GMC Acadia Owner's Manual page 212

8-8 Climate Controls
The interior temperature sensor, on
the instrument panel to the right of
the steering column, measures the
temperature of the air inside the
vehicle.
There is also an exterior
temperature sensor behind the front
grille. This sensor reads the outside
air temperature and helps maintain
the temperature inside the vehicle.
Any cover on the front of the vehicle
could cause a false reading in the
displayed temperature.
The climate control system uses the
information from these sensors to
maintain comfort settings by
adjusting the temperature, fan
speed, and air delivery mode. The
system may also supply cooler air to
the side of the vehicle facing the
sun. The recirculation mode will also
be used as needed to maintain cool
outlet temperatures.