Sounds to me like you have a problem with the vacuum system that controls the the air doors inside the dashboard. Have you run the self-diagnostic on the A/C system yet? What did it say? The procedure is here if you need it.

Also, if you haven't done so already, get a copy of WIS or a subscription to alldatadiy.com. There's lots of good info the be had there!

__________________
"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles