Okay here'* a weird one: 2017 Traverse with ~57,000 miles on it today decides the AC won't cool.

- Compressor runs when I turn on AC or defrost from controls, stops when I turn elsewhere as it should.
- Compressor makes no bad sounds, and barely affects tach needle at all when it engages.
- Fans do not run with the compressor, but work fine to keep the engine cool.
- When the fans run to keep the engine cool, no change to AC temperature.
- Turn blend **** slowly back and forth to hot and cold and temperature changes appropriately with no strange sounds.
- Disconnect low-pressure sensor and compressor stops, reconnect and it starts.
- Remove compressor relay and compressor stops, reconnect and it starts.
- Remove compressor fuse and compressor stops, reconnect and it starts.
- High and low pressure pipes are hot at the connection to the compressor.
- Driving 60MPH for at least five minutes yields no change in AC temperature.

It'* like the compressor is being commanded on because the driver asks for cool, but otherwise it has forgotten the other steps necessary to deliver cool air.

Car was a rental for half it'* mileage, and all of that rental car mileage accumulated within its first six months of life. The rest came over the last 5.5 years, and hasn't missed a beat except for a bad coolant temperature sender a year ago.

Thoughts?

What are the pressures?

No pressures yet, had to troubleshoot on the fly on the way home from work.

Still can't fathom why the compressor is commanded on without the fans being commanded on.

Pressure switch?

I was thinking that too, but I disconnect it and the compressor stops. Reconnect it and it starts. I imagine the code goes something like this: If the pressure switch is reporting low pressure to the PCM, shouldn't the PCM say:

10 Start loop
20 If AC pressure switch circuit is closed, goto 30, else goto 10
30 If accelerator position is less than 100%, goto 40, else goto 10
40 Engage compressor clutch
50 Engage radiator fans
60 goto 10

. . . ?

Please forgive my pseudo-BASIC, this is about how I imagine the flowchart would work out for this function, but I don't want to fiddle with making a flowchart for this.

I was thinking that maybe it won't turn on the fans below a certain temperature, but the car knew it was over 80 degrees at the time so that'* not it.

You are going to need to see what the pressures are doing.

Yeah, it'll be a few days before I can get it to stop being driven for a few minutes. At least it'* winter. I pulled the compressor relay so it doesn't attempt to make things worse. Will report back with findings.

I believe If the PCM does not see a temperature of about 55 to 60 degrees it will not run.

It knew it was 80-someodd at the time, it was showing that on the entertainment screen.

Followup: I finally got it to sit still long enough to fiddle with last weekend. I had help from warm weather.

It turns out it was low on refrigerant. Filled it back up and it is happy again. So is its driver.

Now I'm waiting to see how soon it runs low again.

Looking around online, it appears that a lot of these have been low on refrigerant for a few years now. Seems like too soon for this to crop up. It took our Saturn Outlook over ten years and 175,000 miles to get to the same point.