It sounds like you have a vacuum leak issue. The vent doors are actuated by engine vacuum. If the vacuum is weak, the vend doors will not open and close properly.
Check under the dash for vacuum leaks as well as under the hood (supply line). If you are lucky, with the engine running, you may hear a hissing noise.
Let me know what you find.
Sunday, October 27th, 2013 AT 1:39 PM