Vents problem

[xTOM153x]

For some reason whenever I have the A/C on it will blow out the front vents for a while but after about 2-3 min it will stop blowing air out the front vents and just start blowing air out the top almost like its changing it by itself. Anyone have this problem before?

 

[stangcbr]

I am having a similar problem. The vents will change by themselves even with the front vents selected. I think there is a vacuum problem somewhere since vacuum controls that stuff. I am getting a vacuum guage from work to see if I can figure out the problem. Did you ever get this figured out? I also had a sucking sound coming out of my passenger side a soon as I lightly pressed the throttle. I determined this was coming from the vacuum vessel (black plastic resevoir that sits under teh passenger dash and saves vacuum if the engine drops its supply such as while accelerating).

 

[Gus Gorilla]

Gentlemen, I have an answer. Stangcbr (car/bike?) is correct. Most likely this is a vacuum leak or failure. The failsafe is to default to Defrost. (it keeps the windshield clear for visibility safety). If you have a vacuum leak then going to Wide Open Throttle WOT will drop all vacuum and the system goes to defrost. This can be something as simple as a leaky vacuum line or as severe as an exhaust restriction. I had my Y-pipe cats fail and cause a very similar problem.