There are two particular hazards associated with air conditioning systems and they both relate to the refrigerant gas.
First, the refrigerant gas is an extremely cold substance. When exposed to air, it win instantly freeze any surface it comes in contact with, including your eyes. The other hazard relates to fire. Although normally non-toxic, refrigerant gas becomes highly poisonous in the presence of an open flame. One good whiff of the vapor formed by burning refrigerant can be fatal. Keep all forms of fire (including cigarettes) well clear of the air conditioning system.
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 an automobile can easily cause a sufficient cracking or loosening of the air conditioning fittings. As a result, the extreme operating pressures of the system 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eventually, the valve's orifice will prove to be too much of a restriction for adequate flow even with the needle fully withdrawn.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 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 doing this 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.
- 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.
- Use only refrigerant 12. Purchase refrigerant intended for use in only automotive air conditioning system. Avoid the use of refrigerant 12 that may be packaged for another use 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 longer.
- 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.
Checking for Oil Leaks
Refrigerant leaks show up only 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 tube connections. If there are oily deposits, the system may have a leak, and you should have it checked by a certified technician.
A small area of oil on the front of the compressor is normal and no cause for alarm.Keep 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.Operate the System Periodically
A lot of air conditioning problems can be avoided by simply running the air conditioner at least once a week, regardless of the season. Simply let the system run for at least 5 minutes a week (even in the winter). This may seem absurd, but doing this keeps the internal parts lubricated as well as preventing the hoses from hardening.Checking the Air Conditioning Drive Belt
This belt receives the same kind of attention and inspection as the other drive belts. The only basic difference is that this belt is a heavy duty type and runs with more tension. Deflection should be measured at the center of the very long run between the compressor pulley and tensioner pulley.Antifreeze
In order to prevent heater core freeze-up during air conditioning 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 inhibition 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 pressure 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.
Acura recommends that the air conditioning system be serviced by using an approved refrigerant recovery/recycling machine.
DISCHARGING THE SYSTEM
See Figures 1, 2 and 3
- Connect an approved refrigerant recovery/recycling machine.
- Set the recovery system to its discharge position.
- After the gauge reading drops below 50 psi (434 kPa) slowly open the low pressure valve.
- As the system pressure drops, slowly open the high and low pressure valve until gauges read zero.
EVACUATING THE SYSTEM
This procedure requires the use of an approved refrigerant recycling/recovery machine.
- Connect the recovery station.
- Discharge the system.
- Operate the system until the vacuum gauge reading is about 700mm Hg, then slowly open the high pressure valve.
- When the gauge reading reaches 700 mm Hg, close any valves. If after 5-10 minutes, the gauge reading doesn't change, restart the pump and open the valves.
- Leak test the system. Close both gauge set valves. Turn off the pump and note the low side gauge reading. 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.
- Disconnect the system. The system is now ready for charging.
Leak test the air conditioning system whenever the system is suspect of losing it's 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 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 a 1/2 lb. charge in the system for a leak to be detected.
If a leak is found, perform the following:
- 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.
- Cheek the compressor oil and add more oil as required.
- 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 refrigerant recharging station to the system. Connect the high side first.
- Operate the charging station in charge mode.
- Run the engine at fast idle and turn the air conditioner to the maximum cooling mode. The compressor will operate and pull refrigerant gas into the system.
- When the charging process has been completed, run the system for at least five minutes to allow it to normalize.
- Disconnect the recovery station and install the dust caps on the service valves.