Acura MDX Owner's Manual page 191

uuClimate Control SystemuUsing Automatic Climate Control
■
Switching between the recirculation and fresh air modes
190
1. Select or currently shown.
2. Switch the mode depending on
environmental conditions to the following:
(Recirculation Mode): Recirculates air
from the vehicle's interior through the system.
(Fresh Air Mode): Maintains outside
ventilation. Keep the system in fresh air mode
in normal situations.