I'm having a couple of issues with the a/c right now.

First, when I am at idle the a/c compressor won't stay on. I can hit the switch then get out and watch the compressor. It tries to lock and start spinning, the fans come on for a quick second, then the compressor shuts off and the fans turn back off. This makes me think it's not a problem with the compressor, but that for some reason the PCM is commanding the a/c to turn off. Low pressure maybe? Also - when I am driving at speed it sometimes comes on right away and sometimes takes a few minutes. If I come to a stop and idle, it will continue to blow cold until the compressor cycles off and back on, then it will do the same thing as listed above. When I am cruising, I can feel the air get warmer for a second or two then go back cold for awhile, then warm for a second or two, the cold again for awhile, etc etc....

Second, summer has hit hardcore. It has been 113 during the day the last few days. When I turn on the a/c during city driving, the truck starts to overheat. I can watch the ECT on EFILive go from 195 to 200 to 205 all the way up to 225 or 230 before I finally say f*ck it and roll the windows down and turn the a/c off. Then the temps will slowly drop back down to upper 190's. If I turn the a/c on when cruising on the freeway the temps stay stable in the mid-low 200's.

Anyone think these problems are related? Is it possible that just having the a/c system serviced and recharged will fix this? Any other ideas? Keep in mind that I have 120,000 miles on the truck and it's a 2001, a/c system has never been serviced.

 

I do lots of A/C work. Could be a sticky clutch, But my money is on a low charge! Shop around and get a free A/C check get some readings and report back. Manifold Gauges are the eyes into the system, Many variables...

 

I had the same problem at idle. I got a can of that 134a in a can with a guage, I hooded it up, but it showed High pressuer (possibly on the wrong port???) anyway after I did that, it started working fine dont know why though. Yesterday it started acting up again though.

 

I am no expert, but it sounds to me like the clutch is on its way out. I had a low charge in my last truck for a while and the clutch wouldn't even engage.

 

I vote for low charge.

 

My A/C does the on and quick off at idle you are talking about. It started doing it when I turned off A/C bump spark off. It only does it when I first start it in the morning. Once it idles a bit and warms up it stops. I think what you are seeing is a PCM related anti-stall. AC clutch comes in and the PCM sees that the engine will stall and it pulls the A/C back out.

 

check your pressure switch but like everyone else says you probly dont have enough charge to make it work

 

That sounds exactly like what mine is doing, so whats the fix? I was gonna bump the idle with A/C on up a little.

 

Unplug the cycling switch (the one on the accumulator) and jump the 2 terminals with a paper clip or wire. If the clutch stays engaged then, see if it's cooling good. I (gm technician)have seen a lot of bad switches, you can tap them and they will start working. If it still doesn't cool well with it jumped, you may be low in freon. Also make sure the belt on the compressor isn't slipping, the tensioners on these trucks are weak anyway and fail rather often.

 

I'm taking it in tomorrow morning to have the a/c "re-filled" or whatever you want to call it. If that doesn't fix it I will try the other suggestions.