Is there a minimum outside air temperature for the A/C compressor to operate? One evening, we entered a somewhat damp car and the windows were fogged up. The front defroster did not do much good although it blew air (which was cold). Normally, the windshield would soon clear since the A/C dehumidifies the defroster air. I noticed the outside air temperature was 36 F and it was raining outside. I am wondering if this was too cold for the A/C to come on.

 

No, it should operate in Defrost mode to do exactly what you wanted it to do. Something isn't right. Any other symptoms anywhere else in the HVAC system?

 

There is a minimum outside air temp where the compressor will not turn on although I would think it would be hard to find that temp in large parts of California. The AC system will not reduce the evaporator temp below freezing since there is a chance of the unit freezing over if the outside air is humid. Usually they don't allow the evaporator temp to go below 36 degrees. This is directly correlated to gas pressure in the AC system so once the pressure drops to that level it will shut off the compressor.

The AC controller can also keep the compressor from running. I ran into this problem a year ago. I took my car out on a cold spring morning and ran some errands that required short drives between places with the car parked for a while. While at the last place the outside air temp went from 40 to 50 and the sun heated the inside of the car. When I started the car the outside air sensor reading was still 50 and the AC would not cool the car. The outside temp reading stayed at 40 for quite a while and I took the car to the dealer and found that the operation was normal. GM doesn't update the outside temp very often when driving at low speeds so you have to put some miles on the car or get the car above 50 mph for a few minutes to get it to update. I left the dealership thinking what a bunch of BS but when I hit the highway and got over 50 the temp updated and the AC came on. Since then I have noticed that my 08 Malibu does the same thing. I am pretty sure my 03 Tahoe doesn't do this and I know the 03Z didn't do it so it the newer cars are using a different design philosophy.

Bill

 

Interesting Bill. I understand what you are saying but I've never encountered it with any of my cars. Just lucky maybe.

 

Thanks. I recall something like this from the C5 forum some time ago but I never had the problem in my C5. This was an unusual night. We had a cold storm from Alaska but it was just a little too warm to snow. The display showed 36 F and it was humid in the car due to our wet clothes and it was raining outside. It was like the days before air conditioning when you had to wait for the engine to warm up so you could defog the windows. This is not going to be a common occurrence - maybe never again.