Hey, did you ever get this fixed? I am working on mine again.
The switchover valve is to the left of the glove box, and down. Remove the glove box liner and you can see it; it will be several inches in length vertically and have a bunch of vacuum lines attached to sither side. it looks sort of like a vacuum version of a wiring terminal strip. this controls the vacuum flow to the different pods, to make the air come out of the different vents. if you remove he knee bolster (carpeted part underneath the dash on passenger's side) you can get better access.
Since I can't get heat to come out of the floor vents, only the defroster and side vents, I know I either have a bad vacuum pod or a problem with the switchover. gotta tear into it. My switchover has been clicking repeatedly on cold start; if I go a few miles down the road before I turn on the climate control, no clicking. Hummmn.....