TheAC/heater in my 2000 Expy will only blow air out of the defrostand floor. When I switch the dial to panel or AC it continues to only blow air from the defrost. All the other dials on the unit work fine, the ac blows cold and heater blows hot. Any input on how to fix this would be greatly appreciated.

 

I have a 98 expedition. We recently had to have the heater core replaced. I was going to do the work but was completely discouraged by the amount of dash work that I would have had to do. Anyway, it cost about 500 bucks to have a shop do it. When they did the work they replaced the mixing door assembly because it was cracked and would have eventually stuck in one position or another. I would suspect that may be your problem.