coach do you have rear air? elvato has something on this but cant find it right now. but it seems the plastic gears strip teeth off.
http://expeditionforum.com/showthread.php?t=13543&highlight=blend+door
from joezek
I bought my 03 with rear a/c broken and front worked great. Thanks to help from ELVATO I got it working again.
In my case, and most other people's, the two actuators that control temperature (blend door) and ceiling/floor vents both break. There are tiny little plastic gears inside the actuators and they break the teeth off. Then the blend door gets stuck on full heat, and the air gets stuck on either ceiling or floor.
Those actuators are expensive as hell, but I got the gears dirt cheap (free) and completely fixed the problem in about 2 hours. You could also just take the rear a/c compartment apart and manually set it to full cold and then not worry about it. That's what I did before fixing it.