R-134a SYSTEMSGeneral Information
Some 1992-93 and all 1994-95 vehicles are equipped with a refrigerant (R-134a) that is incompatible with the older R-12 or Freon®. This newer refrigerant is NOT available commercially in most areas, and it may be illegal to service a vehicle with this refrigerant. If you have a vehicle equipped with R-134a, it should be taken to a qualified technician for all A/C service.
Some 1992-93 vehicles equipped with the 3.0L engine, and all 1994-95 vehicles are using R-134a refrigerant, rather than the conventional R-12 refrigerant. The new R-134a refrigerant is not harmful to the ozone layer of the atmosphere. It has many of the same properties as the old type of refrigerant and is similar in both form and function. These two refrigerants are not interchangeable with one another. Therefore, do not mix the two types of refrigerant, the tools used in servicing the air conditioning system, or component replacement parts from these two types of air conditioning systems. Failure to follow these guidelines will result in damage to the vehicle air conditioning system, and may also result in personal injury to the individual.System Identification
In order to determine which type of system your vehicle has, an identification data plate is located on the major system components. If the system components have YELLOW R-134a non-cfc tags, then the system requires R-134a refrigerant. These systems can also be identified by a gold-colored air conditioning compressor clutch and green-colored O-rings used throughout the system.
GENERAL SERVICING PROCEDURES
It is recommended, and possibly required by law, that a qualified technician perform the following services.
The most important aspect of air conditioning service is the maintenance of a pure and adequate charge of refrigerant in the system. A refrigeration system cannot function properly if a significant percentage of the charge is lost. Leaks are common because the severe vibration encountered underhood in an automobile can easily cause a sufficient cracking or loosening of the air conditioning fittings. As a result, the extreme operating pressures of the system force refrigerant out.
The problem can be understood by considering what happens to the system as it is operated with a continuous leak. Because the expansion valve regulates the flow of refrigerant to the evaporator, the level of refrigerant there is fairly constant. The receiver/drier stores any excess refrigerant, so a loss will first appear as a reduction in the level of liquid. As this level nears the bottom of the vessel, some refrigerant vapor bubbles will begin to appear in the stream of liquid supplied to the expansion valve. This vapor decreases the capacity of the expansion valve very little as the valve opens to compensate for its presence. As the quantity of liquid in the condenser decreases, the operating pressure will drop there and throughout the high side of the system. As the refrigerant continues to be expelled, the pressure available to force the liquid through the expansion valve will continue to decrease, and, eventually, the valve's orifice will prove to be too much of a restriction for adequate flow, even with the needle fully withdrawn.
At this point, low side pressure will start to drop, and severe reduction in cooling capacity, marked by freeze-up of the evaporator coil, will result. Eventually, the operating pressure of the evaporator will be lower than the pressure of the atmosphere surrounding it, and air will be drawn into the system wherever there are leaks in the low side.
Because all atmospheric air contains at least some moisture, water will enter the system and mix with the refrigerant and oil. Trace amounts of moisture will cause sludging of the oil, and corrosion of the system. Saturation and clogging of the filter/drier, and freezing of the expansion valve orifice will eventually result. As air fills the system to a greater and greater extent, it will interfere more and more with the normal flows of refrigerant and heat.
From this description, it should be obvious that much of the technician's time will be spent detecting leaks, repairing them, and then restoring the purity and quantity of the refrigerant charge. A list of general rules should be followed in addition to all safety precautions:
Because of 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:
Some vehicles covered by this repair guide are equipped with R-134a, NOT R-12 refrigerant. These 2 refrigerants are NOT compatible. Using the incorrect refrigerant in an R-134a system will lead to compressor failure, refrigerant oil sludge and/or poor air conditioning system performance.
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. Ozone filters out harmful radiation from the sun.
Be sure to consult the laws in your area before servicing the air conditioning system. In some cases, it is illegal to perform repairs involving refrigerant unless the work is done by a certified technician.
Most repair work on an air conditioning system should be left to a certified professional. DO NOT, under any circumstances, attempt to loosen or tighten any fittings or perform any work other than that outlined here.
It is possible to detect possible air conditioning system problems by a visual inspection. Check for a broken air conditioning belt, dirt blocking the condenser, disconnected wires, a loose compressor clutch, and oily residue around the air conditioning hose fittings. Missing service gauge port caps may also cause a leak to develop.
REFRIGERANT LEVEL CHECKS
The only way to accurately check the refrigerant level is to measure the system evaporator pressures with a manifold gauge set, although rapid on/off cycling of the compressor clutch indicates that the air conditioning system is low on refrigerant. The normal refrigerant capacity is 39-41 oz. (1106-1162 grams).
The following procedure is for the attachment of a manifold gauge set to the service gauge port valves. If charging station equipment is used, follow the equipment manufacturer's instructions.
- Turn both manifold gauge set valves fully clockwise to close the high and low pressure hoses at the gauge set refrigerant center outlet.
Rotunda high side adapter set D81L-19703-A or Motorcraft Tool YT-354/355 (or equivalent) is required to connect the manifold gauge set or a charging station to the high pressure service access gauge port valve.
- Remove the caps from the high and low pressure service gauge port valves.
- If the manifold gauge set hoses do not have the valve depressing pins in them, install fitting adapters T71P-19703-S and R containing the pins on the manifold gauge hoses.
- Connect the high and low pressure refrigerant hoses to their respective service ports, making sure they are hooked up correctly and fully seated. Tighten the fittings by hand, making sure they are not cross-threaded. Remember that an adapter is necessary to connect the manifold gauge hose to the high pressure fitting.
DISCHARGING THE SYSTEM
Air conditioning system 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. Ozone filters out harmful radiation from the sun. ALWAYS use an approved recovery/recycling machine that meets SAE standards when discharging the air conditioning system. Follow the operating instructions provided with the approved equipment exactly to properly discharge the air conditioning system.
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 system or recycling station is used, the following general procedures should be followed, in addition to the operating instructions provided by the equipment manufacturer.
- Connect the refrigerant recycling station hose(s) to the vehicle air conditioning service ports and the recovery station inlet fitting.
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 to minimize the amount of refrigerant released when the hoses are disconnected.
- Turn the power to the recycling station ON to start the recovery process. Allow the recycling 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 the electrical system. On other units it may be necessary to manually turn off the pump.
- Once the recycling station has evacuated the vehicle air conditioning system, close the station inlet valve, if equipped. Then, switch OFF the electrical power.
- 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 recycling station hose(s).
- If the system pressure rises, repeat Steps 2, 3 and 4 until the vacuum level remains stable for 2 minutes.
EVACUATING THE SYSTEM
Some 1992 and later vehicles use R-134a refrigerant in place of the conventional R-12 refrigerant. Refer to the information on R-134a refrigerant systems in this Section. Also, any air conditioning equipment used to service R-12 refrigerant systems CANNOT be used to service R-134a refrigerant systems.
Connect a manifold gauge set as follows:
- Turn both manifold gauge set valves fully to the right, to close the high and low pressure hoses to the center manifold and hose.
- Remove the caps from the high and low pressure service gauge port valves.
- If the manifold gauge set hoses do not have valve depressing pins in them, install fitting adapters T71P19703S and R or equivalent, which have pins, on the low and high pressure hoses.
- Connect the high and low pressure hoses, or adapters, to the respective high and low pressure service gauge port valves. High side adapter set D81L-19703-A or tool YT-354/355 or equivalent is required to connect a manifold gauge set or charging station to the high pressure gauge port valve.Service tee fitting D87P-19703-A, which may be mounted on the clutch cycling pressure switch fitting, is available for use in the low pressure side of fixed orifice tube systems, to be used in place of the low pressure gauge port valve.
- Leak test all connections and components with flame-type leak detector 023-00006 or equivalent, or electronic leak detector 055-00014, 055-00015 or equivalent.
Good ventilation is necessary in the area where air conditioning leak testing is to be done. If the surrounding air is contaminated with refrigerant gas, the leak detector will indicate this gas all the time. Odors from other chemicals such as antifreeze, diesel fuel, disc brake cleaner or other cleaning solvents can cause the same problem. A fan, even in a well ventilated area, is very helpful in removing small traces of air contamination that might affect the leak detector.
- Using an approved recovery/recycling station, properly discharge the refrigerant system.
- Make sure both manifold gauge valves are turned fully clockwise. Make sure the center hose connection at the manifold gauge is tight.
- Connect the manifold gauge set center hose to a vacuum pump.
- Open the manifold gauge set valves and start the vacuum pump.
- Evacuate the system with the vacuum pump until the low pressure gauge reads at least 25 in. Hg (84 kPa) or as close to 30 in. Hg (101 kPa) as possible. Continue to operate the vacuum pump for 15 minutes. If a part of the system has been replaced, continue to operate the vacuum pump for another 20-30 minutes.
- When evacuation of the system is complete, close the manifold gauge set valves and turn the vacuum pump OFF .
- Observe the low pressure gauge for 5 minutes to ensure that system vacuum is held. If vacuum is held, charge the system. If vacuum is not held for 5 minutes, leak test the system, service the leaks and evacuate the system again.
CHARGING THE SYSTEM
Some 1992 and later vehicles use R-134a refrigerant in place of the conventional type R-12 refrigerant. Refer to the information on R-134a refrigerant systems in this section. Also any air conditioning equipment used to service R-12 refrigerant systems CANNOT be used to service R-134a refrigerant systems.
- Connect a manifold gauge set according to the proper procedure. Properly discharge and evacuate the system.
- With the manifold gauge set valves closed to the center hose, disconnect the vacuum pump from the manifold gauge set.
- Connect the center hose of the manifold gauge set to a refrigerant drum.
Use only a safety type dispensing valve.
- Loosen the center hose at the manifold gauge set and open the refrigerant drum valve. Purge air and moisture from the center hose, then tighten the center hose connection at the manifold gauge set.
- Detach the wire harness snap lock connector from the clutch cycling or low pressure switch and install a jumper wire across the 2 terminals of the connector.
- Open the manifold gauge set low side valve to allow refrigerant to enter the system. Keep the refrigerant container in an upright position.
- When no more refrigerant is being drawn into the system, start the engine and set the control assembly to the MAX cold and HI blower positions to draw the remaining refrigerant into the system. If equipped, press the air conditioning switch. Continue to add refrigerant to the system until the specified weight of the refrigerant is in the system. Then close the manifold gauge set low pressure valve and the refrigerant supply valve.
- Remove the jumper wire from the clutch cycling or low pressure switch snap lock connector. Attach the connector to the pressure switch.
- Operate the system until pressures stabilize to verify normal operation and system pressures.
- In high ambient temperatures, it may be necessary to operate a high volume fan positioned to blow air through the radiator and condenser to aid in cooling the engine and prevent excessive refrigerant system pressures.
- When charging is completed and system operating pressures are normal, disconnect the manifold gauge set from the vehicle. Install the protective caps on the service gauge port valves.
LEAK TESTING THE SYSTEM
Connect the manifold gauge set. Be sure that both valves are closed. Both gauges should read about 122-163 in. Hg (413-551 kPa) with the engine not running. If very little or no pressure is indicated, leave the vacuum pump valve closed. Open the refrigerant tank valve and set the low pressure gauge valve to the counterclockwise position. This will open the system to tank pressure. Check all system connections, the compressor head gasket and shaft seal for leaks using a leak detector tool.