Your vents are run by vacuum supplied by the engine. There's a small rubber hose from intake manifold to the firewall under the hood, somewhere on the right (passenger) side of the engine compartment. It may be split, cut, or fell off. It probably connects at or near a check valve, a little plastic disc on a bigger vacuum line. The one you're looking for is small, 1/4 inch or less in size.

Without vacuum, the vents run only in a default mode, and that sounds like what you have. The back of the vent controls is a big connection for about 10 little vacuum hoses; practically everything in the system besides the blower motor is controlled by vacuum.

Good luck with it!
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Rob Bareiss, New London CT ::: Roterande Fläkt Och Drivremmar!