Hello,
Just a brief explanation, I've had this truck since new, about 15-20 years ago it developed the dreaded belly leak on the compressor. I replaced the compressor and nothing else. Did the full vacuum and recharged. Now since that time the AC actually cranks out with front ac only down to 38* from start up and as long as you keep it going down the road, and I mean 100's of miles blowing 38, Now if you stop for an long time with it still running or stop and shut it off it will quite blowing out cold air for an extended amount of time, then it will eventually come back on and start blowing cold. Here are some more quirks, if I turn on the rear air it will eventually stop blowing cold air like above explains so I just leave off. Also if I start it in the driveway the air will blow cold just idling for as long as I let it run, no issues. Anyone have any idea on whats going on why it is so flaky. Pressures always seem normal with it being 35-40 lowside and 180-190 high. I sure would love to figure it out and have it act normal. Thanks.

 

I don't know about the "belly leak", and I should, as I specialized in auto-air. 38 F is a perfectly normal A/C outlet, in fact lower then many vehicles;35-40 and 180-190 is also considered normal for an R-134A A/C system. Could be the low-pressure side sensor, which is easy to replace and doesn't require you to recycle the refrigerant, but then I own a great Chevy 1998 K-1500.

 

The belly leak was from the horribly designed split case compressor, the seal in the middle of the case would eventually fail. The replacement one has lasted for a crazy long time. Your thinking it could be the low pressure side sensor? I will have to look up where that is located. Sounds to easy of a fix for the way things go for me. Thanks for your reply Henry.

 

Compressor relay could be heating up and failing, cools down and re-energizes. Check the prongs for discoloration.
I'll second the pressure cutoff being a thing to try also.
Check your air gap on the compressor clutch. if too large you may have to pull a shim out to close it up. The clutch does wear over time and as the magnetic clutch heats up it loses some ''strength''. I struggled with a high mileage Sables clutch doing that, ran great until it was on for a while, and it dropped out. Cool down and worked fine.

 

I'm not thinking the relay is the culprit because as I mentioned I can drive it cross country without stopping and it never cuts out, if I didn't need to stop for gas it would continue to work. The low pressure sounds like a possibility, I should just be able to jump that connector to verify if the switch is faulty when its flaking out. I'll certainly give that a try to see if thats the problem.

 

Ok big thanks to all who commented, I just jumpered the low pressure switch connector when it was in the failure state and the compressor came right back on. Hooray! Great that its not something more involved. Now I feel bad for dealing with it as long as I have. But in reality I really only use the truck to pull the boat and thats usually an hour and half trip one way, so the AC does good on that type of trip. It was just when I sat a light to long or stopped along the way it acted up. Now it will be good to have it functioning all the time.

 

Ok well maybe I got a head of myself thinking that was the sole issue. I have the new LP switch coming tomorrow. In the meantime, I removed the old one and totally flushed it with contact cleaner, was really full of that stupid dye. After toughly cleaning and blowing it out I installed it back on the truck. I then started the truck and hooked up the gauges and things looked like they usually do 35/190. After revving it up for several minutes I noticed the pressures climbing pretty good so I decided to run the gauges out of the hood and tape them to the windshield to see what the pressures were doing while driving. The pressure before leaving were around 35/200. As soon as I started down the road they both climbed pretty fast to around 50/300 and then the compressor kicked off like it has been doing, i dont know the exact pressures but they reached these for sure. This was the first time I realized those pressures were getting that high. I got back in the driveway and decided to let some coolant out as I was thinking maybe there is actually to much in the system. Then I took it back for another ride. This time the compressor stayed on the whole time even with me stopping and going. The pressures changed to 22/210 while driving and when stopped and idling, I then turned on the rear which I never do as it usually kicks it off quick, the pressures rose again this time while running at around 50/275, and for reference its like 95 here in florida right now. So riding around like this the pressures stayed pretty close to these figures and the compressor never turned off. I turned off the rear air for the rest of the ride home and pressures dropped back down and when idling in the driveway they read 40/250. Does anyone with AC knowledge think I should let out a little more coolant to see if those pressures come down more when driving or should I just have it evacuated, change out the orifice tube and dryer and measure the exact amount of coolant to go back in. I'm thinking now that switch wasn't really bad and maybe it was the pressures causing the issues. At what pressure do these switches usually kick off the compressor?

 

I think the high pressure cut off is at the 300 psi mark when it will cycle the compressor but when it cuts back on it will put it right back at the cutoff in hot weather quicker than you can feel cold air.
Most likely you were overcharged and letting some out got you back into the operating range.
Charge is done by weight; those little cans are not accurate. Shop does it by putting the 20 lb can on a scale so you can put the precise amount back in.
I've done a few systems on my vehicles; I have access to a scale and a vacuum pump.
Google up a 134A temp / pressure chart to see how ambient air affects pressures.

 

Yes I realize weighing the coolant is the only real way to get the right charge in the system, Like i mentioned in the first post I put this compressor on over twenty years ago and if I recall I just added the cans by what was needed, I didnt use a scale, and I think I have added a little more over the years thinking I was losing some. I know the best solution would be evacuate it all, while its empty change the orifice and dryer since they are the originals and be exact and weigh as I put it back in. One thing and I am not sure its normal but if I just use the front only it gets real cold like down to 38*, but when I turn on the rear it raised the front to the upper 40's, is that suppose to work like that?

 

I am not an expert in dual A/C system like your Suburban, but 22 PSI low and 210 high PSI isn't normal. 40-45 low and 150 to 175 PSI are the ideal pressures. The R-4 compressor is the unit with the belly leak. I've never seen one do that, but have heard of it. I think your notion to evacuate the system and change out the orifice tube and the receiver/dryer is a great idea, Brandon.

Edit: I'd add an ounce of PAG 100 oil., which is called for in your system. You can get a can of that at any auto parts store. Good luck, and let us know how it works out for you.