Floor Mode
WARNING: This page is about a different car, the 2002 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.
When the operator selects FLOOR, the mode actuator has vacuum applied to it through the Red vacuum line, pushing the vent door closed. The defrost actuator has vacuum applied to it through the Green vacuum line, pulling the defrost door closed and opening the heater door through mechanical linkage.