2003 GMC Yukon Owner's Manual - Page 184

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. If you want to use the automatic mode, press AUTO and adjust the temperature by turning the temperature knob. The heater works best if you keep the windows closed while using it. Defogging and Defrosting You can use either defog or front defrost to clear fog or frost from your windshield. Use the defog mode to clear the windows of fog or moisture. Use the front defrost button to defrost the front windshield. -(Defog): Use this setting to clear the windows of fog or moisture. Press the mode button to select this setting. This setting will deliver air to the floor and windshield outlets. Press the front defrost button to defrost the windshield. The system will automatically control the fan speed if you select defrost from AUTO mode. If the outside temperature is 40°F (4°C) or warmer, your air conditioning compressor will automatically run to help dehumidify the air and dry the windshield. 0 (Front Defrost): Heating On cold days when using manual operation of the automatic system, choose floor mode to deliver air to the floor outlets. To warm or cool the air delivered, turn the temperature knob to the desired setting. 3-30