This sounds like the actuator that is not moving and allowing airflow to the defroster.
I attached the procedure and location for you of the actuator for this control.
These actuators are very common failures for airflow directions.
Front Mode Control Motor Replacement
1. Disconnect the 7P connector (A) from the front mode control motor (B). Remove the rods (C) of the front mode control motor from the front mode control motor linkage (D) and the front mode control linkage (E). Remove the self-tapping screws and the front mode control motor from the heater unit.
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2. Install the motor in the reverse order of removal. After installation, make sure the motor runs smoothly.
Thursday, November 12th, 2020 AT 1:55 AM