2010 GMC Acadia Owner's Manual - Page 251

Climate Controls 8-7 0 (Defrost): Press to turn the defrost on or off. This mode quickly clears the windshield of fog or frost. Air is directed to the windshield, side window, and floor vents. In this mode, outside air is pulled inside the vehicle. The air conditioning system runs automatically in this setting, unless the outside temperature is less than 4°C (40°F). Do not drive the vehicle until all the windows are clear. While in defrost mode, if the PASS button is pressed, the PASS button indicator flashes three times to show that the passenger climate control system cannot be activated. If the passenger temperature buttons are adjusted while in defrost mode, the driver temperature indicator will change. The passenger temperature will not be displayed. When returning to bi-level, vent, or floor mode, the previous temperature settings displays in place of any change made while in defrost mode. Air Conditioning # (Air Conditioning): Press to turn the air conditioning (A/C) on and off. An indicator light comes on when A/C is on. The A/C does not work when the outside temperature is below 4°C (40°F). If # is pressed the indicator flashes three times and turns off to show that the A/C mode is not available. If the A/C is on and the outside temperature drops below a temperature which is too cool for air conditioning to be effective, the A/C indicator turns off to show that the A/C mode has been canceled.