2016 GMC Acadia Normal Low, Excessive High Pressure

[bwthor]

I have a slow leak in my system. I had it at the shop and they were unable to locate the leak so they put dye in the system, and scheduled me to come back. This was a couple weeks ago. Yesterday, the car wasn't cooling as it should, probably 60-65 degree air out the vents, but only 75 degrees outside. Got home after a 30 minute drive, and hooked up the gauges. Low pressure was 42, so within range for 75 degrees (35-45), but the high was around 210 when the range should have been 150-170. I left it run for probably 15-20 minutes, and there was no change in pressures. Both cooling fans running normally, and the condenser was not plugged or dirty.

Looked up the symptoms, and found that normal low pressure, and excessive high could be due to poor condenser performance. I grabbed the garden hose and sprayed the condenser to cool it, and both low and high dropped below the expected pressure range for the outdoor temp, which was fully expected. I ran the car another 20 minutes, and expected the pressures to climb back up to their previous pressures, but they stayed low. There was no change in the cooling performance either. Since the pressures both remained low, I added freon to get the pressures back in range, and the cooling performance was again blowing cold as expected, and both High and Low remained with the expected range for the outdoor temp.

So, my question is, can anyone explain what was going on in the system that it seemed to be "stuck" at the high pressure on the high side? Things are working now, but my curiosity on how the systems function have me wondering what was happening with the system.

[JohnHere]

Low pressure was 42, so within range for 75 degrees (35-45), but the high was around 210 when the range should have been 150-170.

Contrary to the P/T chart, the low side at 42 PSI would result in an evaporator temperature of about 46°F and center-vent temperatures even warmer than that, which is why you weren't getting much cooling. The high side isn't that bad, but it could be improved (lowered) somewhat.

First, find and fix the leak(s), possibly originating at the compressor shaft seal. Then ensure that the charge amount is 100-percent correct.

Afterwards, if the pressure on the low side and the center vent temperatures revert to being high again, the compressor control valve might be the cause.

Does this vehicle have rear A/C and rear temperature controls, or is it front A/C only?

[bwthor]

Thanks for the reply, yes, it does have rear climate controls. It has already been fixed, I was just curious why it seemed to be "stuck" at the wrong pressure until I cooled the condenser.