the low pressure safety switch to prevent compressor operation.

One way Volkswagen prolongs compressor seal life is to make the compressor run any time the defroster is in use. This not only assures that the compressor will be run throughout the year, it also makes the defroster very effective by drying the air being blown at the windshield. Since the system is in use all year long, it is important that a full charge be maintained at all times. Fortunately no special equipment is required to inspect the condition of the system and to check the refrigerant level.

Engine Cooling System

Under extreme conditions, it may take as much as 10 horsepower to run the air conditioner compressor. If the engine is required to work that much harder, the cooling system must be up to the job. Make sure the water pump belt is properly adjusted and that there are no leaks in the system. Pressure test the system and the reservoir cap if possible. Just as important is the condition of the antifreeze.

In order to prevent heater core freeze-up during air conditioner operation, it is necessary to maintain permanent type antifreeze protection of +15°F (-9°C) or lower. Protection to -15°F (-26°C) is ideal since this protection also supplies sufficient corrosion inhibitors for the engine cooling system. Make sure the antifreeze is not in use longer than recommended by the manufacturer (usually 2-3 years).

Condenser

The condenser is in front of the engine's radiator. Any obstruction of or damage to the condenser will restrict the air flow that carries away the heat. If many of the fins are crushed or if they are clogged with bugs or dirt, it will take a long time to cool off the inside of the vehicle. Blowing compressed air through the fins from behind the radiator will usually also clean the condenser. If the front of the vehicle is fitted with a bra or other type of bug screen, air conditioner efficiency is usually somewhat decreased.

Condensation Drain Tube

This molded tube drains out the water that condenses from the air into the evaporator housing inside the vehicle. The tube usually exits into the engine compartment through the firewall. If this tube is obstructed, the evaporator housing will fill with water and eventually the air conditioner vents will emit fog or a fine mist when the air conditioner is running. Another sign of a clogged drain tube is a bad odor when using the air conditioner. This is caused by bacteria growth in the water sitting in the evaporator housing. There are some products available to deal with this problem but they aren't easy to find in auto parts stores.

REFRIGERANT LEVEL CHECK



See Figure 1

You can safely make a few simple checks to determine if your air conditioning system needs service. The tests work best if the temperature is warm, about 70°F (21°C).

This test is for the factory installed air conditioning system only. Aftermarket air conditioner testing procedures may be different. If in doubt, contact the manufacturer of your particular unit.

  1. Place the automatic transaxle in Park or the manual transaxle in Neutral. Set the parking brake.
  2.  
  3. Run the engine at a fast idle, about 2500 rpm.
  4.  
  5. Set the air conditioning controls for maximum cold and the highest fan speed.
  6.  
  7. Locate the sight glass and wipe it clean. The sight glass is located either in the high pressure tube between the high pressure service valve and the receiver drier or on top of the receiver drier itself.
  8.  
  9. If you see foam or lots of bubbles, the system is low on refrigerant and should be recharged. There is probably a leak in the system but it may not be serious enough to require repairs at this point.
  10.  
  11. If there are no bubbles in the sight glass and air coming from the vents is warm, the charge is very low and the system needs a full service. If there are few or no bubbles and the vent air is cold, the charge is OK.
  12.  
  13. Have an assistant in the vehicle 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. If the refrigerant takes more than 45 seconds to bubble when the clutch is disengaged, the system is overcharged. This usually causes poor cooling at low speeds.
  16.  



Click image to see an enlarged view

Fig. Fig. 1: The refrigerant sight glass can be used to check for proper system charge

GAUGE SETS



See Figure 2

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 in.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 the use of appropriate service equipment allows the user to perform the following services:

  1. Read high and low side pressures.
  2.  
  3. Remove air, moisture, and contaminated refrigerant.
  4.  
  5. Purge the system of refrigerant.
  6.  
  7. Charge the system with refrigerant and the correct amount of oil.
  8.  

The manifold valves are designed so that they have no direct effect on gauge readings but provide precise flow control of refrigerant through the manifold. During all testing and hook-up operations, the valves are kept closed to avoid disturbing the refrigeration system. The valves are opened only to read pressures, to purge the system or to charge it.



Click image to see an enlarged view

Fig. Fig. 2: Manifold gauge set used to service air conditioning systems

DISCHARGING THE SYSTEM




CAUTION
Do not discharge the refrigerant from the air conditioning system into the atmosphere.

The R-12 refrigerant used in all models is a chlorofluorocarbon that destroys the earth's ozone layer in the upper atmosphere. Ozone filters out harmful radiation from the sun. In most states, it is against the law to discharge an air conditioning system into the atmosphere. In some states, air conditioning service can only be legally performed by certified technicians at properly equipped shops. Make sure the proper recovery/recycling equipment is available before servicing the air conditioning system. Volkswagen recommends the Kent-Moore ACR3 recovery/recycling unit or an equivalent system.

  1. Check for any special instructions on the recovery equipment. If they are different from what is shown here, follow those instructions.
  2.  
  3. Connect the center hose of the gauge manifold set to the recovery unit.
  4.  
  5. Remove the caps from the service valves or clean the valves if the caps are missing.
  6.  
  7. Make sure both gauge set manifold valves are closed. Connect the low pressure hose of the recovery equipment to the low pressure service valve. The return line with this valve is the line without the sight glass.
  8.  
  9. Connect the high pressure hose to the high pressure service valve.
  10.  
  11. Slowly open both valves and allow the system to discharge into the recovery equipment.
  12.  
  13. When the system is fully discharged, close the valves and remove the hoses.
  14.  
  15. Be sure to install the caps again. All fittings must remain closed as much as possible to avoid moisture getting into the system. Disconnect the wire to the compressor clutch to avoid accidently running the compressor.
  16.  

EVACUATING THE SYSTEM



  1. With the manifold gauges connected and the system discharged, close both valves and connect the center service hose to the inlet fitting of the vacuum pump.
  2.  
  3. Turn both manifold valves to the wide open position.
  4.  
  5. Start the pump and note the low side gauge reading.
  6.  
  7. Operate the pump for a minimum of 30 minutes after the lowest observed gauge reading.
  8.  
  9. Close the valves, stop the pump and note the low side gauge reading. The needle should remain stationary at the point at which the pump was turned off. If the needle starts to drop and does not stop, there is a leak and the system will not hold a charge.
  10.  
  11. If the needle remains stationary for 3 to 5 minutes, open the manifold valves and run the pump for at least 30 minutes more.
  12.  
  13. Close both valves and stop the pump. The system is now ready for charging.
  14.  

CHARGING THE SYSTEM



If the proper recovery/recycling equipment has been used to discharge the system, follow the instructions with that equipment for charging the system. The procedure shown here is for charging the system with individual cans of R-12. Be sure to read and follow the safety precautions outlined at the beginning of the air conditioning section.

  1. With the valves closed, connect the center hose of the manifold set to the refrigerant can opener valve.
  2.  
  3. Make sure the can opener valve is unscrewed (the needle is raised) and connect the valve to the can. Open the can by screwing the valve in to puncture the can with the needle.
  4.  
  5. Momentarily loosen the center hose fitting at the pressure gauge, allowing refrigerant to purge the hose of air.
  6.  
  7. Open the low side gauge set valve and the can valve.
  8.  
  9. Start the engine and turn the air conditioner to the maximum cooling mode. The compressor will operate and pull refrigerant gas into the system. If more than one can of refrigerant is needed, close the can valve and gauge set low side valve when the can is empty and connect a new can to the opener. The frost line on the outside of the can will indicate how much is left.
  10.  
  11. When the charging process has been completed, close the valves and run the system for at least five minutes to allow it to normalize.
  12.  
  13. Check the pressures again and if all is correct, remove the hoses. Screw the covers onto both service valves.
  14.  

LEAK TESTING



If you don't have the proper service equipment, you can still partially leak check the system. With the engine not running, look at each connection in the system for signs of oil leakage. This will appear as an accumulation of dirt where everything else is clean, or may even be wet with oil. Check for signs of leaking at the clutch end of the compressor; streaks radiating out from the center of the shaft. If there is enough of a charge for the compressor to run, apply a soapy water solution to each connection one at a time with the system operating (don't try to check the compressor this way). If you are adding refrigerant, use R-12 with a dye included. Any leaks will show up quickly.

 
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