GMC Yukon XL 2013 Owner's Manual page 259

Sensors
The solar sensor, located in the
defrost grille in the middle of the
instrument panel, monitors the solar
heat. Do not cover the solar sensor
or the system will not work properly.
The interior temperature sensors
located in the headliner above the
driver side seat and if equipped, in
the headliner above the second row
seats measure 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.
Climate Controls
The climate control system uses the
information from these sensors to
maintain your comfort setting by
adjusting the outlet temperature, fan
speed, and the 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.
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