Thanks for all the responses and help on this. I finally tracked down and fixed the problem. I pulled the ACC unit and the panel of switches on the console above it. I found an electrical connection had been pulled off of the center vent vacuum swtchover valve. Put it back on and all is well in the vacuum system. Car shuts off-center vents work and door locks etc. all functioning now.

Amazing how one little electrical connection can throw this whole car out of whack. As I get a deeper understanding of the vacuum system and get better at troubleshooting it, I find myself growing fonder and fonder of these little beasts.

Again thanks to everyone for the help.

__________________
- Matt

1978 300SD China Blue 178k
1982 300TD Manila Beige 120k
1982 300D Manila Beige 192k
1984 300SD Needs Paint 240k