Chrysler Full-Size Trucks 1967-1988 Repair Guide

Air Conditioning

Print

SAFETY PRECAUTIONS



See Figures 1 and 2


CAUTION
Because of the inherent dangers involved with working on air conditioning systems and R-12 refrigerant, NO-ONE should attempt to service their system unless they have the proper training and certification as well access to the necessary tools. When servicing an air conditioning system, all safety precautions must be strictly followed.

  1. 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.
  2.  
  3. 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 refrigerant tubing. (It is advisable, when possible, to use tube or line wrenches when tightening these flare nut fittings.)
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Basic air conditioning system components and flow diagram



Click image to see an enlarged view

Fig. Fig. 2: Schrader valve

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.

  1. Do not attempt to discharge the system by merely loosening a fitting, or removing the service valve caps and cracking these valves. Precise control is possible only when using the service gauges and a proper A/C refrigerant recovery station. Wear protective gloves when connecting or disconnecting service gauge hoses.
  2.  

Be sure to consult the laws in your area before servicing the air conditioning system. In many areas, it is illegal to perform repairs involving refrigerant unless the work is performed by a certified technician. Also, laws often restrict the sale of R-12 refrigerant only to people with proper certification.

  1. Work on the system only in a well ventilated area, should high concentrations of the gas accidentally escape it could exclude oxygen and act as an anesthetic. When leak testing or soldering, this is particularly important, as toxic gas is formed when R-12 contacts any flame.
  2.  
  3. Never start a system without first verifying that both service valves are properly installed, and that all fittings throughout the system are snugly connected.
  4.  
  5. Avoid applying heat to any refrigerant line or storage vessel. Charging may be aided by using water heated to less than 125°F (50°C) to warm the refrigerant container. Never allow a refrigerant storage container to sit out in the sun, or near any other source of heat, such as a radiator.
  6.  
  7. Always wear goggles to protect your eyes when working on a system. If refrigerant contacts the eyes, it is advisable in all cases to see a physician as soon as possible.
  8.  
  9. Frostbite from liquid refrigerant should be treated by first gradually warming the area with cool water, and then gently applying petroleum jelly. A physician should be consulted.
  10.  
  11. Always keep refrigerant drum fittings capped when not in use. If the container is equipped with a safety cap to protect the valve, make sure the cap is in place when the can is not being used. Avoid sudden shock to the drum, which might occur from dropping it, or from banging a heavy tool against it. Never carry a drum in the passenger compartment of a car.
  12.  
  13. Always completely discharge the system into a suitable recovery unit before painting the vehicle (if the paint is to be baked on), or before welding anywhere near refrigerant lines.
  14.  
  15. When servicing the system, minimize the time that any refrigerant line or fitting is open to the air in order to prevent moisture or dirt from entering the system. Contaminants such as moisture or dirt can damage internal system components. Always replace O-rings on lines or fittings which are disconnected. Prior to installation coat, but do not soak, replacement O-rings with suitable compressor oil.
  16.  

GENERAL SERVICING PROCEDURES



See Figure 3

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 cracking or loosening of the air conditioning fittings; allowing, the extreme operating pressures of the system to 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 of refrigerant, and so a loss will first appear there 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 R-12 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 a 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.



Click image to see an enlarged view

Fig. Fig. 3: Common manifold gauge set

Because all atmospheric air contains at least some moisture, water will enter the system mixing with the R-12 and the oil. Trace amounts of moisture will cause slugging 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 how essential it is to find leaks, repair them, and then restore the purity and quantity of the refrigerant charge. A list of general rules should be followed in addition to all safety precautions:

  1. Keep all tools as clean and dry as possible.
  2.  
  3. Thoroughly purge the service gauges and hoses of air and moisture before connecting them to the system. Keep them capped when not in use.
  4.  
  5. Thoroughly clean any refrigerant fitting before disconnecting it, in order to minimize the entrance of dirt into the system.
  6.  
  7. 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.
  8.  
  9. When adding oil, pour it 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.
  10.  
  11. Use only R-12 refrigerant. Purchase refrigerant intended for use only in automatic air conditioning systems.
  12.  
  13. Completely evacuate any system that has been opened to replace a component, 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. If a system has been open for a considerable length of time it may be advisable to evacuate the system for up to 12 hours (overnight).
  14.  
  15. Whenever possible, use a wrench on both halves of a fitting that is to be connected/disconnected, so as to avoid placing torque on any of the refrigerant lines.
  16.  
  17. When overhauling a compressor, pour some of the oil into a clean glass and inspect it. If there is evidence of dirt or metal particles, or both, flush all refrigerant components with clean refrigerant before evacuating and recharging the system. In addition, if metal particles are present, the compressor should be replaced.
  18.  
  19. Schrader valves may leak only when under full operating pressure. Therefore, if leakage is suspected but cannot be located, operate the system with a full charge of refrigerant and look for leaks from all Schrader valves. Replace any faulty valves.
  20.  

Additional Preventive Maintenance Checks
ANTIFREEZE

In order to prevent heater core freeze-up during A/C operation, it is necessary to maintain permanent type antifreeze protection of +15°F, or lower. A reading of -15°F is ideal since this protection also supplies sufficient corrosion inhibitors for the protection of the engine cooling system.

The same antifreeze should not be used longer than the manufacturer specifies.

RADIATOR CAP

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

CONDENSER

Any obstruction of or damage to the condenser 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

This single molded drain tube expels the condensation, which accumulates on the bottom of the evaporator housing, into the engine compartment. If this tube is obstructed, the air conditioning performance can be restricted and condensation buildup can spill over onto the vehicle's floor.

SYSTEM INSPECTION



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.

The easiest and often most important check for the air conditioning system consists of a visual inspection of the system components. Visually inspect the air conditioning system for refrigerant leaks, damaged compressor clutch, compressor drive belt tension and condition, plugged evaporator drain tube, blocked condenser fins, disconnected or broken wires, blown fuses, corroded connections and poor insulation.

A refrigerant leak will usually appear as an oily residue at the leakage point in the system. The oily residue soon picks up dust or dirt particles from the surrounding air and appears greasy. Through time, this will build up and appear to be a heavy dirt impregnated grease. Most leaks are caused by damaged or missing O-ring seals at the component connections, damaged charging valve cores or missing service gauge port caps.

For a thorough visual and operational inspection, check the following:

  1. Check the surface of the radiator and condenser for dirt, leaves or other material which might block air flow.
  2.  
  3. Check for kinks in hoses and lines. Check the system for leaks.
  4.  
  5. Make sure the drive belt is under the proper tension. When the air conditioning is operating, make sure the drive belt is free of noise or slippage.
  6.  
  7. Make sure the blower motor operates at all appropriate positions, then check for distribution of the air from all outlets with the blower on HIGH.
  8.  

Keep in mind that under conditions of high humidity, air discharged from the A/C vents may not feel as cold as expected, even if the system is working properly. This is because the vaporized moisture in humid air retains heat more effectively than does dry air, making the humid air more difficult to cool.

  1. Start the engine and warm it to normal operating temperature, then make sure the hot/cold selection lever is operating correctly.
  2.  

SIGHT GLASS CHECK



See Figure 4

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 (21.1°C)).



Click image to see an enlarged view

Fig. Fig. 4: Sight glass inspection

If your vehicle is equipped with an aftermarket air conditioner, the following system check may not apply. You should contact the manufacture of the unit for instructions on systems check.

  1. Place the automatic transmission in Park or the manual transmission in Neutral. Set the parking brake.
  2.  
  3. Run the engine at fast idle (about 1,500 rpm) either with the help of a friend or by temporarily readjusting the idle speed screw.
  4.  
  5. Set the controls for maximum cold with the blower on High.
  6.  
  7. Locate the sight glass in one of the system lines. Usually it is on the left alongside the top of the radiator.
  8.  
  9. If you see bubbles, the system must be recharged. it is very likely then, that there is a leak at some point.
  10.  
  11. If there are no bubbles, there is either no refrigerant at all or the system is fully charged. Feel the two hoses going to the belt driven compressor. If they are both at the same temperature, the system is empty and must be recharged.
  12.  
  13. If one hose (high pressure) is warm and the other (low pressure) is cold, the system may be all right. However, you are probably making these tests because you think there is something wrong, so proceed with the next step.
  14.  
  15. Have an assistant turn the fan control on and off to operate the compressor clutch. Watch the sight glass.
  16.  
  17. If bubbles appear when the clutch is disengaged, the system is properly charged.
  18.  
  19. If the refrigerant takes more than 45 seconds the bubble when the clutch is disengaged, the system is overcharged. This usually causes poor cooling at low speeds.
  20.  


WARNING
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 a very expensive rust problem. Exercise the air conditioner for a few minutes, every two weeks or so, during the cold months. This avoids the possibility of the compressor seals drying out from lack of lubrication.

TESTING THE SYSTEM



See Figure 5

  1. Connect a gauge set.
  2.  
  3. Close (clockwise) both gauge set valves.
  4.  
  5. Park the truck in the shade at least 5 feet from any walls. Start the engine, set the parking brake, place the transmission in NEUTRAL and establish an idle of 1,100-1,300 rpm.
  6.  
  7. Run the air conditioning system for full cooling, in the MAX or COLD mode.
  8.  
  9. The low pressure gauge should read 5-20 psi: the high pressure gauge should indicate 12-180 psi.
  10.  



Click image to see an enlarged view

Fig. Fig. 5: Manual service valve positions

These pressures are the norm for an ambient the temperature of 70-80°F (21-27°C). Higher air temperatures along with high humidity will cause higher system pressures. At idle speed and an ambient temperature of 110°F (43°C), the high pressure reading can exceed 300 psi. Under these extreme conditions, you can keep the pressure down by directing a large electric floor fan through the condenser.

LEAK TESTING



Some leak tests can be performed with a soapy water solution. There must be at least a 1 / 2 lb. charge in the system for a leak to be detected. The most extensive leak tests are performed with either a Halide flame type leak tester or the more preferable electronic leak tester.

In either case, the equipment is expensive, and, the use of a Halide detector can be extremely hazardous!

DISCHARGING, EVACUATING AND CHARGING



Discharging, evacuating and charging the air conditioning system must be performed by a properly trained and certified mechanic in a facility equipped with refrigerant recovery/recycling equipment that meets SAE standards.

If a recovery station is available, carefully follow the tool manufacturer's instructions to assure safety and an prevent environmental pollution. If the system is discharged in order to service system components, be sure to cap ALL openings while lines are disconnected to prevent system contamination. Plan all service well ahead of time to minimize the amount of time the system must spend in a discharged state.

 
label.common.footer.alt.autozoneLogo