Hyundai NEXO 2019 Owner's Manual page 269

WARNING
Keep the air intakes clear.
To assure proper operation of the ventilation system, keep the ventilation air intakes located in front of the wind-
shield clear of snow, ice, leaves, or other obstructions.
If you must drive with the liftgate open:
Close all windows.
Open instrument panel air vents.
Set the air intake control at "Fresh", the air flow control at "Floor" or "Face", and the fan control set to high.
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