2004 Tahoe, with 175K. A/C blows 45 degrees and then randomly jumps to 95 degrees(ride around with thermometer in vents). Goes back to cold randomly, sometimes it works if I shut Tahoe off and back on but not always. Any help appreciated.

 

next time it blows hot, rev the engine up to 2500rpm and hold it there. if the a/c blows cold, the compressor is tired.
another possibility is low refrigerant levels. typically, the compressor will short cycle on/off with a low charge level.

 

Reved engine between 2500-3000 rpm's for 30 seconds. No change in temperature. Any more suggestions and thanks in advance! I also unhooked battery today for 2 hours to see if that reset blend doors or reprogrammed them but that did nothing. Actually now it blows 90 degrees all the time since doing that.

 

Do you hear/see the compressor running when blowing hot?
And, does it blow hot thru all vents at all settings on a/c?

 

Turn the AC on and feel the lines, one should be relatively hot and the other cold (exercise caution) if there is a reasonable differential, the AC is probably fine and its the blend door(s)... also if you have the rear AC check its function, if it works okay then the AC is probably okay and this will lead you back to the blend doors...

 

All vents do the same. Blows same temperature out of all vents regardless of temp setting. Checked temperature of lines and one is very warm and the other is cold. I replaced the main blend door under the dash just to left of glove box and problem persists. Blows hot mostly but randomly switches to cool for unknown reason. When it's cold....it's very cold but rarely last after I shut car off. Question...Could it be a temperature sensor, HVAC control module or something like that? IF so, how can I check before replacing?

 

Our 05 Sub needed a new control module when it showed a similar problem with erratic hot an cold cycling

 

I had the suspect that my car had a problem on the blend door actuator and now I have confirmed that, as it was an intermittent problem. Thanks for this topic.

 

Had diagnosed at dealership. They informed me all blend door actuators worked fine but I had a leaking compressor. If my compressor was leaking would it still blow cold at times? After Tahoe sits a while and you get in... A/C blows 45 degrees for a while but does not last long or after you take a short trip and restart it blows hot after you stop. Let it sit a while and goes back to cold. Just want to make sure what dealership told me is logical. Thanks in advance

 

someone said this!!


the system can have a slow leak and contain some refrigerant. they could charge it up and it would run fine until it leaks back out again(filling leaking systems for any but diagnostic purposes is against the law).
....the compressor runs until it can't suck anything in...the low pressure switch shuts the compressor off. After a few seconds off, the pressure rises and the compressor runs again. not much heat exchange occurs so the customer notices poor performance.