Intermittent Short Cycling Causes?

[whocruiser]

OK, I had both of the big AC hoses replaced recently, system worked OK for a week or two, then started short cycling and barely cooling, classic sign of having lost the freon charge. Assumed it must have leaked out somewhere and would have to have them replace something else and refill once I could find the time to take her over to DMCFL again to find the leak. Today on my drive home from work it suddenly started normally cycling again and cooling properly. I'm thinking it might be a faulty pressure switch and/or the wiring/socket attaching to it. How failure prone are they, and is there anything else anyone can think of that might have the same effect? I'm REALLY hoping that is the cause, as it's one of the few bits in the system that I can actually change out easily by myself at home if I understand it properly. Any experienced thoughts or advice?...

[DMCMW Dave]

I'm thinking it might be a faulty pressure switch and/or the wiring/socket attaching to it. How failure prone are they, and is there anything else anyone can think of that might have the same effect? I'm REALLY hoping that is the cause, as it's one of the few bits in the system that I can actually change out easily by myself at home if I understand it properly. Any experienced thoughts or advice?...

The pressure switches are prone to failure, and even better, are cheap. The usual failure, though, is that they leak. Check and clean the wiring at the switch.

Also - check that the main cooling fans are working, if they stop working the pressure will take off and kick out the high pressure switch. Check the circuit breaker for the fans. You should also see the car temp gauge get hot, but maybe not as quickly as you notice the A/C not working.

[Bitsyncmaster]

I did what you did and replaced the two long hoses. It still leaked but took a few months. Turned out to be the short hose from the condenser to accumulator.

Was your system converted to R134a?

[whocruiser]

Fans are working normally and temp gauge is working normally too. No conversion, still on R-12. I didn't even know there was another hose in there, I thought that was all hard piped other than the two big ones off of the compressor. I guess that's another likely place to look if the charge does leak out. If it acts up again I will try hitting the plug & socket with a shot of contact cleaner. I do have an earlier car (1150) and they changed out to the newer dryer to match up with the newer hoses, does this also change the pressure switch setup in any way that might cause this result? And should the new dryer have come with a new pressure switch already attached or would it be standard practice at DMC to reuse the old one? (I honestly don't know if they did or not, and it's hard to tell without removing it for a closer look, but I generally trust Kevin to have done what he thought was needed, he knows his stuff.)

[mluder]

Anyone ever experience this... I was driving with the interior fan running. AC off just fresh air coming in. Pull into my garage and shut off the car... Lo and behold, the fans are still running. I turn the mode selecter to off and it eventually turns off. I tried to replicate it by turnung on the electrical - didn't actually fire the engine. Turned on the fan and shut the engine off and it did it again.

I don't get it... With the electrical system off, the fans should not physically be able to run, correct?

Cheers.
Steve

[Bitsyncmaster]

Anyone ever experience this... I was driving with the interior fan running. AC off just fresh air coming in. Pull into my garage and shut off the car... Lo and behold, the fans are still running. I turn the mode selecter to off and it eventually turns off. I tried to replicate it by turnung on the electrical - didn't actually fire the engine. Turned on the fan and shut the engine off and it did it again.

I don't get it... With the electrical system off, the fans should not physically be able to run, correct?

Cheers.
Steve

If you have my solid state fan relay, it will continue to run for 20 seconds after you turn off the engine. I think the fanZilla will run a few seconds longer.

There was a unit that could fail and never turn them off. Not sure who sold that unit.

[mluder]

If you have my solid state fan relay, it will continue to run for 20 seconds after you turn off the engine. I think the fanZilla will run a few seconds longer.

There was a unit that could fail and never turn them off. Not sure who sold that unit.

I believe I have the fan fail relay mod that was part of a service bulletin if i recall correctly, however, I'm talking about the climate control fans continuing to run, not the engine cooling fans.

Cheers.
Steve

[Bitsyncmaster]

I believe I have the fan fail relay mod that was part of a service bulletin if i recall correctly, however, I'm talking about the climate control fans continuing to run, not the engine cooling fans.

Cheers.
Steve

That would sound like a sticky relay.
Does it only do it if you leave the fan switch on?