I was under the hood of my truck yesterday and the ac compressor was spinning. The catch is that it was 0 Celsius and the AC wasn't turned on. I looked at the controls and the the fan control was on setting 1 and the temp was down all the way on the blue. The AC button light was not on. When I turned the heat up the compressor stopped. This cant be normal? Anyone have any ideas...

Defrost also runs the A/C compressor. You need to run A/C when your in defrost to get rid of the humidity in the vehicle.

My ac stays engaged in defrost, defrost and low setting and even right on low only setting (12:00). I have to turn mine counterclockwise just past the 12:00 low only setting to disengage the AC.

Wow I never knew that:o: I guess that makes sense, don't want humidity in the iar when you are defrosting the windows. Thanks guys.