Cadillac 2002 DeVille Owner's Manual page 207

To avoid blowing cold air in cold weather, the system
will start at reduced fan speeds until warm air is
available. The length of reduction depends on the
outside air temperature, engine coolant temperature
or the time since the engine was last started. As the
coolant warms up, the fan speed will gradually increase
and air will flow from the floor outlets, with some
airflow to the windshield to prevent fogging under most
normal conditions.
If you select defrost mode or a fan speed, this function
will be skipped and the system will be in manual mode.
If you leave your vehicle, the system will recall the
control setting the next time you start your engine,
except for recirculation and defrost.
Electronic Solar Sensor
The sensor monitors the sun's solar radiation. It is located
on top of the instrument panel near the windshield.
When the climate control system is in AUTO, the system
uses this information to automatically make the necessary
temperature and airflow adjustments to maintain your
comfort. The climate control system may supply cooler air
to one side of your vehicle, if that side is facing the sun.
Be sure not to cover the sensor on top of the instrument
panel. If you do, it will not work properly.
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