A/C system?

[deputydawg]

When I accelerate the vents shift from the dash to the floor, once the RMS level out- the air blows through the dash vents again. Is this a vacuum issue? If so, how do I fix it? I notice if I get on it, it sounds like a duct is opening and closing on the left front side of the car....any clues?

[JHensberry]

If I am not mistaken, someone please correct me if I am wrong, but that is normal operation. I know mine used to do that when the A/C worked. The little black plastic ball thingy helps regulate the engine vacuum when under a load.

[deputydawg]

is that bulb thingy what is making the thud noise? maybe I should replace it.

[Keller]

No...The air path should not change under boost. There may be a bad check valve in the system somewhere.