On my 1994 Supercab when I turn the vent control **** from AC to Max AC at driving speeds the air flow stops, at idle the air flows. When I turn it back to AC the air flows returns to normal. Any ideas on what to check?
Roger

 

You are losing vacuum. When the air "leaves", check the defrost vent. If the air is coming out of there, you are losing vacuum. First place to look is at the pass rear of the engine compartment. There is a white vacuum line going to a vacuum motor on top of the ductwork. This line will deteriorate and cause vacuum leaks. Just cut it back to a good part and replace with the small vacuum hose that you can get from Advance. Should solve your problem.


Robbie