Is the heater / AC blend door activated by electric or vacuum on this model? Where is the actuator located?

My auto climate control system seems to have gone south because it's stuck in AC mode. I've got hot coolant flowing thru the heater core at fire hose volume. The dash control unit is OK, it tests as new. All vacuum lines and wiring in place and OK. I'm at a loss as to where the unit is. I sure can use some help with this. Winter can be brutal here in western New York. I'm going to need a good working heater!