I have an 02 F150 with a 5.4 V8 that has climate control. When climate control is off, warm air still flows from the Defrost vent. When temp is set to cool the cab via A/C (auto or max A/C), the air flow is only to the defrost vents unless the air temp is below 80 degrees outside or in the cab. Pushing the Vent button on the climate control does flow air to the panel vents but once the Auto or max A/C buttons are pushed it goes back to the Defrost vents. If the outside or cab temp is below say 80 degrees cold air does flow from the panel vents like it should. I removed the vacuum line from the engine intake manifold and pumped the vacuum up to 20 Hg. It holds but very, very slowly decreases over say a few minute period. With the vacuum pump in the same location and engine one, vacuum is lost completely and I can't hold any steady vacuum by pumping it up.

 

You may have a blend door actuator motor problem. It is electrical and has nothing to do with vacuum. Google "Heater Treater" and see what I am refering to.
Will Walker

 

All directional control of the outlet air is via vacuum motors. The temp blend door is only for temperature control.

 

I just check the blend door and actuator are working and in tact. The door moves freely by hand the the actuator motor moves back and forth. I can get hot and cold but only from the defrost vents. I think this is a vacuum problem. Back to the lines and connections i guess. Any suggestions?