It's probably the fresh air door. Remove the glove box and look at the actuators as you manipulate the controls. You might see that one of the connector arms has come loose -- or that a part of the plastic of the fresh air door has broken off. The actual flap of the door is behind the glove box, the actuators are just to the left of the box. On mine, the actuator arm had come loose, so it didn't move the door open or closed. The door was constantly in the open position. I couldn't figure out how to reconnect the arm to the door, and it appeared all pieces were there (hopefully, someone here knows what to do, or you can figure it out). I took a shortcut route and took a piece of household 14/2 wiring and bent it into an 'L' shape and closed the door, left the wire pressing the door closed, and then used a small 'C' clamp to hold the wire in place. Free and easy fix -- I've heard some people use a screw to hold the door closed. Both ways bypass the actuators, so the door no longer works as it should. But, then, I'm on the west coast and I don't really need a fresh air door. It's been over 6 years, and my 'fix' is still holding.
Removing the glove box is not hard and gives a good view to take a look at what is actually needed.
