My 1994 965's front vents close up only during medium to hard acceleration and on long hills, and switch to simultaneous defrost and floor vents. Slow acceleration has no adverse effects. This is a big problem in Las Vegas when it's around 110 degrees. I removed the lower panels to access vacuum motors and while idling, removed one by one, vacuum hoses to each one. The single vacuum motor behind, not above, the double acting vacuum motor produces the same symptom when disconnected. The double acting motor seems to have no effect on the front vents when disconnected. The single one on top, when disconnected, only reduces the air flow to the front vents by about half.
I have read all the posts that I could find and am still confused about which vacuum motor might be the culprit. Some have pointed out the double acting vacuum motor, while others have mentioned recirc vacuum motor. Does anyone have experience fixing this? Would I be better off just replacing all the vacuum motors in one shot(little over $50.00 each)?
Any help will be greatly appreciated.