I have a 2005 Ford f150 and I can only get air to come out of the vents blowing at my face, it doesn't matter what setting its on I can't get defrost or air on my feet. Does anybody know what it is I need to replace?

 

There's two things that normally cause this.
1. The vent selector motor is shot. With the key on and engine off, listen for the motor moving the door when you cycle the switch between face/floor/defrost.
2. The more popular reason is that a peice if foam has fallen off of the vent door, causing it to be jammed. In the 2004-2008 section of the forum, do a search for this. There are a couple of guys who have done some write ups on how to fix it.