Yes, the vacuum switch (I guess you would call it) at the control panel will sometimes develop a leak or break and will not pull the associated vacuum actuators to close and open the correct doors. Also, sometimes one of the vacuum hoses that go from the switch to the actuators get torn or pulled off and the same thing will happen.
First thing I would do is check all the vacuum lines from the canister under the hood all the way to the switch and from the switch to the vacuum actuators. Check the vacuum control actuators at the heater box to see if they hold vacuum. Then pull the heater/AC control panel and check the switch.
The switch in my truck doesn't work right either. I keep telling myself that I'm going to replace it, but I never do.
Hope this helps,
P.S. You don't have to shout (all caps), we can hear you just fine.
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Mike
1985 Chevy C-10
Mike's 73-87 Chevy Pickup Site
[This message has been edited by swervin ervin (edited 12-06-2000).]