All valves (except the temp control door) are controlled by vacuum motors. If I remeber right there are two on the heater box and one on the kick panel, oh yea and the one inside the cowl. It should be the motor that is on the back side of the heater box, between the box and the firewall. It should direct the airflow out to the dash vents (center and both eyeballs.)
I'll try to find that diagram of the lines, but it may take me a while.