I'm having a problem with my 05 xlt, the vent fan power control is working and the temp control is working fine but when I turn the **** to defrost it keeps blowing out of the front vents and not the defrost vents. For a while it was making a real slight rough sound that would vibrate the gas and brake pedals when I would turn it on defrost, but today it was not doing that anymore.

Does anyone know what could be causing this problem and what do I have to do to fix it???

i have the same problem on my 05 f150 fx4....anyone know what is causing this?

Blend door, do a search on it, that is most likely the problem