My Bonneville has done this since the first day I've owned it. I thought maybe by replacing all the vaccum motors and everything while I was behind the dash fixing the heat actuator anyways, that maybe that would fix it, but it didnt :(

Anyways, does anyone else have a problem, or notice that if you have your A/C, or even just regular vent on, and you having the air coming out of the front vents, when you put your foot down to climb a hill or to accelerate fast (like to pass someone or to merge onto the highway), that for some reason the air stops blowing out of the front vents and starts blowing out of the defrost / floor vents until you let up??

Maybe my car just has some serious climate control issues, but I figured it would be worth a shot to see if this happens to anyone else too, and if anyone has found a fix for it. :?: It'* almost like the engine switches the vents when its under load, or needs power, and then switches everything back once you take your foot off the gas, or let up on it.

Wierd! :( Thanks for the info in Advance!!

Maybe it has something to do with the AC compressor clutch disengaging at WOT?

Check the vacuum hose on the firewall to a triangular shaped black box next to the plastic panel that covers the relays. It'* located on the driver'* side of the car. This box controls the vacuum vent doors. I've had a loose & damaged hose before which caused the doors not switch back & forth.

Dont think its the A/c compressor clutch, because it does it with just the outside air vetn on and the A/C off too...

I'll have to check that vacuum box. Thats what I was kinda thinking it was, was something to do with Vacuum. I know that all of the valves behind the dash are ok, because they are ALL brand new, I replaced them when I had the dashboard out. It was doing this both before and after I did the dash job so I know its nothing I caused. Its actually done this since the day I bought it :( It'* not bad, but it gets annyoing real quick especially on nice hot days when your being blessed with full A/C, and then all the sudden you go up a hill and it switches to putting it out the defrost and floor. Without that cool air blowing, you get hot again real quick, then it comes back once you let up on the gas. Another hill, does the same thing, etc.....

Any more suggestions ?

The only other thing I can think of is a loose or missed connection when you put the dash back together? you can check for a vacuum leak under the hood with a spray nozzle & some water. You can check the valves for the doors while someone is switching the controls back & forth too. Find out exactly which door is NOT working properly first, then trace back the vacuum lines.

It has been doing this for almost 3 years since I bought it, I just did the dash 2 weeks ago so I've definetely ruled that out. Theres really not that much to hook / unhook back there at all really. All of the climate control stuff like the air dist. box, etc all stays bolted to the firewall, the only thing you need to uinhook when pulling the entire dash like I did is 1 BIG wiring harness block, and a 2-3 other little 2-3 Pin wire connectors. Everything else thats vacuum and whatnot stays on the car. Its actually pretty simple...

Hey Chris I'm having a similar problem...I can't get the doors to switch off of the defrost at all. I've been so busy lately I haven't had a chance to really check anything out, but tomorrow I'll have to start with that vacuum box. I just hope it'* something simple.

when you accelerate hard the vacuum in the motor drops to almost nothing. the CC system then loses all its vacuum, eventually, so the flaps default back to defrost. once you get a decent amount of vacuum back the flaps go back to where the should be.


this kind of problem always happens to me in the winter when i first start up the car... seems moisture or something gets in the vacuum lines, freezes, and prevents the flaps from moving anywhere until things get cooking.

Is there a way to prevent this, or fix it from happening? It is the ONLY problem with my car right now, and it is really annoying. The rest of the car is flawless. I just dont understand why noone elses does this under acceleration, and mine does? If your right, and under heavy accel (passing, climbing hills, etc..) the vacuum in the motor drops, which is possibly causing my problems, why doesnt it happen to anyone else? I'm not trying to say your wrong, because I think your right on track, it seems like somethings loosing vacuum, now I just need to figure out why, and where its going

I know its not related to the cliamte control alone, because pretty much every single climate control part in my car has been replacded, from the HVAC Programmer and digital display, right down to the vent doors and motors.

Anyone know where I should look, or what I should do to test for a problem like this?

Thanks as always!!

Anyone have any progress to report....I have a 96 SE Bonne, and mine started doing the vent change routine a few months back, a friend of mine has a Lumina that is now doing the same thing....it must be a major flaw with GM a/c

Help anyone??? Thanks, Dylansdad