MIX-BLEND Mode
WARNING: This page is about a different car, the 2002 GMC Safari and 2002 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.
When the operator selects MIX-BLEND, the following occurs: The mode actuator has vacuum applied to it through the Red vacuum line, pushing the vent door closed. Vacuum is bled off the defrost actuator, holding the defrost door stationary in the half-open position. The heater door is also held stationary in the half-open position through mechanical linkage.