Wild high and low A/C charge pressure issues, with intermittent cool air. '05 Z71 Front & Rear A/C

[kylebnoris]

Alright gentlemen,

I'm slowly picking away at this '05 Tahoe.

We threw a belt on the old compressor with a new idler puller because it was seized and the clutch killed itself. Given I had no leaks, and cold A/C instead of replacing the clutch we went ahead and replaced the Compressor (Same price) with a cheap UAC unit for $120. "If he dies he dies"

I know I know, change the filters, check the condenser (it's fine, fins look okay etc.)

So here is my weird issue.

added the correct amount of refrigerant (after a long vacuum down, with the correct amount of PAG46 oil etc, and what I thought was 2.7lbs, I even used a scale.

I found that with the Rear A/C and the front A/C both at full blast, my pressure started a bit too high,

86f with humidity at 70%

Blows Luke warm.

so according to various un verifiable charts,

35-45psi low side and 160-215psi high side is where I want to be roughly?

Well when the rear a/c is on in the rear full blast, I get cold air, about 76f and 65f driving.

This is after idling for about 10 minutes and the E fans kicked on and it settled here,



Cold air (not as cold as I've known GMT800's can get tbh) but what gives? when I switch to front air only the pressure drops then my air gets hot.

Rear A/C off and my pressure is low on both sides with warm air but the compressor is still running,

I did activate the Blend door recalibration (Key on Engine off, set A/C to auto, key off, remove HVAC fuse from box under hood, wait a minute or so, reinstall fuse, key on engine off, ac display defaults to 74, and runs through all blend doors, and temps, ends on heat, wait two minutes during, then key off, then key on engine on, viola, all my blend doors are recalibrated and now functional) because my blend doors wouldn't respond with the engine on. could probably have done that with my scan tool but I'm four beers in after a compressor swap, I take gasket, fuel injector test and replacement etc, I'm tired lol.

So now that I've got that fixed, I'm assuming I've got air in the system? I'm tempted to re-evacuate the system, pull a vacuum, and then re- add by weight again. I'm assuming one of these ****** cans from the parts store had some issues or something.

Or maybe it's elsewhere. Also I added UV dye, no detectable leaks yet.

Alldata is down right now so I'm here. Thanks for any help!

 

[kylebnoris]

I'm convinced my procedure to add refrigerant was flawed, so I'm going to spend the $40 on 44oz of Super tech pure r134a from wally world tomorrow, evacuate it, vacuum it, and then recharge it, by weight.

Do I leave the rear A/C running though during the process? that's the real question since it clearly makes a difference lol.

 

[justirv]

I'm convinced my procedure to add refrigerant was flawed, so I'm going to spend the $40 on 44oz of Super tech pure r134a from wally world tomorrow, evacuate it, vacuum it, and then recharge it, by weight.

Do I leave the rear A/C running though during the process? that's the real question since it clearly makes a difference lol.

Whenever I open up the system, I change out the accumulator/filter dryer. A nitrogen purge before deep vacuum will help to flush out non-condensibles, if available. Charging should be done with front and rear on. I don't recall the exact weight of the charge, but it might be closer to 50+ oz. Double-check on that spec please. I know with my front and rear, it is very touchy on weight, I'll have no cooling, I'll add an once or so, waiting 10 mins each time, then all of a sudden, everything is great.

 

[kylebnoris]

Running into a wall with the EBCM, but made another thread for that specific issue.

Going to recharge by weight this Wednesday when I get time and report back here. If she's all solved I'll try and detail out my procedure for future folks with the same issue