Floor Mode
WARNING: This page is about a different car, the 2003 GMC Safari and 2003 Chevrolet Astro. 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 Brown vacuum line, pushing the vent door closed. The defrost actuator has vacuum applied to it through the Blue vacuum line, pulling the defrost door closed and opening the heater door through mechanical linkage.