Hello to all. I just bought a 2008 Sierra and have experienced a problem with the HVAC system. When in A/C mode, either AUTO or manual, the air blows from the dash for as much as an hour and then I feel it blow on my feet and then it switches to the defrost vents. After this change happens I can't change anything on the control panel until I shut off the truck and start it again then everything works normally until the next time it switches on its own. I always turn the system off before I shut off the engine. I've also noticed that it switches from recirculate to outside air automatically. That I thought might be normal but now I am wondering about it too.
