Don't know much about the '94 HVAC system but looking at the AC schematic it looks like your Panel Door actuator has failed in the closed position. Lack of vacuum to the actuator to operate it (Should be open in all phases of AC operation, except Heat and Defrost) may be the AC Control Unit or lack of vacuum to the Control Unit, i.e., canister (Reservoir) broken, or vacuum lines to and/or from the canister to the Control Unit loose or broken, or the actuator itself has failed.
If you have a hand held vacuum pump you could go to the intake manifold and try vacuuming down the tube that goes to the canister and see if it holds. If not go to the canister, remove the tube going to the firewall (to the Control Unit) and apply vacuum to it and see if it holds. If it does, the canister is bad perhaps. If it does not hold, it could be a bad AC Control Unit, or the hose(s) at the back of the control unit are leaking. See if you can isolate the leak (if any).
