Hello Ruckus.
There is a vacuum controlled actuator on the heater box to the right of the drivers foot.
You may need to remove a hush panel to see it.
The vacuum line may be cracked or broken to this.
Or the mechanical connection to the door may have fallen off.
If it appears to be intact check for vacuum at the line when you move the control.
Here is a diagram to help you locate it. The actuators are on the left side of the diagram.
Thank you for using FixYa.
KL