We have a problem with our 96 Bonneville. We cannot change the vents for the heat/AC. It is not in the controller, I replaced it recently and everything else works. When you push the Mode buttone it does not switch the air outlets. It is always on the split defrost/floor setting no matter what the control panel indicates. Any ideas on how to repair this?

Have you checked the vacuums lines for leaks?

No I haven't, I'll have to see what I can find. Is that how the vents change?

I have the same problem with my 96. The electronic temp units require a "ac controller" unit to change to fresh air or heated air and the defrost to floorsettings. This drove me crazy! At first I even bypassed the heater core during the summer because the door was stuck on heated air. It Sucked, I'm still looking for a used controller for this car. I've been quoted $700. for a new one! Still looking!