The most important aspect of air conditioning service is the maintenance of a pure and adequate charge of refrigerant in the system. A refrigerant leak may occur because of a loose fitting or cracked line, caused by the vibrations commonly present on an engine during operation. A refrigeration system cannot function properly if a significant percentage of the charge is lost.
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eventually, the valve's orifice will prove to be too much of a restriction for adequate flow even with the needle fully withdrawn.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 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 R-12 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 extent, it will interfere more and more with the normal flows of refrigerant and heat.
A list of general precautions that should be observed while servicing an air conditioning system follows:
- 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.
- 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.
- Thoroughly clean any refrigerant fitting before disconnecting it, in order to minimize the entrance of dirt into the system.
- 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.
- 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.
- Use only Refrigerant 12. Purchase refrigerant intended only for use in automotive air conditioning systems. Avoid the use of Refrigerant 12 that may be packaged for another use, such as cleaning, or powering a horn, as it is impure.
- 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 12 hours (overnight). 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 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 the refrigerant tubing. (It is advisable, when possible, to use tube or line wrenches when tightening these flare nut fittings.)
- Always wear goggles when working on a system to protect the eyes. If refrigerant contacts the eye, it is advisable in all cases to see a physician as soon as possible.
- Wear protective gloves when connecting or disconnecting service gauge hoses.
- Avoid inhaling refrigerant, as high concentrations of the gas can exclude oxygen and act as an anesthetic.
- A toxic gas is formed when R-12 contacts any flame. Avoid refrigerant exposure to open flames when servicing any air conditioning system.
- Always keep refrigerant container fittings capped when not in use. Avoid sudden shock to the container which might occur from dropping it, or from banging a heavy tool against it. Never carry a refrigerant container in the passenger compartment of a car.
- Avoid applying heat to any refrigerant line or storage vessel. Charging may be aided by using water heated to less than 125°F (52°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 completely discharge the system using proper equipment before painting the vehicle (if the paint is to be baked on), or before welding anywhere near the refrigerant lines.
- If accidentally allowed to escape, compressed refrigerant could cause frostbite. 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.
- Never start a system without first verifying that both service valves, if equipped, are backseated and that all fittings throughout the system are snugly connected.
Check For Oil Leaks
Refrigerant leaks can sometimes appear as oily areas on various components due to the compressor oil that is transported along with refrigerant, throughout the air conditioning system. During your visual inspection of system components, look for oily spots on all air conditioning hoses and lines, especially in areas of hose and tube connections and crimpings. If oily deposits are present, the system may have a refrigerant leak at that point.Keep The Condenser Clear
Periodically inspect the front of the condenser for bent fins or foreign material (dirt, leaves, twigs, paper, etc.). If any cooling fins are bent, straighten the fins carefully using needle nose pliers. Remove any debris that may restrict air flow over the condenser. Reduced air flow over the condenser will decrease the efficiency of the air conditioning system.
Since they interfere with air flow over the condenser, bug screens are considered 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.
ADDITIONAL PREVENTIVE MAINTENANCE CHECKS
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.
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 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 condition.
REFRIGERANT LEVEL CHECKS
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 (21.1°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 system checks.
- Place the automatic transmission in Park or the manual transmission in Neutral. Set the parking brake.
- Run the engine at a fast idle (about 1,500 rpm) either with the help of a friend or by temporarily readjusting the idle speed screw.
- Set the controls for maximum cold with the blower on High.
- Locate the sight glass in one of the system lines. Usually it is on the left alongside the top of the radiator.
- If you see bubbles, the system must be recharged. Very likely there is a leak at some point.
- 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.
- 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 to the next step.
- Have an assistant in the car turn the fan control on and off to operate the compressor clutch. Watch the sight glass.
- 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.
Operate the air conditioner for a few minutes, every two weeks or so, during colder months. This avoids the possibility of the compressor seals drying out from lack of lubrication.
See Figure 3
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 to 30 inches 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 and the use of an approved R-12 recovery/recycling station 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 that they have no direct effect on 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 discharge, evacuate and charge the system. DISCHARGING THE 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. An approved R-12 recovery/recycling station that meets SAE standards should be used when discharging the system. Follow the operating instructions provided with the equipment exactly to properly discharge the system.
- Remove the caps from the high and low pressure charging valves in the high and low pressure lines.
- Connect an approved R-12 recovery/recycling station to the valves and follow the instructions provided with the unit.
- Open the low pressure gauge valve slightly and allow the system pressure to bleed off.
- When the system is just about empty, open the high pressure valve very slowly to avoid losing an excessive amount of refrigerant oil. Do not allow any refrigerant to escape.
EVACUATING THE SYSTEM
This procedure requires the use of a vacuum pump.
Before charging the air conditioning system, it is necessary to remove any trapped air and moisture with a vacuum pump. Failure to do so may result in poor operation of the system and possible component failure.
When evacuating an R-12 filled air conditioning system, an approved R-12 recovery/recycling station that meets SAE standards should be employed. Follow the operating instructions provided with the equipment exactly to properly discharge the system.
- Connect the manifold gauge set.
- Discharge the system.
- On 1983 and later models, make sure that the low pressure gauge set hose is connected to the low pressure service gauge port on the top center of the accumulator/drier assembly and the high pressure hose connected to the high pressure service gauge port on the compressor discharge line.
- Connect the center service hose to the inlet fitting of the vacuum pump.
- Turn both gauge set valves to the wide open position.
- Start the pump and note the low side gauge reading.
- Operate the pump until the low pressure gauge reads 25-30 in. Hg. Continue running the vacuum pump for 10 minutes more. If you have replaced some component in the system, run the pump for an additional 20-30 minutes.
- Leak test the system. Close both gauge set valves. Turn off the pump. The needle should remain stationary at the point at which the pump was turned off. If the needle drops to zero rapidly, there is a leak in the system which must be repaired.
Leak test the air conditioning system whenever the system is suspected of losing its charge, after component replacement or after any refrigerant lines have been disconnected. There are two generally accepted methods of checking the air conditioning system for leaks. One is with the use of a Halide torch and the other is with an electronic leak detector. Both are designed to detect small amounts of halogen when placed near a fitting or connection suspected of leaking. The electronic leak detector provides a greater degree of sensitivity and is the most preferred (and expensive) method. When using this equipment, make sure that you follow the manufacturer's instructions carefully.
Some leak tests can be performed with a soapy water solution, but there must be at least a1/2lb. charge in the system for a leak to be detected.
To leak test with soapy water, apply a water and soap solution to the air conditioning system fittings in the engine compartment and check for bubbles. The presence of bubbles indicates a leak.
Refrigerant leaks can sometimes appear as oily areas on various components, due to the compressor oil that is transported along with refrigerant, throughout the air conditioning system. During your visual inspection of system components, look for oily spots on all air conditioning hoses and lines, especially in areas of hose and tube connections and crimpings. If oily deposits are present, you may have a refrigerant leak at that point.
A slight amount of oil in front of the compressor may be normal. Unless the compressor or other system component is replaced, it is generally unnecessary to add refrigerant oil.
If a leak is found, have the system professionally repaired, or proceed as follows:
- Check the tightness of the suspect fitting or connection, and if necessary re-tighten it. Recheck for leaks with a leak detector.
- If leakage persists after re-tightening the fitting, discharge the refrigerant from the system and disconnect the fitting. Visually inspect the fitting seating surfaces for damage and replace as necessary. Even minor damage will require replacement of the fitting. If you disconnect a fitting for any reason, always replace the 0-ring.
- Partially charge the system and perform another leak test. If no leaks are found, discharge, evacuate and recharge the system.
CHARGING THE SYSTEM
- Connect an approved R-12 Recovery/Recycling station to the valves and follow the instructions provided with the unit.
- Open the R-12 source valve and allow liquid R-12 to flow into the system through the low side fitting.
- Turn on the A/C system and allow the compressor operation to draw in the remainder of the preset amount of R-12 into the system.
- Turn off the source valve and run the engine for 30 seconds to clear the lines and gauges.
- Quickly unscrew the adaptors and recap the fittings.
- Leak check the system and check for proper performance.
- When the charging process has been completed, close all valves. Run the system for at least five minutes to allow it to normalize. The low pressure side reading should be 4-25 psi; the high pressure reading should be 120-210 psi at an ambient temperature of 70-90°F (21-32°C).
The maximum charge for your vehicle's system is as follows:
- Connect an approved R-12 Recovery/Recycling station to the valves and follow the instructions provided with the unit.
- Disconnect the wire harness snap-lock connector from the clutch cycling pressure switch and install a jumper wire across the two terminals of the connector.
- Allow refrigerant to be drawn into the system.
- When no more refrigerant is drawn into the system, start the engine and run it at about 1,500 rpm. Turn on the system and operate it at the full high position. The compressor will operate and pull refrigerant gas into the system.
- When the charging process has been completed, close the gauge set valves and remove the jumper wire. Reattach the cycling clutch wire connector.
- Run the system for at least five minutes to allow it to normalize. The low pressure side reading should be 4-25 psi; the high pressure reading should be 120-210 psi at an ambient temperature of 70-90°F (21-32°C).
The maximum charge for your vehicle's system is 2 1 / 2 lbs.