See Figures 1, 2, 3 and 4
The purpose of the air conditioning system is to maintain a comfortable environment inside the passenger compartment by controlling air temperature, circulation, humidity and purity. The air conditioning system is designed to cycle a compressor on and off to maintain the desired cooling within the passenger compartment. Passenger compartment comfort is maintained by the temperature lever or switch located on the control head. The system is also designed to prevent the evaporator from freezing.
When an air conditioning mode is selected, electrical current is sent to the compressor clutch coil. The clutch plate and the hub assembly is then drawn rearward, which then engages the pulley. The clutch plate and pulley are then locked together and act as one unit. This, in turn, drives the compressor shaft, which compresses low pressure refrigerant vapor from the evaporator into high pressure. The compressor also circulates refrigerant oil and refrigerant through the air conditioner system. On certain models, the compressor is equipped with a cut-off solenoid which will shut the compressor off momentarily under certain conditions such as wide-open throttle and low idle speed.
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, 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 12 (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.
From the preceding description, it should be obvious that much of a repairman's time will be spent detecting leaks, repairing them, and restoring the purity and quantity of the refrigerant charge.
When working with air conditioning systems and R-12 refrigerant, be EXTREMELY careful to observe the following safety precautions:
- 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 excessive torsional stress on refrigerant tubing. (It is advisable, when possible, to use tube or line wrenches when tightening these flare nut fittings).
- Do not attempt to discharge the system by merely loosening a fitting, or removing the service valve caps and cracking these valves. Discharging an A/C system without an approved R-12 recovery/recycling station may be illegal in your area, and precise control is possibly only when using the service gauges. Wear protective gloves when connecting or disconnecting service gauge hoses. Escaping refrigerant will immediately freeze any part of the body that it comes in contact with (frostbite). If frostbite does occur, consult a physician immediately.
- Discharge the system only in a well ventilated area, as high concentrations of the gas can exclude oxygen and act as an anesthesia. When leak testing or soldering, this is particularly important, as toxic phosgene gas is formed when R-12 contacts any flame. Phosgene gas is fatal to both humans and animals. Never smoke near R-12 or allow it to discharge into an open flame.
- Never start a system without first verifying that both service valves (if so equipped) are backseated, and that all fittings 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 goggles when working on a system to protect the eyes. If refrigerant contacts the eye, see a physician as soon as possible. Goggles are an inexpensive insurance policy that could save your sight.
- 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 car.
- 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.
GENERAL SERVICING PROCEDURES
In addition to the preceding safety precautions, the following list of general procedures should be observed while servicing an air conditioning system:
- 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 R-12 refrigerant.
Although you are unlikely to find R-12 for sale to the general public, DO NOT use old containers of impure R-12 which were intended to power air horns or other devices.
- 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).
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 the most important check of an air conditioning system is a visual inspection of the system's components. Periodically inspect the air conditioning system for refrigerant leaks, damaged compressor clutch, unsatisfactory compressor drive belt tension/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 surface of the radiator and condenser for dirt, leaves or other material which might block air flow.
- Check for kinks in hoses and lines. Check the system for leaks.
- Make sure the drive belt is under the proper tension. When the compressor is operating, make sure the drive belt is free of noise or slippage.
- Make sure the blower motor operates at all appropriate positions, then check for air distribution from all outlets with the blower on HIGH .
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.
- Make sure the air passage selection lever or switch is operating correctly. Start the engine and warm it to normal operating temperature, then make sure the hot/cold selector is operating correctly.
- Connect the manifold gauge set to the high and low pressure fittings, as described later in this section.
- Run the engine at fast idle (about 1,500 rpm) and turn the air conditioner onto its maximum setting.
Check the compressor for the following:
- Normal high and low pressure
- Metallic sound from the compressor (replace the compressor)
- Oil leaks. Refrigerant leaks show up as oily areas on the various components because the compressor oil is transported around the entire system along with the refrigerant. Look for oily spots on all the hoses and lines, and especially on the hose and tubing connections. If there are oily deposits, the system may have a leak, and you should have it checked by a qualified repairman.
- Repair or replace the compressor as necessary.
Check the magnetic clutch for the following:
- Oil leaks from the pressure plate and pulley
- Noise or leakage from the clutch bearings
- Turn the air conditioner off and stop the engine.
- Make sure that the high and low pressure readings on the gauges are the same immediately after the unit is shut off. If they are not the same, this suggests that the gasket or the valve inside the compressor is damaged.
- Using an ohmmeter, check the resistance of the stator coil between the clutch lead wire and ground. The standard resistance at 68°F (20°C) is 2.7-3.1 ohms. If the resistance is not within specification, replace the magnetic coil.
- Periodically inspect the front of the condenser for bent fins or foreign material (dirt, bugs, leaves, etc.) If any cooling fins are bent, straighten them carefully with needlenose pliers. You can remove any debris with a stiff bristle brush or hose.
- Check the condenser fittings for leakage, and tighten them as necessary.
Bug screens are regarded as obstructions and should be avoided, if possible.Condenser Fan
Connect terminal B of the fan motor to ground to make sure that the motor operates.Receiver/Drier
- Using a leak detector, inspect the sight glass, fuse plugs and refrigerant fittings for leakage.
Check the receiver/drier for clogging as follows:
- Run the engine at fast idle with the air conditioner on.
- Feel the inlet and outlet piping with your hand. If there is a great difference in temperature, replace the receiver/drier.
- Connect the manifold gauge set to the high and low pressure fittings as described in this section.
- Run the engine at fast idle (about 1500 rpm) and turn the air conditioner on and set it to MAX COOLING.
- Check the high and low pressures. The high pressure should be between 210-260 psi (1,448-1,793 kPa). The low pressure should be between 28-43 psi (193-296 kPa).
- If the low pressure is below the limit, replace the expansion valve. If the low pressure is too high, tighten the sensing bulb well located on the evaporator case. If that does not correct the problem, replace the expansion valve.
- Using a leak detector, check all the fittings for leaks. Replace O-rings or the line as necessary.
- Check all the hose and pipe clamps for looseness and tighten as necessary.
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.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.
Many air conditioning problems can be avoided by simply running the air conditioner periodically, regardless of the season. Simply let the system run for a few minutes every week or so, even in the winter. This will help keep internal parts, such as the compressor seals and O-rings, lubricated, as well as prevent hoses from hardening.
REFRIGERANT LEVEL CHECK
The appropriate way to check refrigerant level depends on the design of your vehicle's air conditioning system. Generally, when a system is equipped with a sight glass, the sight glass is used to evaluate charge condition. On vehicles not so equipped, the charge condition can be determined by comparing temperatures of various system lines.With Sight Glass
See Figures 5, 6 and 7
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.
The first order of business when checking the sight glass is to locate it. It will either be in the head of the receiver/drier, or in one of the metal lines leading from the top of the receiver/drier. Once you've located the sight glass, wipe it clean and proceed as follows:
- 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.
Observe the sight glass:
- If you see bubbles, the system is low on refrigerant and must be recharged. Very likely there is a leak at some point.
- Oil streaks in the sight glass are an indication of trouble. Most of the time, if you see oil in the sight glass, it will appear as a series of streaks, although occasionally it may be a solid stream of oil. In either case, it means that part of the charge has been lost.
- 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.
On vehicles without a sight glass, the receiver/drier is known as a receiver-drier/accumulator and is connected to the system differently. On a standard system containing a sight glass, the drier is in a high pressure line running from the bottom of the condenser (in front of the radiator) to the expansion valve (a small part shaped somewhat like a mushroom and mounted on or near the evaporator). On vehicles without a sight glass, however, the accumulator is located in a low pressure, large diameter line running from the evaporator to the suction side of the compressor.
Run the air conditioning unit with the vehicle windows open and the fan on high. Feel the temperature of the line going into the evaporator right at the evaporator unit itself, after the orifice tube fitting (where the line should go from warm to cold). Also feel the temperature of the line leaving the evaporator at the top and going into the accumulator. Feel the lower surface of the accumulator.
If the system has enough refrigerant, all these pipes should be at the same temperature. If it is low on refrigerant, the lower accumulator surface and line coming out of the evaporator will be warmer than the line going to the evaporator. If the line to the accumulator is cold but the accumulator surface is much warmer, the system may be just slightly undercharged.
If the line leading out of the accumulator and to the compressor is just as cold as the line going in, the system has excessive refrigerant in it. In case of either too little or too much refrigerant, have a professional refrigeration mechanic add or remove refrigerant as necessary.
MANIFOLD GAUGE SET
See Figure 8
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:
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.
The high and low pressure service valves are located on the high and low pressure refrigerant pipes.
- Close both valves of the manifold gauge set and connect the charging hoses to the manifold.
- Wipe the dirt and grease from the service fitting caps, then remove them.
- Connect the low pressure hose to the low pressure line fitting.
- Connect the high pressure hose to the high pressure line fitting.
Tighten the hose fittings by hand only.
- Suspend the manifold set from the hood latch or other convenient location.
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.
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, as described earlier in this section.
- Discharge the system, as described earlier in this section.
- 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.
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. The sight glass should be free of bubbles.
- 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.