I recently discovered that the heater and air conditioner controls on my 1978 F250 have stopped working. I think they are all actuated by vacuum because I no longer here the sucking and clicking noises when I change from heat to defrost Etc. The air only comes out of the defrost vents regardless of the setting. I cannot hear any vacuum leak that would indicate a broken line or anything. My Haynes manual doesn,t have any clues. Any help you guys could give me would be appreciated!

Bill

 

On my 77 400ci there is a vacuum "manifold" on the rear pasenger side of the intake manifold. It's an aluminum thingie that has a large outlet for the power brake booster and several smaller take offs for the tranny modulator etc. and one that goes in the dash and powers your heater selector. Sounds like it's off or leaking badly.

1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything

 

Mine runs from the intake to a 'coffee can' reserve and then into the cab thru the fire wall. I then goes to the back of the control, and a whole bunch of control lines from there. I'd check for vac leaks.

 

Oh yeah, mine has a plastic ball vauum resevoir. The nipple for the hose broke off of it once, same effect1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything

 

Thank you all for the help. I finally got a chance to look at the problem this weekend abd found that the vacuun line from the intake manifold to the heater controls was disconnected. I think when I had the motor worked on last time, the hose was left off because there was not enough vacuum nipples on the intake manifold. What probably happened is that the mechanic hooked the heated air diverter in the air cleaner assembly to the nipple that had been connected to the heater controls, and that before he started the air diverter was the line that wasn't connected, and I never noticed that the heated air system wasn't working before. I bought a tee and connected them both to the same port on the manifold. Thanks again for your help!