AC Warm at low RPM's and cold at higher RPM's
 

I have a 2005 Chevrolet Suburban Z71 optioned with rear AC and Auto Temp Control. When at idle the AC blows warm but if you raise the RPM's to over 2000 it'll blow cold air. The system has been checked for leaks and there are none. The system has been fully discharged, flushed, tested and re-charged to spec with no improvement. The orifice is clean and everything appears to be in check but at idle the AC compressor and fans are shutting down; as soon as you increase the RPM's they kick back on. Recorded pressures at 22C/40% humidity are 50 low and 150 high. The HVAC Control Module was replaced and dealer reprogrammed. Anybody have an idea what the problem would be?

textbook tired compressor.

trottida: Welcome to the forum.

Agree, the suction pressure is pretty high.

That's kind of a relief to hear as that is what is being changed out today. I had my doubts and felt like my mechanic was throwing parts at the problem. The electric compressor fan shutting down at lower RPM's didn't make sense to me. I would have thought that they would continue to run along with the compressor but they both shut off within 30 seconds of hitting idle. It was originally thought that the problem was HVAC Control Module and it was replaced; I have a sense that was a miss-diagnosis that cost me $350.

are you saying the vehicle uses a electric rad fan and not a clutch fan

Yes, the 2005 Suburbans have two fans that run in tandem. Both are electronically controlled and no clutch. Here's what they look like....


https://cimg3.ibsrv.net/gimg/chevrol...24d09578e7.png

The weather here hasn't been warm enough to test the new compressor so I'm not sure if replacing it resolved the issue.

I would also say yep weak compressor, replaced the one in the wife's minivan a couple years ago for the same symptoms.

Just a followup...

Given that the original compressor spent it's first 8 years (136K mi) in Texas I figured that it had a good amount of time logged on it and was probably tired and therefore I succumbed to replacing it even though it cooled at higher RPM's.

I ordered and replaced with OEM parts the AC Compressor, receiver dryer, orifice tube, AC belt and AC belt tensioner. While I think it is working notably better at idle, we haven't had any decent weather to stress test it yet. I'll give you an update weather permitting.

So we had 27 C weather yesterday (according to the ambient temp sensor) and I was able to stress test the AC System at 32% humidity. At idle the front center vents (driver and passenger) were blowing 27C whereas the front left AUX AC vent was blowing 20C. When I increased the RPM's to 3K the front center vent dropped down to 22C. I'd say that there is still something going on. Not sure where to go from here but because the condenser is working for the rear AC I wouldn't think that was suspect. The only other thing it could be is the front evaporator. What does everyone think?

I was told to measure the inlet and outlet temperature differential on the evaporator if accessible. It could be an internal bypass leak in the evaporator core.