2007 GMC Acadia Owner's Manual - Page 209

The climate control system uses the information from these sensors to maintain your comfort setting by adjusting the outlet temperature, fan speed, and the air delivery mode. The system may also supply cooler air to the side of the vehicle facing the sun. The recirculation mode will also be used as needed to maintain cool outlet temperatures. Defogging and Defrosting Fog on the inside of the windows is a result of high humidity (moisture) condensing on the cool window glass. This can be minimized if the climate control system is used properly. There are two modes to clear fog or frost from your windshield. Use the mode up and down arrows to select the defog mode. Use the defrost button to select the defrost mode. - (Defog): The defog mode is used to clear the windows of fog or moisture and warm the passengers. This mode directs air to the windshield, floor outlets, and side window vents. When you select this mode, the system turns off recirculation and runs the air conditioning compressor unless the outside temperature is close to freezing. The recirculation mode cannot be selected while in the defog mode. Do not drive the vehicle until all the windows are clear. 0(Defrost): Press this button to remove fog or frost from the windshield more quickly. This mode directs most of the air to the windshield and side window vents and some to the floor vents. In this mode, the system automatically forces outside air into your vehicle. The recirculation mode cannot be selected while in the defrost mode. The air conditioning compressor runs automatically in this setting, unless the outside temperature is close to freezing. Do not drive the vehicle until all the windows are clear. 209