Hi Gang,

My AC flow is being directed probably 75% through the defroster vents, and the rest through the dash vents. This is no matter which setting I have the control set to. I understand there is a door inside the ducts that directs the air flow to the proper place. Is this door prone to getting stuck? Is it vacuum or electrically or mechanically controlled? Or, is it possible the control itself is the problem? BTW, if it makes any difference, my stereo was stolen the other day, but it looked like a "clean" heist...no other damage, except for the cracked trim. I put my stock AM/FM back in - it plugged right in. Could the thief who ripped me off disconnected something?

Also, my Bonne just has the basic AC controls.

I appreciate the help.

Thanks,
NCC

Sounds like one of the little 1/8 inch diameter tubes to the vacuum motors got disconnected. I spent lots of closeup time with my 98 vacuum setup but it'* the computer controlled type.

I suspect the tube for the valve that closes off the defroster duct and makes the air come out the dash instead of defrost is off or the vacuum motor has been damaged or loosened in some way.

Do you hear the motors move when you select heat and bilevel and each of the other settings? Run the car for a second to build vacuum and then quickly punch through those buttons. If yyou hear the movement, that means you're getting vacuum.

Thanks for the reply.

I will check closer, but I was listening for the opening/cloing sound of that door, and I havent heard a thing. If I wanted to track down a loose or damaged vacuum line, where should I start? I know there are several on the other side of the firewall, but I suspect that "door" is behind the radio/climate controls somewhere. This vacuum motor, where is it located?

Thanks for the response!
NCC

This is a thread with a similar problem. It should answer most, if not all of your questions.

http://www.bonnevilleclub.com/forum/...ic.php?t=59735

Thanks for the replies. They are helping.

And now for more info. I checked for the sound of the door closing/opening...nothing. As noted above, my Pioneer HU was stolen out of my car. Temporarily, I replaced it with my OEM AM/FM/ Cass stereo. Basically, the unit slides in on a center track, like a drawer in a dresser. When I removed it this afternoon to look around, the AC was redirected out the dash vents, and stopped coming out the defroster. Not so fast! Now, I don't get anything out of the defroster, even when it'* set to defrost. So, I helped one problem while creating another. What'* the common thread between these 2 issues? I cant see anything behind the stereo that would cause the original problem to happen (like something crimped or disconnected). Any more thoughts/suggestions?

I will look into the vacuum hose as suggested in the linked post.

Thanks again!
NCC

Does the control change things like heat and bilevel settings? Do you hear motors moving there like I described earlier?

Did you mean that when you pulled the stereo out the dash vents started working and the defrost won't or is it just that now it'* working that way? If so the second could mean a valve or motor that'* sticking. The hose to the vacuum motor will be blue. There are three vacuum motors. The motor to the left facing down is the recirculate, the one to front is heater, ac, bilevel, and the one upmost of the three with the connection for vacuum on top is the defrost ac valve. You might try pushing in on the diaphragm. the diaphragm has a spring that makes it go to defrost setting unless there'* vacuum pulling it in and then the valve inside the heater box is moved to dash vents and the defrost blocked.

A quick check once you get to the blue valve is run car motor briefly and put damp fingertip over end of vacuum hose; the vacuum will stick to your finger when you select AC setting; no vacuum when you select defrost. If no vacuum in either setting, then you have vacuum loss somewhere else along the line.


To see these, you take off the hush panel under the passenger dash. I don't believe I had to take off the hush panel on the driver'* side.

I'm working from a Buick manual for 93; but the Bonneville should be the same heater box.