I just purchased a 2011 GMC Acadia about 2 months ago. Tonight it was raining and 37 degrees. All the windows were fogged up when I started the car. I put the climate system on defrost but as the manual states the A/C did not go on because it was below 40 degrees. It took over 5 minutes to defrost the windshield. The rest of the windows were still fogged up. As I drove off the car had a very difficult time keeping the windows clear on such a wet and humid night. Early that night it was 40 degree. When I turned the defrost on then the A/C went on and all the windows in the car were clear in 10 seconds. None of the foreign cars I have owed shut the A/C off like this. I also don’t recall any of my dad’s old GM cars doing this as well. Do all GM cars do this now and why? It seems like a safety hazard.
Most cars will disable the A/C somewhere between 30-40 degrees. It’s hard on the A/C to run when it’s that cold, and there’s little benefit since the outdoor air is as cold as the A/C can get, plus (on non-rainy days anyway) the air doesn’t hold as much moisture (which is why you so easily get static shocks), so the dehumidifying effect isn’t necessary. (and wouldn’t work as well anyway)
Look at it this way–when the temps are close to freezing, what good would running the A/C do? The A/C is designed to shut off when the evaporator (the part that gets cold) starts freezing up, which would occur very quickly since the temps are already pretty close. It would be difficult to dehumidify the air too, since the temperature differential is so close.
My 2000 Blazer disables the A/C at low temperatures, but the manual does not specify a temperature. So, the feature has been around a while.
This has been a feature for at least 20 years but the temp is usually 35 degrees to prevent freezing up the AC.
Well, I guess my complaint would be the 40 degrees is too high to turn off the A/C. I have never owned a car that had trouble defogging in the conditions I encountered last night.