Why is there constant vacuum to heater control valve ?

[Burnsy]

With the truck shut down, key out, im able to release the vac by turning the ac controls dial to reg ac......i know there isn't supposed to be vac in reg ac but is the dial supposed to be sending a signal when the truck is off no key in ignition etc ?

 

[RonD]

Vacuum valve control is not electrical so key on or off doesn't matter
The selector on the dash has the 5 hoses hooked to it and sends vacuum to the "motors" when ever you change positions

Vacuum hose diagram here: https://www.ford-trucks.com/forums/attachment.php?attachmentid=517&stc=1

5 hoses attached to the back of the selector, the selector connects any of the 4 hoses to the Black hose(reservoir) to give vacuum to that hose
As long as reservoir has vacuum then that vacuum "motor" will respond by changing vent position
Nothing electric required

On the right is the "grey" hose in engine bay, "T'ed" off the white hose in the cab

When in OFF position the Yellow, Blue and White(and grey) have vacuum because they are connected to the Black hose

 

[Burnsy]

Vacuum valve control is not electrical so key on or off doesn't matter
The selector on the dash has the 5 hoses hooked to it and sends vacuum to the "motors" when ever you change positions

Vacuum hose diagram here: https://www.ford-trucks.com/forums/attachment.php?attachmentid=517&stc=1

5 hoses attached to the back of the selector, the selector connects any of the 4 hoses to the Black hose(reservoir) to give vacuum to that hose
As long as reservoir has vacuum then that vacuum "motor" will respond by changing vent position
Nothing electric required

On the right is the "grey" hose in engine bay, "T'ed" off the white hose in the cab

When in OFF position the Yellow, Blue and White(and grey) have vacuum because they are connected to the Black hose

Thanks !!