I just purchased a 1978 F150 and the ventilations system does not work properly.

The switch that controls the air flow to different areas (hi-lo, vents, etc...) does not work in that the air never moves from coming out of the defrost vents no matter where the switch is moved to.

What would cause this? bad switch? no vacumn? vacumn motors not working?


I have checked a lot of the vacumn lines and the rubber appears to be good.

How does the motor create the vacumn in order for the system to work? Could this system, whatever it is, be the culprit?

I've also noticed in Chilton's there are two motors in the lines, one for heat and I think the other is for defrost?

The truck is very sound and in good shape, but needs attention w/ weatherstripping, and other seals.

I pulled the switch system out of the dashboard and move the lower switch back and forth. I saw movement by a small white plastic "wheel?" but again, I didn't really check for a wire.

 

defrost is the fail safe I think. Someone told me why those do that but I can't remember now. Many moons ago. The truck I learned to drive in (a 1977) did that too.