Since this becomes a recurring post during the summer months, I
thought I'd put together an FAQ type post to help explain just how an
air conditioning system works, what problems can arise with them, and
how they can be fixed.
Part I - The Air Conditioning System's Components
Most automotive air conditioning systems are made up of the same
components. By knowing what they are and how they work, you may be
able to save yourself a little time troubleshooting, or a few dollars
on a repair bill if you know what's going on ahead of time.
Freon: Freon is the refrigerant used in air conditioning systems. It's
purpose is to circulate through the system, transferring heat absorbed
by the evaporator (see below) and discharging that heat through the
condenser (see below).
For automotive usage, two types of freon have been used, designated
R-12 and R134a. R12 was the industry standard up until the years in
and between 1994 through 1996. Between these years, automakers were
told they had to switch from R-12 to R-134a, due to environmental
purposes. If your car is newer than 1996, it is 100% sure to be R134a.
If it is older than 1994, it is 99.9% sure to be R12. It is possible
to convert an R12 system to an R134a system, which will be discussed
Compressor: The compressor is the heart of the air conditioning
system. It's purpose is to pressurize and circulate the freon. The
compressor is made up of two parts: the compressor body and the
The compressor body is the non-servicible rear portion that actually
does the compressing.
The front portion, which the drive belt runs on, is multiple pieces
and can be serviced individually if desired. The clutch portion is
responsible for engaging the compressor on and off. Contrary to
popular belief, the a/c compressor is not working 100% of the time the
belt is spinning, only whenever this clutch is engaged. The coil is
the electrical portion which determines when the clutch will engage
and disengage. The hub is the portion which the belt runs on, and the
bearing allows the assembly to freely rotate.
Condenser: The condenser is the large coiled assembly located in front
of your vehicle's radiator. It's function is similar to that of a
radiator as well. It removes the heat from the refrigerant, changing
it from a hot vapor to a warm liquid.
Evaporator: The evaporator core is the non-visible part of your air
conditioning system. It is located inside your passenger compartment,
usually in close proxemity to your heater core, and removes the heat
and humidity from the passenger compartment.
Expansion Valve - or - Oriface Tube: The expansion valve or oriface tube's job is to regulate pressures throughout the system. An air conditioning system will have one or the other. If it has an oriface tube as opposed to an expansion valve, the oriface tube acts as an additional system filter as well.
Accumulator - or - Reciever Drier: The accumulator's job is to remove moisture from the air conditioning system, and to also allow any sediments or contaminents to settle out. This item is the circular canister that is visible in the engine compartment.
Part II - Troubleshooting the Air Conditioning System
Now comes the part you all are probably wanting, what to do, check and have replaced or repaired if your air conditioning system stops cooling properly.
Step One: The first step is to make sure the system is full of freon. There are one or two pressure switches built into the air conditioning lines that will not allow the compressor to operate if system pressures get too high (caused by obstruction) or too low (low freon amounts).
The first step in examining freon levels is to have SOMEONE that has a set of professional air conditioning pressure gauges examine the current system's pressure. This is why I usually do not recommend one of the "fill it yourself" kits available from most retail stores. The reason is, these kits only include one pressure gauge, and a proper air conditioning diagnosis cannot be done without examining both the suction and discharge sides' pressures.
Once the pressures are determined, if the system is low on freon, recharge it. If the system is the older (R12) style of freon, it is recommended to retrofit it to use R134a freon, as R12 freon is quite costly compared to R134a. The retrofit procedure is done by <b>completely</b> evacuating the system of R12, replacing the service port fittings, and recharging the system with R134a. The use of an evacuation/recharge-machine-safe UV dye is recommended.
Once the system is recharged, check the system for leaks. This can be done with either a freon "sniffer", or with a black light if a UV dye has been added to the system.
If all the system needed was a recharge, and no obvious leaks are detected, the system should be operable. A recharge every now and then is considered normal, as a small amout of freon does start to seep out with age, as the various seals, gaskets and o-rings throughout the system begin to get brittle and lose their sealing ability. If you are needing to recharge the system as frequently as every other year, there is a leak that needs to be repaired.
If you recharge the system and the pressures on both gauges read in their normal levels, yet the system is still not cooling, the first thing to check is for proper compressor operation.
Usually, the compressor clutch is operated by a relay. Test to make sure that the compressor clutch is getting the correct voltages at the correct times. If not, there is an electrical problem that will have to be tracked down. If the voltages are ok, check to see if the clutch is either burned up or locked up. If this is the case, the recommended procedure is to buy a new or remanufactured clutch, coil, hub and bearing assembly, as it is wise to replace these as a set, for prevention's sake.
NOTE: Before any system componants are replaced, the system must be fully discharged of any refrigerant.
If the clutch is switching on and off correctly and is physically able to operate, check to make sure the compressor itself is not locked. Usually if the a/c drive belt was thrown off, this has already happened. If this has happened, the compressor will need to be replaced. If a compressor replacement must be done, it is wise to replace the accumulator, and if applicable, the oriface tube, as these act as system filters, and will not allow system contaminants to reach the new compressor. A parts store or repair shop will usually not warranty a compressor unless there is proof that the accumulator and oriface have been changed also. Compressors are available with or without a clutch assembly; I personally recommend buying only those compressors with a new clutch, once again, for prevention's sake.
If there is any other componant leaking, it must be replaced, or if absolutely neccesary, repaired.
One last situation is that the system is full to capacity, the compressor clutch is operating as it should, and the compressor is functional, but either the suction or discharge side pressures are not correct. This is usually the sign of a blockage somewhere within the system. It is advisable to replace the oriface tube if equipped, or to first replace the expansion valve, if equipped. If these items have been replaced once, and either the oriface tube becomes plugged again, the expansion valve becomes inoperable again, or the gauges still show incorrect pressures, this is either a sign of a restriction within a line, the evaporater or condenser, or a sign of impending compressor failure.
In any case, if a restriction is found, it is recommended to flush the system entirely, replacing whichever componants are unable to be flushed, and recharging. If restrictions continue to occur, it is usually the compressor coming apart internally, and compressor replacement must occur.
For those of you that read through all that, congratulations. You now know the basic operations of an automotive air conditioning system.
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