When I shut off the van(A/C running) there is a groan that sounds like someone letting air out of a balloon,while pinching the outlet. the engine is not running hot and the A/C is cooling.The sound is coming from the front and seems to be cooling/heating related. can anyone help?
Thanks Bob

It sounds like a kid making the annoying, high pitched screaching sound from a balloon with its opening pinched and stretched flat? Are you having any trouble getting the air to blow from the dash vent or is it always coming from the defrost? You should run the car parked and stick your head under the dash and glove box to listen for any sounds, hissing, sucking. Everything you have described fits with the vaccuum operated hvac system. Was this noise heard inside? I know my van will make various moving and groaning noises when turning it off and having the ac on. It sounds you have something additional like a line or motor/accuator or control panel leak caused by failure or disconnection. It sounds like a line may only be a little loose so when vacuum is drawn, it sucks closed, and when the vacuum goes away when you turn it off, the vacuum is not strong enough to hold it together and that's the squeeling, screeching sound you hear. If not inside, the problem could be just on the other side of the firewall where the vac lines connect to a vac reservoir. has any work been done recently on the van? Bottom line, this clearly sounds vacuum related.

Thanks for the info,you know what I'm talking about.Now that I think about it,there does not seem to be as much air blowing out of the vents as in the past.how do I get to the line that operates the air flow to the dash vents.
Thanks Bob

I had the same sound on my windstar (may it rest in peace) and it drove me nuts for a couple of weeks. Starts to whine about 20 to 30 seconds after shut off and continues for about 10 to 15 seconds. Such a noise that my dogs would start howling with it. I found that the vent line to the front valve cover (3/8" fuel line) had softened with age enough that it was "sucking" closed while the engine was running. after turn off it would start to open, releasing vacuum and sounding like a balloon squealing.......replaced the hose, things were quiet again.

I liked my windstar, but just 2 weeks ago it met it's end on US 290 in Austin, TX. It will donate many parts to keep others alive.