Climate Controls

Does it happen when you turn on defroster? If so, the A/C will automatically come on to remove moisture, may have something to do with it

The AC is not coming on. I know when I use the defrost, I can't use the circulating air (inside the car). But once I turn off the defrost, it will still switch from circulating to recirculating (bringing air in from outside).

OK. You may have has a vacuum hose come off the controller, and it goes back to default settings because it doesn't know what else to do or some other linkage problem. Sorry, that's al I can thinf of right now, check back here later after I can do some research, or somebody else will know. We will figure this out

Thank you for being so helpful. It shouldn't switch from one to the other, right? If I have it set on circulating air, it should stay on that control. Strange.

Its not a vacuum hose its how its programmed. You can only turn on the recirculating air on certain settings. I was playing with an impala that was the same way. They for the most part stopped using vacuum controls back in the 90s, by the early 2000's vacuum control were gone for GM anyhow.

But that doesn't help me to figure out why it switches automatically from circulating to recirculating when I haven't touched the controls. Thoughts on this? I'm wondering if it has some sort of climate control setting and it thinks it's warm, so it pulls air from outside.

You said it works fine on other settings correct? I have no positive answer as to why they do it but the way they are designed only allows recirculating to work on certain settings. Like david said its most likely something to do with the fact that the inside of your vehicle gets fog on it due to the fact that there is a lot of moisture inside your vehicle. More than outside the vehicle, to dry the air coming into your vehicle the AC kicks on and removes moisture by turning it into condensation. By turning the recirculating air on while the vehicle is trying to dry the air would cause the vehicle to take much longer in drying the air. If the inside is at 70%-100% humiduty which is where I believe fog forms and the AC can only remove 20%- 30% from the air then it would be taking air from inside the vehicle and putting the same air back in. You are replacing 85% humid with 55% humid vs pulling fresh air that has minimal humidity and the vehicle then dries it to less than 10% seems like the recirculating setting would be a waste. Fog only forms on the inside of the vehicle in certain conditions and in those conditions the outside air is always less humid than the inside air so it defaults to fresh air because it knows it will be easier and much quicker. read the owners manual.

I know when the defrost is on, it will only allow recirculating air (air from outside). But that doesn't explain why when the heat is on, and I have it on circulating air (air inside the car) that it will just automatically switch back to recirculating. I have read the manual, and it only refers to how the controls work when using defrost, etc. I guess next time I go in for service, I will ask them, too! Thanks for all your help!

Try changing between blowing on your feet and your face.