Why does my a/c only blow cold from the defroster vents

Hi,

The HVAC blend door may be stuck or the blend door actuator motor may be faulty.

There are plenty of videos on YouTube showing how to replace the temperature blend door actuator but none seem to be for the directional blend door for your year range F150.

You may have better luck finding one. Just search for (insert year model) Ford F150 HVAC blend door actuator replacement

If you cannot find any either you may get some clues as to where to look for your actuator’s location by viewing some of the videos for later year models.

Sorry that I cannot be of more help, but it may be a start.