Cadillac 1999 DeVille Owner's Manual page 165

OFF: Press this button to turn the system off. Fresh air
will continue to flow through the vehicle, and the
system will try to maintain the previously set
temperature. The outside temperature will show on the
display when the system is OFF.
AC: Press this button to turn the air conditioning on and
off. The system will cool and dehumidify the air inside the
vehicle. In the AUTO mode, the display will show that
AC is active, but the air conditioning compressor only
operates when the system determines it is needed.
RECIRCULATION: Press this button to limit the
amount of fresh air entering your vehicle. This is helpful
when you are trying to cool the air quickly or limit odors
entering your vehicle. In the AUTO mode, the system
will use recirculation as necessary to cool the air.
Pressing the recirculation button will change the
operation to a manual mode and the air will recirculate
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non stop. Press this button again to turn off the
recirculation feature.
If you notice the windows fogging, press the
recirculation button to exit the recirculation mode.
Electronic Solar Sensor
The sensor monitors the sun's solar radiation and is
located on top of the instrument panel near the
windshield. The ECC panel uses this information to
automatically make the necessary temperature and
airflow adjustments to maintain your comfort.
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