2007 GMC Sierra 1500 Pickup Owner's Manual - Page 240

Air Conditioning # (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. 240