Volvo S90 2019 Owner's Manual page 210

CLIMATE
Table of air distribution options
The air distribution can be changed manually
if required. The following options are available
for setting.
Air distribution
If all air distribution buttons are deselected in manual mode, the climate control system returns to automatically regulated climate
control.
Main air flow from the defroster vents. Some air flows from other air
vents.
Main air flow from the air vents in the instrument panel. Some air flows
from other air vents.
Main air flow from the air vents at the floor. Some air flows from other
air vents.
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Purpose
Counteracts misting and icing in a cold and humid cli-
mate (to achieve this, fan level must not be low).
Provides efficient cooling in a hot climate.
Provides heat or cooling to the floor.