problems with the climate control switches. on 2004 Jeep Grand Cherokee

when the knobs are turned to select either defrost or floor heat the unit does not switch. does this mean the unit is bad or should I start with a disconnected air duct or what?

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2 answers
Could be a number of things. Most likely would be the mode door actuator. A good repair shop should be able diagnose this for you.
do not guess,have a diag done to make sure