GMC 2007 Acadia Owner's Manual page 208

Sensors
The solar sensor, located in the defrost grille in
the middle of the instrument panel, monitors
the solar radiation. Do not cover the solar sensor
or the system will not work properly.
208
The interior temperature sensor located 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
located 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.