Vacuum problem

[vl1500]

While driving with the a/c on the air blows through the vents until I reach a certain speed and then it starts blowing through the defrost and floor vents any suggestions? Thanks.

 

[scot w.]

While driving with the a/c on the air blows through the vents until I reach a certain speed and then it starts blowing through the defrost and floor vents any suggestions? Thanks.

First! check the checkvalve in the vacume line by the drivers side valve cover. make SHURE it only sucks in one direction (towards the front of the car) it's not supposed to blow towards the fire wall AT ALL! if that is bad replace it your getting boost into your a/c and heat lines. if it's good work your way to the one that is on the drivers side firewall by the valvecover with two lines coming out the top. and see if it is any good. just kinda work your way from the first checkvalve to the firewall and then into the car. my quess is when your car gets into boost it's making you loose your vacume. >> bad checkvalve somewhere!! I just went through this myself but my a/c would'nt even blow out the vent's at all. checkvalve was reversed good luck! let us know if this works, scot w.

 

[scottyb]

Are you sure it's speed related? Adding to what Scot said, it's more likely "power setting" related - as in the more pedal you give it, the lower the vacuum - then no source of vacuum under boost. If you maintain say 50 mph, do the vents open back up?

Follow from the check valve Scot mentioned and search for vac leaks. That vacuum "circuit" is shared with the cruise control and the EGR. Maybe you should cap those off one by one so you can run a process of elimination.

There's also a vacuum "stoarge ball" behind the driver headlight that is meant to maintain vacuum during the short periods of boost (or low vacuum).