No heat or air thru vents ... help?

Hi-

I can't figure this one out. When I switch the air or heat on, the air only goes thru the defroster vent. When I twist the knob, on the panel, to adjust where I want the the heat to come out, it doesn't switch. Is there a relay fuse or something I need to replace or, do I need to replace the switch panel. Please advise.

Thanks

I had the same problem with an F-150. The problem was that Ford hadn't opened up the vent shaft to let air travel anywhere else but through the defrost. If it's a newer truck this is most likely your problem. If the truck is older and it had worked before, than it's likely you broke a cable behind the heat control system, this might not be so easy to fix.

If it only blows out the defroster vent, and it blew out the correct places before, then it should be like Lupin1x said, either a cable that controls the damper in the heater box located behind the glove compartment or on newer trucks it could be a vaccum or electric controler that operates the damper. The damper moves and directs the air through different vents (like a door). You have to find out if it is operated by a cable, vaccum or electric. Good luck.