When I am going up a hill with AC operating, cool air stops coming from the AC outlets and comes from the outlets up under the front window. If I let off the accelerator the air shifts back to the AC outlets. This seems like some type of vac loss that results in one of the vent valves shifting from cooling postion to heat position. Any idea where to begin. This is a 1997 Ford F250 super duty with big 8 cyclinder engine. Side note is that I have a 1989 F350 that does the same thing.

 

Yup -sounds like a vacuum issue.

Which Engine - PSD or Gas V8?

If it's a PSD I'd be looking @ the vacuum pump.

DG

 

This vehicle is a gas gussler....460

 

Are the valves that open/close the doors in the AC./Heater operated off voltage or vacumn?

 

Controls are all vacuum. Only Electrical controls are for the fan/blower.

DG

 

We notice when we leave AC using outside air that valve that determines whether air goes thru the AC vents or the defroster vents works properly. When in max AC we get the failure when vac pulls down. When using max air are two vac valves operated at the same time.