Automotive Air Conditioning Information Forum

Hey guys 2015 Tahoe with front and rear climate, put compressor, condenser, front and rear expansion valves in as previous compressor locked up, put about 3 ounces pag oil, filled Freon .920kg as it calls for, wired thing is when front AC is on pressures are pretty good, around 45psi low- 220 high at 90*f ambient. Once rear comes on low goes to 60psi- high goes 180-200psi. The front will cool pretty good without rear turned on, but as soon as rear comes on the front EVAP temp goes to about 55*f. I went ahead and warrantied compressor and both expansion valves just to ease my mind but I’m stuck at the same pressures and am at a loss.

From the compressor failure, it's probable that debris is still partially blocking the system.

Did you get a look at the old oil while replacing the components you mentioned? If so, it was probably black in color, which would require a thorough system flush. Then, new oil would have to be added to the clean and "dry" system according to the manufacturer's specifications, evacuated, and recharged into the well-held vacuum.

Unsure whether you did all of that.

Does your vehicle take R-134a or R-1234yf?

(I think you mean "weird" )

After having had rear ac for years in various vehicles, they do not cool well at idle as the compressor simply does not have enough BTU capacity at idle. You need to check your pressures at 2,000 rpm. I run the rear blower fan on low speed even when nobody is in the rear of the vehicle. If you are expecting it to be ice cold at idle with both blower fans on high speed, simply not how a factory GM vehicle with rear ac performs. That being said, my 97 Express van cools well enough that even on a 110F day, both blowers can be on the 2nd notch up from low and the interior comfortable. My 97 van has a PCM controlled GM dual electric fan setup for a ~2004 Deville retrofitted on it and it will sit around 40-45F at idle provided the front and rear blowers are not on high speed. In 110F with both blowers on high speed 50-55F at idle is about the best it will cool. Similar pressures to what you are seeing. That is also cheating a bit as my 97 has a cammed 383 in it and a looser torque converter and idles at ~780 rpm. I also have the engine cooling fans enabled at a much lower pressure than GM enabled them. Stock from GM the high speed fan on the 2005 trucks and SUVs my PCM is from was not enabled until 350 psi. Mine now enables at 210 psi and low fan speed is active at 190 psi rather than 260 psi. When I get on the highway even with blowers on high speed it will cool until the vents reach low 30s and high 20s before the compressor cycles. My 2011 Pathfinder, 1999 Tahoe and 1983 G20 van all had similar performance. The dual ac setups lag a bit in cooling idling around town but perform very well at highway speeds. At highway speeds they would all freeze you out in about 5-10 miles.

JohnHere wrote: Sat Aug 30, 2025 12:25 am Does your vehicle take R-134a or R-1234yf?

I believe all 2015 vehicles had R134a.

IT IS FIXED. The oil from the failed compressor was still good color, no Black Death, I pulled receiver drier from old condenser and there was some metal in there, did the flush.
The ultimate fix was I dropped it off at dealer to get diagnosis since they were doing free diag. They determined compressor was weak and I didn’t understand. Talked with the tech and since it wasn’t an AC delco compressor that was specific for a Tahoe the compressor didn’t have the volume required for dual climate. The part number for Tahoe compressor is only for Tahoe…. The part stores ( Oriellys, Advance) compressors fit anything with that engine, in this case all trucks. I bought the 500 dollar compressor and put it on once I got home, ice cold AC again.

Appreciate your following up with the solution.