Mazda CX-9 2018 Owner's Manual page 346

Interior Features
Climate Control System
Vent Operation (Rear)
▼ Adjusting the Vents
Directing airflow
You can direct air flow by moving the adjustment knob.
NOTE
When using the air conditioner, mist may come out from the vents. This is not a sign of
trouble but a result of humid air being suddenly cooled.
knob
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CX-9_8GC3-EA-17G_Edition1 2017-5-29 10:13:38