Air flow is stuck blowing out vents and it won't turn

Oops. You may need to buy that switch first. Then you need to figure out why the airflow isn't being directed to the defroster vents. With the engine running, move the control between the different settings and listen for the actuators and doors moving. Check wiring and any vacuum connections to the airbox and blend door assemblies. Make sure if there are cables to the actuator(s), they move freely. Disconnect them and move the actuators by hand and see if they move easily farther than with the control.