Is it possible for the trap door for the ventalation to be stuck in the open position? The reason I ask is that our 04 Burb. when the A/C is on, we somtimes smell outside air. The light comes on ,on the switch for outside/inside ventalation. I even thought that the switch was backwards, when the light was lite I thought the door was open. But its the same either way. Although the air temp. does seem to cool more with the swithc in the on position, but we still get fumes from outside sometimes. I will bring it in for warranty service for that and the rear back light on top doesn't work.