GMC 2007 Sierra - Manual (Page 240)

Air Conditioning
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(Air Conditioning): Press this button to turn
the air conditioning (A/C) compressor on and
off. The snowflake symbol will appear on
the display when the A/C is on and will turn off
when the air conditioning is off.
Pressing this button when the outside temperature
is too cool for air conditioning will make the
snowflake symbol flash three times and then turn
off to let you know the air conditioning mode is
not available. If the air conditioning is on and the
outside temperature drops below a temperature
which is too cool for air conditioning to be effective,
the snowflake symbol will turn off to let you
know the air conditioning mode has been
canceled.
When air conditioning is selected or in AUTO
mode, the system will run the air conditioning
automatically to cool and dehumidify the air
entering the vehicle. If you select A/C off while in
front defrost, defog or recirculation, the A/C
snowflake symbol will turn off, but the A/C
compressor will still run to help prevent fogging.
On hot days, open the windows long enough to let
hot inside air escape. This reduces the time it
takes for your vehicle to cool down. Then
keep your windows closed for the air conditioner
to work its best.
On cool, but sunny days while using manual
operation of the automatic system, use bi-level to
deliver warm air to the floor and cooler air to
the instrument panel outlets. To warm or cool the
air delivered, turn the temperature knob to the
desired setting.
In AUTO mode the system will cool and dehumidify
the air inside the vehicle. Also while in AUTO
mode, the system will maximize its performance
by using recirculation as necessary.
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