Mercedes-Benz 2016 GL Operator's Manual page 164

Setting the air vents
162
B-pillar air vent in the headliner
B-pillar air vent
:
Thumbwheel for B-pillar air vent
;
To open or close: turn thumbwheel ; up
X
or down.
Third row of seats
B-pillar air vent in the headliner
B-pillar air vent
:
Thumbwheel for B-pillar air vent
;
To open or close: turn thumbwheel ; up
X
or down.