My heat/cold knob would not work- it was stuck on full heat and this was terrible in the summer. Ford wanted $1000 to fix it because they have to replace the whole heater plenum, pull the whole dash out, take out the passenger air bag, and drain the A/C. Did some research found out that it was the blend door, it has a plastic type fitting that a motor (behind the glovebox) turns and adjust the hot and cold air. Anyways this door was broken at the point where the motor turns it so it was stuck in one position. I did some research and found this

http://chrisfransen.com/Ford_Blend_Door_Fix/index.html

I bought a new door ( he didn't know you could get one at the time) , anyways using a little saw and a dremel and a lot of swear words and a mirror trying to Dremel the bottom out of the plenum I finally got the old door out and put the new one it and sealed it all back up with duct tape because I didn't want to get silicone on the door and have it break again. Took about 3 hours to do a good job. I pulled the front seat out because im pretty big and don't fit in that small space very easily