What might I be missing? AC wasn’t working in my 2005 H2 – the cooling slowly started dying and then quit completely. I put it through the GM diagnostics including a leak test and a vacuum drop test – no leaks. The end conclusion via the diagnostics was that the compressor was bad (I did find a couple of fine metal slivers in the orifice screen, no brown residues were found). I replaced the compressor (with the Denso replacement), the orifice, and the accumulator. With these items replaced, I pulled a vacuum and recharged the refrigerant. Not surprising, the truck was once again putting out bitterly cold air, I could hang meat in there (or keep my beer cold). All was well until about 36 hours later, I started the truck and BAM, no AC – right back to where I started. It was pumping out hot air around 90-95 at the center panel outlet. What is confusing is that the AC worked perfectly as designed for about 36 hours – no problem, which implies that everything in the system was operating normally. Note that there were and never have been any DTCs thrown for the HVAC system. Any ideas (before I do a warranty return on the compressor)?

 

Does the compressor clutch engage?

 

check your pressure switches and check that the compressor is cycling.

 

Yes, clutch engages correctly and the LP pressure switch is fine and the HP pressure sensor is fine.

 

Is the compressor short cycling?

 

It cycles, but I'm not sure what you mean by "short cycling"

 

I had similar issues- would work perfectly & then would not. I ended up replacing the control unit in the dash & that resolved it. One of the quirks my existing control unit did was it would always default back to recirculation "off" - even tho it was on in prior use. That annoyed me also because with the age of the flap motors, it would be my luck it would fail in a recirculate "off" position...
Here is link for new replacement ( I tried the "used" option to save money on amazon, did replacement twice since the amazon warehouse one was worse than existing). New one has been working perfectly for several months,... Not saying 100% the issue, but it was in my situation.

 

I have that one in my 2003 H2 for about 3 months now and working okay. However, a buddy down at the Chevy dealer tells me that at times it's the only thing available, and it's not unusual to go through three or four before you find one that works properly. And once you find one that works properly, it's still not 100%. If you're doing any work on the PCM such as reflashing it, most likely you will have to unplug this unit to have any success. I've chosen to just live with that, not too much of a problem as long as you're aware of it.

 

 

You say you charged the system as part of the repairs you made, can you check the pressure and see that it still has freon and that the pressure is above 30psi?

Neal