The airflow direction is controlled by the mode door actuator. On this vehicle, it is actuated by an engine vacuum.
When you switch from floor to defrost, does the air flow change direction?
I attached a vacuum schematic below and highlighted the actuator in question. Let me know if you can control the other airflow directions so I know which way to go.
Also, with the engine running, pay attention for any air sounds or hissing sounds when you select the vent doors.
Take care,
Joe
See pic below.
Image (Click to make bigger)
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Wednesday, September 21st, 2022 AT 5:48 PM