Volvo FM Handbook page 331

320 Cab
Air distribution
Always leave the panel nozzles (1) open. Irrespective
of how the air distribution is set, a small amount of air
will always come from the panel nozzles to ensure that
the temperature distribution in the cab is correct.
1 Panel
2 Floor
3 Defrost
The normal air distribution provides slightly warmer
air to the feet and cooler air to the head. This is to
create a good working environment for the driver.
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