Ok, i just had to drive back to Florida and home again last week. On the way back, i noticed when i would accelerate, the a/c would start blowing out of the defrost only, not the vents. Did this on MAX a/c and the regular setting. The truck is a Lariat and has the automatic a/c controls, not the *****. I thought i remember reading about some small o-rings located inside the control unit that go bad and can be replaced for a few doallars and time. Anyone know anything about that, or am i having another flashback?

Thanks!

 

Vacuum leak, either in the supply line from the engine compartment or the o'rings in the vacuum solenoids in the control head.

 

Where are the vacuum lines in the engine compartment? I have not had a chance to look too close yet. It seems to work fine around town yesterday and today.. kind of an intermittent thing. Where can you buy the control units? I looked on RockAuto yesterday just to get an idea if i can't fix it by replacing o-rings, didn't see anything. Thanks for the response, projectSHO89.

 

I had the same problem with my 93 F-150, it was the vac valve that controls the defrost flapper door. There is a hard plastic vac line that plugs into the vac valve; it was dry rotten/ cracked near the valve. I bought a 1 foot long piece of vac hose (.75 cents) to replace the length I cut off. Problem fixed. The vac valve on my 93 was on the fire wall on pass side. Hope this helps