Air conditioning venting problem

[stevo9029]

While driving and the A/c is on recirculate the air vents change and goes to the floor panels when i hit the gas.... Does anyone know why it does this and/or what needs to replaced on it?

[nechi20]

the mode doors are pulled by vacuum from the engine. theres a check valve inline, it's supposed to be designed to let air flow one way only, like a diode. this is to hold in the vacuum, in the event you lose vacuum.. (IE: boost!) so when you hit the gas, the boost is pushing the mode doors back! The connection for this is on top your brake booster.. follow the small line, and you'll find it.. its either missing, or shot!

[charger R/T]

The above info is correct but to add to it. Most of these 4 cylinder cars cruise at a lower vacuum reading them a v6 or v8 would. The dash needs a certain level of vacuum to work correct. If you are cruising at a vacuum reading at or lower then this magic number and have a small vacuum leak in the dash the vents will switch on there own eventually. So a new check valve may fix the car if it is the issue but if it is not it won't. If it switches as you romp on it it could be just a check valve but if a new one does not fix it it could have a vacuum leak big enough to use all the vacuum right away. get a helper and put a piece of rubber hose at the check valve and start the engine put it in the mode it switches and pinch the hose closed with some pliers if it stays blowing out the A/C vents a new check valve may fix it. If it switches right away you have a vacuum leak. Vacuum leaks usually do not make a noise you can hear. It would have to be a big vacuum leak to hear. I don't think the small tubing used in the dash is big enough to hear.
Tim