Fellas
My air vent select is changing from panel to defrost on its own. I set it to panel,ac,floor panel. Then after a while the **** will be on one of them. Then the air will switch to defrost. I am thinking i may have a vacuim leak? Any thoughts

 

Yeah deff a leak. Mine was a hose had came out of a grommet under the dash around the passenger side floorboard. I dont know exactly where it was bc my dad fixed it when i wasnt home. Only difference is mine was stuck on defrost and wouldnt change.

 

Yep, a vacuum leak. In default the heater control will go to the def mode automatically (without sufficient vacuum).

 

Numerous threads on this issue. http://www.f150online.com/forums/hva...buildable.html