I hope you can help.
I have a 1997 Expy with 5.4L engine.
When I switch on the A/c on it blows fine, nice and cold. However, when I apply the throttle moderately, the panels shut off, and the defroster vents start to blow regular air.
The panels and a/c only come back on if I let off of the gas.
Any help appreciated.
Thanks!!!

 

You have a vacuum leak. If you do a forums search will find about 100 threads on it.

 

I had the same problem. When accelerating lightly the airflow would shift to the defroster vents, once one let off the throttle the air would once again flow out of the panel registers. This is indicative of a vacuum leak. In my case it was the vacuum motor for the defrost diverter door. The vacuum motor in question is located just above and to the right of the gas pedal. Its not to difficult to get at or replace.

- Push seat back all the way
- Lay down on floor boards looking up at gas pedal.
- Behind and to the right of gas pedal you will find a black cylindrical housing.
- Remove vacuum plug from vacuum motor. (Dual lines on back side)
- Remove one hold down screw.
- Vacuum motor working end has a metal hook which slides thru the eyelet on the defrost diverter door. Wiggle and hook will disengage and vacuum motor can be removed.
- To reinstall, reverse the order. Be advised that the diverter door is hinged and spring loaded and will probably pop up making it difficult to install the hook into the eyelet. To overcome this problem, start engine, turn on blower fan and using a wire or needle nose pliers, pull defrost diverter door down. Once down the fan air pressure will hold it closed so one can install hook into eyelet.
- Vacuum motor is $18.00 at your local Ford stealer.

Good luck

Cheers; JOE


Good luck!