Hi everyone ill try to make it short . Ive noticed when driving once i hit about 50mph or when i push down gaspedal hard i start getting hot air coming from the vents and the defrost vents even when i have the system off. but when i let off the gas it seems to stop . it seems like some door is opening letting the hot air come in ? One problem im fixing is the parking brake release valve it looks like a lil half moon under the dash board drivers side its hissing does anyone think that the leak from the pbrv is screwing up the whole vacum of the car because when i step on the gas the hissing goes away from that valve please help sorry i tried to make it short thank you car has 72000 miles

One way to find out.. pull the line off the pbrv and plug the line while your looking for a new valve.

Seems to me though, that tiny line wouldn't be enough to draw from the rest of the system enough to cause the plenum doors to move.

I would check the larger hoses connected to the intake manifold too.. power brake booster etc.

Hey steve thanks ill look around at all the lines i was just hoping it was the relese valve but one thing i did change was the some auto temp control valve it works on vacum also i wasnt getting any ac now with new one in its blasting cold air maybe that worked have to take it for a good run see if i get the hot air still blowing but my luck its never that easy lol thanks

Check this post too:
http://www.lincolnsonline.com/forum/showthread.php?t=64362