I posted this question some time back but lost the replies. Please forgive the duplicate request.
I have a '93 full-size Bronco. I have a problem with the dash vents. While accelerating and therefore depleting my vacuum reserve, my A/C defaults to blowing through the defrost vents. When I decelerate, the vacuum recovers and my A/C goes back to blowing as it should, through the dash vents.
Anyone have any advise as to where to look first for the leak. I've already replaced a small vacuum valve/device under the hood to no avail.
Thank you NES