My heat selector switch doesn't seem to be working properly. It blows out the defroster no matter what setting I put it on. I have 18 lbs of vacuum off the motor and 18 lbs at the switch. Out of the switch, I only have about 8 lbs. Is this normal? Do I have a defective switch or is something else wrong?

By the way, it's a 94 F150.

 

check vacuum on the blend door side. it sounds like a vacuum leak somewhere and its not allowing it to shift to any other position

 

I had this same problem. Theres a vac can on the side of the A/C box thats glued on from the factory. The glue gets week and starts to leak and needs to be resealed. Matt