I have a '92 C4 Coupe with an intermitent A/C problem. I've owned the car for 3 years and have always had the problem and am getting tired of it. Periodically the A/C decides not to work. As prescribed in the manual, I remove the radio fuse and the courtesy fuse for about a minute. It then resets itself and is fine...........for an undetermined amount of time. What is the reason for this and what is the fix? Any advice that you can give to enlighten me would be greatly appreciated. Thanks, in advance!

 

Assuming it's full of refrigerant, my guess is that you have a bad connection at the Low Pressure Switch. A/C works by boiling a low pressure liquid into a low pressure gas. As the liquid becomes a gas, it absorbs the heat from the air that's around it, making the temp of the air quite a bit colder. Regardless of refrigerant used, the idea is to make the process happen right at 32 degrees, so on the gas side is a switch which simply opens the electrical circuit to the compressor when the pressure of the gas drops below a certain threshold - about 25 psi if you car is using R12 - or at the pressure where you start making ice out of the moisture in the air that making it boil. With the compressor no longer turning, the pressure rises, and when it gets up to 50psi, the switch closes and the compressor comes back on. Though outside air temp has a role, as long as the supply is sufficient, the switch contacts will usually remained closed, the compressor will continue to pump refrigerant and the whole thing will stay happy right around that freezing temp (pressure). If it didn't work this way, the system could drop to a pressure that would cover up the boiler (Evaporator in a/c speak) in ice at which point no air is going to get through or out of the vents - or, since the refrigerant also carries the oil that keeps the compressor from self destructing, a low pressure situation might also mean there's a shortage of lube - or, turning the compressor on and off a lot is hard on it's components - for longevity, you don't want it shutting on and off very much. So your 92 monitors how frequently that switch opens and closes and if the PCM sees a lot of no voltage, then voltage coming from the switch, it uses that to sense it's low on gas. This shuts the whole thing down and spits out a trouble code and with a code, it won't let it run again until you clear the memory of the on/off device which is why your Manual instructs you to pull the fuse. But, if you know it's full (with or without a code), the place to look is the connector - it may be loose, or intermittently loose which tricks the PCM into thinking there isn't enough gas. So you can try to duplicate the problem by wriggling the connector around, or if that doesn't duplicate it and there isn't a low gas code, wait until the next time it happens and simply disconnect and reconnect the harness from the switch. If that makes it work, the connector or connection is bad. Some need a new connector - some a switch - the components simply have to stay together for it to work right.

 

Yikes! I forgot to tell you where the low pressure switch is. It's either on the the Accumulator - the tin can - or the Evaporator, at the firewall on the passenger side.

 

Thanks for the info. I really appreciate the help.

 

SunCr,

I always enjoy your descriptions of the details on AC operation.
Read them thru and thru everytime.

Thanks for taking the time to write'em!!

 

Having never owned a car where the a/c didn't break - glad to help!