You've got a bit of work ahead of you.

The best thing is to access the switchover valves which sit in a row next to the climate control unit on the right side. You'll need to remove the carpeting and kick panel on the right side and then carefully remove the carpeted transmission tunnel piece to access them.

The horizontal port from each valve goes to one..........or more than one........of the vacuum pods that operate the doors. You'll need to check each horizontal port with a Mityvac and see if they hold vacuum. The tests that don't hold vacuum indicate a pod that needs replacement.

If you get the tests done and provide the results for which pods don't hold vacuum, we can guide you to where they are located. Usually, it's the dual pods for the main door and the defrost that fail and leak vacuum. The entire system doesn't function until the leaks are corrected.