Because of the 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.
- 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 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 line wrenches when tightening these flare nut fittings.)
- Do not attempt to discharge the system by merely loosening a filter, or removing the service valve caps and opening these valves. Precise control is possible only when using a proper A/C refrigerant recovery station. Wear protective gloves when connecting or disconnecting service gauge hoses.
- Never start a system without first verifying that both service valves are properly installed, and that all fittings throughout the system are snugly connected.
- Avoid applying heat to any refrigerant line or storage vessel. Never allow a refrigerant storage container to sit out in the sun, or any other sources of heat, such as a radiator.
- 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.
- 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 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.
- 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.
- When servicing the system, minimize the time that any refrigerant line is open to the air, in order to prevent dirt and moisture entering the system. 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.
The air conditioning system should be checked periodically for worn hoses, loose connections, low refrigerant, leaks, dirt and bugs in the condenser. If any of these conditions exist, they must be corrected or they will reduce the efficiency of your air conditioning system.Checking the System for 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 technician.
Keeping the Condenser Clear
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 needle-nosed pliers. You can remove any debris with a stiff bristle brush or hose.Periodic System Operation
A lot of A/C problems can be avoided by simply running the air conditioner at least once a week, regardless of the season. Let the system run for at least 5 minutes a week (even in the winter), and you'll keep the internal parts lubricated as well as preventing the hoses from hardening.
Refrigerant Level Check
The first order of business is to find the sight glass. 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 found it, wipe it clean and proceed as follows:
- With the engine and the air conditioning system running, look for the flow of refrigerant through the sight glass. If the air conditioner is working properly, you'll be able to see a continuous flow of clear refrigerant through the sight glass, with perhaps an occasional bubble at very high temperatures.
- Cycle the air conditioner ON and OFF to make sure what you are seeing is clear refrigerant. Since the refrigerant is clear, it is possible to mistake a completely discharged system for one that is fully charged. Turn the system off and watch the sight glass. If there is refrigerant in the system, you'll see bubbles during the off cycle. If you observe no bubbles when the system is running, and the air flow from the unit in the vehicle is delivering cold air, everything is OK.
- If you observe bubbles in the sight glass while the system is operating, the system is low on refrigerant. Have it checked by a certified technician.
- 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.
Most of the service work performed in air conditioning requires the use of a set of two gauges, one for the high (discharge) 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 no less than 30 in. Hg (0-206 kPa) and the pressure graduations read from 0 to no less than 60 in. Hg (413 kPa).
The high side gauge measures pressure from 0 to at least 600 in. Hg (0-4137 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 perform the following services:
The manifold valves are designed so 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.
DISCHARGING THE 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 and recycling station is available, the following general procedures should be observed, in addition to the operating instructions provided by the equipment manufacturer.
- Check the system for pressure using the manifold gauge set. Take note, if a recovery system is used to draw refrigerant from the system that is already ruptured and open to the atmosphere, only air may be pulled into the tank.
- Connect the recycling station hoses to the vehicle's air conditioning service ports and the recovery stations inlet fitting.
- Turn the power to the recycling station ON to start the recovery process. Allow the 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 it's electrical system. On other units it may be necessary to turn off the pump manually.
- Once the recycling station has evacuated the system, close the station inlet valve. 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 station's hoses.
- If the system pressure rises, repeat Steps 3, 4 and 5 until the vacuum level remains stable for 2 minutes.
- If A/C oil is expelled during the discharge procedure, measure the amount discharged so the proper quantity of oil can be replaced when charging.
EVACUATING/CHARGING THE SYSTEM
Evacuating and charging the air conditioning system is a combined procedure in which the lines are purged, then refrigerant is added to the system in proper quantity. Charging is always conducted through the low pressure fitting. NEVER attempt to charge the air conditioner through the high pressure side of the system.
If a charging station and pump is available, the following general procedures should be observed, in addition to the operating instructions provided by the manufacturer.
- The proper amount of fresh compressor oil must be added to the system before charging. This can be accomplished by disconnecting the suction hose and pouring the fresh oil into the hose or pipe and then reconnecting the system.
- Properly connect a manifold gauge set to the vehicle, then connect the center manifold gauge hose to a vacuum pump.
- Turn the vacuum pump ON and slowly open the high and the low side valves to the pump. Allow the system to evacuate for 25-30 minutes, then note the gauge readings. If the system is unable to reach 28-29 in. Hg (193-199 kPa), of vacuum, the system and vacuum pump must be checked for leaks and repaired before proceeding further.
- After the system has been evacuated for at least 25 minutes, close the gauge high and low side valves then shut the pump OFF .
- Watch the low side gauge for vacuum loss. If vacuum loss is in excess of 1 in. Hg (3 kPa), then leak test the system, repair the leaks and return to Step 1. Before leak testing, remember to disconnect the gauge high side connector from the service port.
- If after 1-3 minutes, the loss is less than 1 in. Hg (3 kPa), then proceed with the system charging.
- Disconnect the gauge high side connection from the service port and the hose from the vacuum pump.
- Engage the center manifold connection to an R-12 source. If you are using a refrigerant drum instead of a charging station, place the drum on a scale to determine the amount of refrigerant being used.
- Open the source and the low side gauge valve, then monitor the weight of the drum or the rate at which the charging system is introducing the R-12 into the system.
- When 1 lb. (0.454 Kg) of R-12 has been added to the system, start the engine and turn the air conditioning system ON . Set the temperature level to full cold, the blower speed on high and the selector lever to the dash outlets. Under this condition, slowly draw in the remainder of the R-12 charge. The proper amount can be found on a label either on the compressor or on the evaporator case on the firewall.
- When the system is charged, turn the source valve OFF and continue to run the engine for 30 seconds in order to clear the gauges and the lines
- With the engine still running, carefully remove the gauge low side hose from the suction service fitting. Unscrew the connection rapidly to avoid excess refrigerant loss.
- Install the protective service fitting caps and hand-tighten.
- Turn the engine and air conditioning OFF .
- If an electronic or halide leak tester is available, test the system for leaks.
- If there are no leaks, perform the refrigerant level test to verify proper system charging.
Whenever a refrigerant leak is suspected, begin by checking for leaks at the fitting or valves. There are several methods of detecting leaks in the air conditioning system; among them the two most popular are (1) halide leak detection or the "open flame method", and (2) electronic leak-detection. Use of an electronic leak detector, if available, is preferable for ease and safety of operation.
The halide leak detector is a torch-like device which produces a yellow-green color when refrigerant is introduced into the flame at the burner. A purple or violet color indicates large amounts of refrigerant at the burner.
An electronic leak detector is a small portable electronic device with an extended probe. With the unit activated the probe is passed along those components of the system which contain refrigerant. If a leak is detected, the unit will sound an alarm signal or activate a display signal depending on the manufacturer's design. Follow the manufacturer's instructions carefully. Move the probe at approximately 1 in. (25mm) per second around the suspected leak area. When escaping refrigerant gas is located, the ticking or beeping signal from the detector will increase in beeps per second. If the gas is relatively concentrated, the signal will be a constant shrill.
If a tester is not available, perform a visual inspection and apply a soap and water solution to the questionable area or fitting. Bubbles will form to indicate a leak. Make sure to rinse the solution from the area before making repairs.