Tesla S Owner's Manual page 121

Climate Controls
6. Choose how air is drawn into Model S:
7. Touch AUTO to change all settings back to their default values. The icon is blue whenever the
climate control system is set to AUTO.
Note: Because Model S runs much quieter than a gasoline-powered vehicle, you may notice the
sound of the A/C compressor as it is operating. To minimize noise, reduce the fan speed.
120
Outside air is drawn into Model S (see
Although less efficient than recirculating the air in very hot or cold
climate conditions, this setting draws more air into the rear seating areas,
and is recommended when occupants are seated in the Tesla built-in rear
facing child seats.
Air inside Model S is recirculated. This prevents outside air (traffic fumes)
from entering, but reduces dehumidifying performance. Recirculating the
air is the most efficient way to cool the front cabin area. To prevent the
windshield from fogging in some conditions, briefly change the setting
every hour to draw in outside air.
Ventilation on page 122).
Model S Owner's Manual