A/c Problems In 94 Corolla - Corolland: the Toyota Corolla Forums

I'm having a problem with my A/C. The a/c works fine in when driving nearly all of the time, the problem occurs when I sit and idle and run the a/c for over an hour (... I have a 2 hour break in my day with no option of returning home). After giving the compressor sufficient time to heat up, the clutch begins to cycle, engage/disengage, on for a second or two, off for several seconds. So obviously the a/c starts blowing warm air.

What would cause the clutch to start cycling like this after becoming sufficiently warm?

This is actually a pretty normal behavior, especially when the temperatures start to creep up there. When you sit stationary, there is minimal air flowing over the condenser, thus the cooling efficiency of the system is not optimal. At speed and higher RPMs, there is more air flow through the condensor / compressor is working optimally - so that you can get decent cooling.

Most don't idle the car long enough to see this happen - usually takes a good amount of heat soaking to get it to warm up to that point. Nothing really qrong with the system, it could be blowing ice cold air every other time, but just pump out luke warm air when sitting still for extended times.

If the on-set of warm air is pretty quick - could also be a sign of lower refrigerant levels - but have the system pressure tested first before you attempt to add more refrigerant. Too much in the system (overfilling) can ruin seals over the long run. Double check that the fans are running and pulling fresh air over the condensor - bent or damage blades or obstructions in the condensor/radiator fins themselves.

Thanks for the info, fish.. but unfortunately the problem has just deteriorated. I connected a pressure gauge to the low end, but did this while it was cycling so I couldn't get a good read. According to my ambient temp and the instructions with the pressure gauge, the pressure should be about 50psi (assuming the clutch is engaged).

Now, driving the car today, the clutch will engage/disengage constantly, starting from inside a minute after turning on the A/C. So it's doing it without sitting idle.

First question; What should the pressure be while the clutch is NOT engaged?... Asking this because I get more time while not engaged, only a second or maybe two while engaged, so I'm not sure if I'm getting an accurate read while engaged.

Second question; What are the possible reasons for the clutch cycling constantly, now without sitting idle heating it up.

Third question; Could I possibly have a bad clutch? ... Hoping so since that seems like an easier and cheaper fix that I could do myself.

The only fan that I know about is the radiator fan on the driver side. Can you direct me to the condenser and fan? I don't remember seeing them.

EDIT: I should also note that turning on the A/C while driving has a noticeable performance effect on the engine when the clutch engages. Not significant, but noticeable.

DOUBLE EDIT: I checked the condenser and fan. Condenser has some wear, but it's been through 250K miles. Fans work too (both radiator and condenser fans).

Thanks for the help.

if its overcharged your compressor will cycle on for a very short amount of time and you won't get cold cold air. similarly a heat soaked AC system causes pressures to spike and problems like that, since pressure and temperature both rise together. other issues could be present with the metering devices or even the compressor itself.

Could be a bunch of reasons why the system is short cycling. Since the condition has deteriorated / changed, makes diagnosing it that much harder. Could be anything from a bad clutch, bad ECT switch, too much charge, too little charge, bad compressor lock switch, faulty HVAC control, bad A/C amplifier, faulty relays, etc.

Pressures for the A/C system - low side is 0.15-0.25 MPa (22 - 36 PSI), high side is 1.36-1.55 MPa (200 - 225 PSI) - but those are read while the engine is running, system engaged. When the compressor is not on, can't really see what is going on.

Things that are normal - when the A/C engages, it should load your engine down somewhat. The engine should respond by increasing the idle speed - but on a smaller displacement engine like the Corolla - the A/C system could easily use 20%-25% of the available engine power. Only have the fan for the radiator (some had two side by side fans) - the fan pulls the air through both the condensor and radiator. Of course, at speed, high pressure air under the nose of the car will help keep things cool.