Originally Posted by pdieni
Where is this valve ? Passenger area or in engine bay ?
In addition to what Bluewater1 did here
, in your case, I would also replace the Heater Control Valve (which is in the engine compartment, on one of the heater hoses/lines). These valves are cheap: $ 15-18 shipped.
When you check the Vacuum Controller, check the vacuum lines for cracks. Check also the vacuum reservoir for cracks.