Hissing when climate control is set to 'Off'

[PashRoot]

So apparently I've got yet another vacuum leak to hunt down, although it isn't a critical one either. Engine still runs smoothly. At worst I'm probably wasting more gas.

If I switch the climate control to any other setting besides off, the hissing disappears. When I shut off the engine, the hissing continues for a good 10-20 seconds before fading away.

Which vacuum line or 'reservoir' controls the 'off' position?

97 Ford Explorer OHV RWD

 

[koda2000]

the EATC controls work on vacuum and electronic solenoids. i suggest you remove the EATC module (pretty easy to do) and see where the leak is. it could be a hose or a solenoid o-ring.