Originally Posted by wilsons66604

The recirculate setting changes as the car deems neccesary. If it needs to work hard to get to the temp you are requesting, it stays in recirc mode. It's trying to be as efficient as possible. If you turn on defrost it goes to fresh air.
that said...I've notice my system set on fresh intake without any action on my part. I think it was because the cabin temp was near the temp I was requesting.