Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide

Air Conditioning System

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GENERAL SERVICING PROCEDURES



Operate the air conditioner for a few minutes, every month or so, during the cold months. This avoids the possibility of the compressor seals drying out from lack of lubrication.

To properly discharge and charge the A/C system a special charging system, quick connectors, complete training in refrigerant recycling and service procedures and a certification license is absolutely necessary. DO NOT VENT ANY AMOUNT (EVEN SMALL AMOUNTS-UNDER PENALTY OF LAW) OF REFRIGERANT INTO THE ATMOSPHERE.

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 in a truck can easily cause a sufficient cracking or loosening of the air conditioning fittings. As a result, the extreme operating pressures of the system forces 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, 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 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eventually, the valve's orifice will prove to be too much of a restriction for adequate flow even with the needle fully withdrawn.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 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.

Because all atmospheric air contains at least some moisture, water will enter the system and mix with the refrigerant and the 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 extend, it will interfere more and more with the normal flows of refrigerant and heat.

SERVICE PRECAUTIONS



A list of general precautions that should be observed while servicing the system include:



You must be certified to work on air conditioning systems in order to buy any refrigerant.
 
It is illegal to service an air conditioning system unless certified and trained to do so.
 
Keep all tools as clean and dry as possible.
 
Thoroughly purge the service gauges and hoses of air and moisture before connecting them to the system. Keep them capped when not in use.
 
Thoroughly clean any refrigerant fitting before disconnecting it, in order to minimize the entrance of dirt into the system.
 
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.
 
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.
 


WARNING
Use the correct refrigerant only. R-12 and R-134a must never be mixed, even in the smallest amounts. These two refrigerant systems are not compatible, mixing these will result in damage to your air conditioning system.



Completely evacuate any system that has been opened to replace a component, other than when isolating the compressor, 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 3 hours.



Use a wrench on both halves of a fitting that is to be disconnected, so as to avoid placing torque on any of the refrigerant lines.
 

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 (-9°C) or lower. A reading of -15°F (-26°C) 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 specified.

Radiator Cap

For efficient operation of an air conditioned truck's cooling system, the radiator cap should have a holding pressure which meets manufacturer's specifications. A cap which fails to hold this pressure 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 is normally a single molded drain tube which expels the condensation, that 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.

SAFETY PRECAUTIONS



Check with your local authorities before attempting to service you vehicle's A/C system. In most areas it is illegal to purchase R-12 or R-134a and service the system unless you are a certified technician.


CAUTION
The compressed refrigerant used in the air conditioning system expands into the atmosphere at a temperature of -21.7°F (-29.8°C) or lower. This will freeze any surface, including your eyes, that it contacts. In addition, R-12 refrigerant decomposes into a poisonous gas in the presence of a flame. Do not open or disconnect any part of the air conditioning system, near 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 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 refrigerant tubing. (It is advisable, when possible, to use tube or line wrenches when tightening these flare nut fittings.)
 
Never start a system without first verifying that both service valves are backseated, if equipped, and that all fittings are throughout the system are snugly connected.
 
Avoid applying heat to any refrigerant line or storage vessel. Charging may be aided by using water heated to less than +125°F (+51°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.
 
Always wear safety goggles when working on a system to protect the eyes. If refrigerant contacts the eyes, it is advisable in all cases to see a physician as soon as possible.
 
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.
 
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 truck
 
Always completely discharge and recover the system before painting the vehicle (if the paint is to be baked on), or before welding anywhere near the refrigerant lines.
 

TEST GAUGES



Most of the service work performed in air conditioning requires the use of a set of two gauges, one for the high (head) 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 0-30 in. Hg (0-101 kPa) and the pressure graduations read from 0 to no less than 60 psi (413 kPa).

The high side gauge measures pressure from 0 to at least 600 psi (4134 kPa).

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 test high and low side pressures.

The manifold valves are designed so that they have no direct effect on gauge readings, but serve only to provide for, or cut off, 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.

INSPECTION




CAUTION
The compressed refrigerant used in the air conditioning system expands into the atmosphere at a temperature of -21.7°F (-29.8°C) or lower. This will freeze any surface, including your eyes, that it contacts. In addition, the refrigerant decomposes into a poisonous gas in the presence of a flame. Do not open or disconnect any part of the air conditioning system.

Sight Glass Check

See Figures 1 and 2

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).

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

  1. Clean the sight glass, which is located on the top of the refrigerant receiver canister in the engine compartment.
  2.  
  3. Start the vehicle's engine.
  4.  
  5. Push the air conditioning button to operate the compressor, place the blower switch to HIGH, and move the temperature lever to the extreme left.
  6.  
  7. After operating for a few minutes in this manner, check the sight glass
    1. If the sight glass is clear, the magnetic clutch is engaged, the compressor discharge line is warm, and the compressor inlet line is cool, the system has a full charge.
    2.  
    3. If the sight glass is clear, the magnetic clutch is engaged, and there is no significant difference between the compressor inlet and the discharge lines, the system has most of its refrigerant charge.
    4.  
    5. If the sight glass is clear and the magnetic clutch is disengaged, the clutch is faulty or the system is out of refrigerant. Take the vehicle to a certified mechanic for servicing.
    6.  
    7. If the sight glass shows bubbles or foam, the system could be low on refrigerant or the receiver is restricted. Occasional foam or bubbles are normal when the ambient temperature is above 110°F (43°C) or below 70°F (21°C). Take the vehicle to a certified mechanic for servicing.
    8.  

  8.  



Click image to see an enlarged view

Fig. Fig. 1: Sight glass location-R-12 system



Click image to see an enlarged view

Fig. Fig. 2: Sight glass location-R-134a system


WARNING
If it is determined that the system has a leak, it should be corrected as soon as possible. Leaks may allow moisture or contaminants to enter and cause a very expensive problem.

DISCHARGING, EVACUATING AND CHARGING THE SYSTEM



To properly discharge and charge the A/C system a special charging system, quick connectors, complete training in refrigerant recycling/special service procedures, and a certification license is absolutely necessary. DO NOT VENT ANY AMOUNT (EVEN SMALL AMOUNTS-UNDER PENALTY OF LAW) OF REFRIGERANT INTO THE ATMOSPHERE.

If you are not properly trained and certified, take the vehicle to a certified mechanic in order to have the system evacuated and discharged. Immediately after finishing work on the vehicle, take the truck back to the mechanic to have the system recharged as soon as possible.

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!

 
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