AC Help on 2004 Suburban
 

I am at my wits end. Here's the saga - system wasn't cooling well this summer. Charged it up but high side never went up, until the compressor seized up and puked refrigerant. Oh well, figured I'd start with a fresh system. Sticker says 48oz R134a and 11oz oil.

1. Disassemble and flush entire system with flush solution until it flowed clear, then dry out all components with compressed air.
2. Replaced all seals
3. Replaced accumulator, orfice tube and rear expansion valve, compressor
4. Placed 9.6 oz PAG46 throughout the system during reassembly (new compressor already had 1.4oz pre-filled)
5. Placed vacuum on system (my Robinair pump pulled 25hg/in for 20 minutes). Let it sit for another 20 minutes and 0 vacuum loss
6. Filled with exactly 48oz R134a
7. My current gauge readings at 75 degrees ambient are 30psi low and 140psi high. Output from cabin air is ~50 degrees which isn't great considering the weather. I have cleaned the condenser and I've had a look at the evaporator with a phone jammed up in the box - there is a LITTLE debris near the bottom of the box I will try to get out however it doesn't appear obstructed at all

So the system isn't performing great - I COULD add more freon based on the gauges, which I'm reticent to do because here's something else that is going on as indicated by the following:

• I've driven the truck around a bit with it charged as is and a couple times I've heard a horrible groan/squeal from the rear passenger area outside - 99% it is refrigerant escaping past the seal at the rear evap connector which makes no sense at the pressures I'm seeing and it only happens right when the truck starts up after sitting - while driving I don't notice it. Wouldn't this indicate overcharge or is it possibly a bad seal?
• The compressor NEVER turns off. Even if I turn off the AC button, so long as the fan is on the compressor is on. It also is not cycling on and off during normal function - this doesn't seem normal? Could I perhaps need a new AC control panel too? What is a good way to test the high pressure switch?

Can anyone help me out? I'm really getting frustrated as I've done this work on a couple other cars in the same way and had no issues. I'm at a loss as I've done everything according to the specifications and nothing seems to be right... and the Facebook GMT800 bros are taunting me with pics of their vents at 32 degrees :mad:

Typically with a modern parallel flow condenser, these get replaced when a compressor seizes, since that type cannot be adequately backflushed.

What did the orifice tube look like? Debris?

No debris and the condenser flowed just fine when I ran flush through it, didn't seem to be stopped up at all.

I'm just not understanding why the compressor isn't ever turning off when the fans are enabled, but I don't have access to another truck to know. Is it possible a failed temp control panel is telling the AC to defrost even though its on upper-vent setting only?

With parallel flow condensers, the liquid can take alternate paths so backflushing does not work well (serpentine condensers can be backflushed). That said: it is possible that your compressor seized and little to no particles made it through to the condenser.

Looking at your numbers: 48 oz (four full cans) and your high pressure of only 140 psi - which is low - you may want to consider an additional can of R134a.

Remember: R134a, correct type and amount of refrigeration oil, and UV dye are acceptable. NO sealer or refrigerant containing sealer, EVER !!!

Compressor never turns off, pull the comp. relay and see if it's stuck closed. You can even swap out with another one the same size. Moving the relay can unstick them also so they work fine in another position also.

It does cycle off if I put the blower to 0 on the control panel, so I don't think its a stuck relay. But if the blower is ON, even if the "AC" button is off, the compressor is turning.

I would suspect the control then if it turns off when blower is off.
Really need the wiring diagram to check everything out before parts swapping.

OK so I had the system evacuated to "start over" since I had a horrible groaning when it was getting near load previously. I replaced the rear evaporator seals (that's where I was hearing the awful groan from). I put the system on vacuum for about 45 minutes and it held 27hg for about an hour with no loss.

So I started SLOWLY filling the system. I'm at about 36oz now of the 48oz load. I am filling it by pressure, not weight just because doing it by weight last time didn't work. I've determined that having recirc on forces compressor on, that's why it wasn't turning off when I turned off the AC button. And while I was filling, the compressor did seem to cycle on and off.

Today I was hoping to finish it up. Hooked up the gauges, static PSI was about 70 on both gauges. Turned on the A/C and low side hovered around 60 and high kept climbing - got all the way to 400 before I could shut it off. The compressor never shut off during this time (shouldn't it???). Didn't hear any groaning/escaping of gas. The other thing I noticed while filling was a LOT of condensation coming from the rear evaporator ports. Not sure what this is indicative of, but the rear air definitely got colder than the front while I was filling - like the rear was around 50 degrees when I was at 24oz refrigerant and the front was still lukewarm.

I'm at a loss now. The system's refrigerant circuit isn't computer controlled, right? The only "valves" are the orifice tube, which is fixed, and the expansion valve, which is mechanical. What is causing the pressures to rise so high??? Remember, I've had this whole system apart, flushed every tube and component, and everything seemed to flow normally.

I'm at a complete loss... none of this makes any sense unless the new expansion valve is faulty in the rear? The only other thing I can think of is the compressor came with more oil in it than it said and thus there's an oil overcharge causing the expansion valve to block up? But an oil overcharge normally leads to high low side PSI too which I'm not seeing when I was filling it (other than today when I first started it up).

It should have a high-pressure cutoff to turn off compressor. Not sure on your truck but my 09 Malibu and my '11 Tahoe have it.
Low side high is a restriction in the low side. Some junk may have come loose and plugged the orifice. I would think the initial low charge is getting sent to the rear first since the front is not getting cold first due to a restriction.