Thanks Michael!

 

Same problem here. A/C was switching to defrost while the Schurshun was under load pulling a hill, etc. Turned out to be bad check valve in the vacuum reservoir. Changed out reservoir and all okay. Inexpensive part at Ford.

 

AC/DC WELCOME to the world where everything is XXX
Please add your general local to your profile so's wese nos abouts where U's is

 

[QUOTE=ChadTaylor;15418693]Hey Folks!

The wife and I went out for lunch yesterday and I ran into some odd stuff with my A/C on the way home.
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This can also be caused by not running inner fenders and your vacuum canister falling out. Make sure that the canister is still intact!

 

Found my vacuum leak today, vent positions now work perfectly.... I replaced the pump a couple of weeks ago, no change. I had chassed all vacuum lines and everything looked good. When ever I got onto the skinny peddle on the right the defrosters would come on. So every time I had the hood open I looked at vacuum lines, nothing....



Today I took the vacuum tank out ( 3 nuts under the fender well ) and all of a sudden I found the break.... The numb N&ts previous owner had found the break too... He just slid the to broken ends of the line into a piece of rubber vacuum hose and didn't bother to seal it.... Thanks everyone for keep telling me it was a vacuum leak.... IT WAS

 

Glad you found it and it was a simple fix, but now you have me confused a little.
You said that you replaced the vacuum pump, so that means a deezle right? If so I don't understand why the HVAC would default to the defrost position only when you leaned into the skinny pedal, deezles don't generate vacuum (that's why you have a vacuum pump) so how does the skinny pedal affect the HVAC? On a gasser it would make sense as the vacuum generated by the motor drops off some at higher throttle openings, which would have the HVAC going to the default defrost position.
Am I missing something obvious here?

 

Which fuse?

 

That line/valve controls the coolant shutoff for the heater core. It operates on vacuum but only when the selector switch is in the MAX position. It makes the system more efficient by minimizing the heat getting into the interior air flow.
The system defaults (no vacuum) to open so you will have heat if it malfunctions. Same thing as defaulting to the defroster vents. Gotta keep the windshield clear.
So if you only experience the problem when running on MAX, this is the first place to look.