Erractic Idle

I have a 1992 Chevy 1/2 ton with a 350. The air conditioning keeps "cycling" on and off causing the idle to go up and down and the motor wants to "stumble". The shop manual said it was possibly the accumilator switch which I replaced, and found no difference.

I have a 1992 Chevy 1/2 ton with a 350. The air conditioning keeps "cycling" on and off causing the idle to go up and down and the motor wants to "stumble". The shop manual said it was possibly the accumilator switch which I replaced, and found no difference.

Is the ac low on Freon/gas?
R-12 or R134a
On the AC we need pressure reading low and high side at idle and at 2K.
Also you need to check the IAC valve and pcm for proper idle control.
MT

It's R-12. I don't have any gauges however I removed the plug wire from the compressor and it idles fine. So I'm assuming it's low on freon. Since R-12 is hard to find and expensive I'll convert it over to R-134.

It's R-12. I don't have any gauges however I removed the plug wire from the compressor and it idles fine. So I'm assuming it's low on freon. Since R-12 is hard to find and expensive I'll convert it over to R-134.

If it will not idle good check IAC valve and IAC valve operation AND PCM FOR IDLE CONTROL.

On the AC it needs checked with gauges TO TELL IF IT IS LOW OR OTHER PROBLEMS.
MT

I had it converted to R-134 today. It was low so the system was evacuated. What is the IAC valve and PCM? I'm assuming the PCM is a control module, right? It's much better however the idle still doesnt seem right. The shop said it was normal, and ok. Thanks for the help.

IAC is the idle air control valve.
It is what controls the idle rpm.
The pcm is the engine computer.
It tells the iac at what rpm to set the idle.
Does it idle the same rpm with air on or off?
And at what rpm?

I noticed it does this when it reaches operating temp or close to it

I noticed it does this when it reaches operating temp or close to it
Got any codes?
Check the thng we have outlined for you to check.
MT

It's going to the dealer in the morning. Thanks

Went to the dealer, they found no codes. Freon was a little low (thats another issue, I had it changed over on Monday to R-134a). Now they say it's the wiring or the control head because the compressor won't shut off.

Went to the dealer, they found no codes. Freon was a little low (thats another issue, I had it changed over on Monday to R-134a). Now they say it's the wiring or the control head because the compressor won't shut off.

When you had it switched to r134a, did they replace the pressure cycling switch on the accumulator? See http://autoacrepairs.com/cycleswitchinfo.htm

//2000CAYukon

Explain the will not shut off.
And how they figure it is a little low?
What positions on control head will it not shut off.
On AC or defrost position the compressor should run.
If pressure gets to low or to high the pressure switches will turn it off.

What is the low and high side reading on AC with compressor running at idle and at 2K?

Drove the truck to work last night, it seemed fine. Drove home from work and the same "crap" all over again. Idle was up and down, truck stumbled, check engine light came on. I unplugged the connector to the compressor and it idled fine and check engine light stayed off. I'll see if they changed the accumilator switch to 134a. I put a new one in for 12 before I brought it in.

Drove the truck to work last night, it seemed fine. Drove home from work and the same "crap" all over again. Idle was up and down, truck stumbled, check engine light came on. I unplugged the connector to the compressor and it idled fine and check engine light stayed off. I'll see if they changed the accumilator switch to 134a. I put a new one in for 12 before I brought it in.

What code is being set?

//2000CAYukon

They found no codes at the dealer. I'm going to use a code reader from a friend, and see if I come up with one.

no codes, changed the iac now compressor doesnt run. test drive tomorrow

used friends code reader. Found code 44 ( o2 sensor ) lean. Changed sensor ran ok until temp went to normal. Check engine light came on and idle became unstable ( up and down ). Could this be a bad temp sensor. The code reader temp said 180, gauge in truck was 120 at best. I also noticed that when the code reader was plugged in the truck started to run bad, missing and raw gas smell.

Found a tech tip about cleaning off the control head with an eraser. So far that took care of it. It still has a hard start condition, then it runs rough for a while ( hesitates, stumbles ). The air compressor doesn't run all the time even with the control off like before. It problably needs a tune up. We bought it from the original owner and everything looks original.