2008 GMC Yukon Owner's Manual - Page 202

When AUTO is selected, the air conditioning operation and air inlet will be automatically controlled. The air conditioning compressor will run when the outside temperature is over about 40°F (4°C). The air inlet will normally be set to outside air. If it is hot outside, the air inlet may automatically switch to recirculate inside air to help quickly cool down the vehicle. The light on the button will illuminate in recirculation. 2. Set the driver's and passenger's temperature. To find your comfort setting, start with a 74°F (23°C) temperature setting and allow about 20 minutes for the system to regulate. Use the driver's or passenger's temperature buttons to adjust the temperature setting as necessary. If you choose the temperature setting of 60°F (15°C), the system will remain at the maximum cooling setting. If you choose the temperature setting of 90°F (32°C), the system will remain at the maximum heat setting. Choosing either maximum setting will not cause the vehicle to heat or cool any faster. Be careful not to cover the solar sensor located on the top of the instrument panel near the windshield. This sensor regulates air temperature based on sun load and also turns on the headlamps. For more information on the solar sensor, see "Sensors" later in this section. To avoid blowing cold air in cold weather, the system will delay turning on the fan until warm air is available. The length of delay depends on the engine coolant temperature. Pressing the fan switch will override this delay and change the fan to a selected speed. O (On/Off): Press this button to turn off the climate control system. Outside air will still enter the vehicle, and will be directed to the floor. This direction can be changed by pressing the mode button. Recirculation can be selected once vent or bi-level mode has been selected. The temperature can also be adjusted using either temperature button. If the air delivery mode or temperature settings are adjusted with the system off, the display will illuminate briefly to show you the settings and then return off. Press the on/off button or the up down arrows on the fan switch, the defrost button, AUTO button, or the air conditioning button to turn the system on when it is off. 3-28