97 f150 My heater and air only blows out of defrost no matter what setting. Does anyone know whats wrong?

 

Depending on the set up of the system. On the manual systems cables somtimes break the gromets that hold to the controller or the door or also the lever it self binds or breaks. Now say if the controller was electric the motor could have seized then just leaving in defrost. You will need to start at the ac controller and follow cable and Etc. Personally it sounds like a popped cable or a bad controller

 

I forgot to tell you that when it started It would be blowing right through the dash vents like it is supposed to, but when my RPMs went up the defrost would kick on.

 

I had the same problem with my '97 about 4 years ago. I would have to dig out the receipt but I think it was a vacuum motor that had to be replaced.

 

did you do it yourself or did you take it in? If so where is it located?