2007 GMC Acadia Owner's Manual - Page 202

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 the windshield. Turn the right knob clockwise to select the defog or 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 less than 40°F (4°C). The recirculation mode cannot be selected while in the defog mode. Do not drive the vehicle until all the windows are clear. 0 (Defrost): The defrost mode is used 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 will automatically force outside air into your vehicle. The recirculation mode cannot be selected while in the defrost mode. The air conditioning compressor will run automatically in this setting, unless the outside temperature is less than 40°F (4°C). Do not drive the vehicle until all the windows are clear. AUX (Auxiliary): Press this button to turn the rear heating and air conditioning on. See Rear Air Conditioning and Heating System on page 211 or Rear Air Conditioning and Heating System and Electronic Climate Controls on page 212. 202