It sounds like the mode blend door actuator is not working, or the control cable is disconnected. Here is a diagrams below to show you what to look for.
Cheers, Ken
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Dec 8, 2018 at 12:57 PM
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.