2002 GMC Yukon Owner's Manual - Page 184

(Blend): Airflow is delivered through the floor outlets, center floor console outlets (if equipped), the windshield defroster outlets and the side window defroster outlets. The air conditioning compressor may run to dehumidify the air to prevent window fogging. (Defrost): This setting directs most of the air through the windshield defroster outlets, side window defroster outlets and some air through the floor and center floor console outlets (if equipped). If air from the center floor console is not desired, or more defroster performance is desired, turn the vents off at the console. When in defrost mode, the air conditioning compressor may run to dehumidify the air and limit window fogging. Mode Buttons (Outside Air): Press this button to direct the system to use outside air. Pressing the outside air button will cancel the recirculation button. (Recirculation): Press this button to limit the amount of outside air entering the vehicle. This is helpful when you are trying to limit odors entering the vehicle or attempting to quickly cool down the interior. Pressing recirculation will recirculate air continuously. Recirculation is used when the fan is OFF to limit odors, outside air and dust from entering your vehicle. All button lights will go off. The last setting selected will activate when the blower is turned back on. Pressing the recirculation button will cancel the outside air button. To return to normal operation and to prevent stale air, be sure to return to outside air. Between floor and blend mode, outside air is forced to reduce window fogging. If the recirculation button is pressed, the LED indicator will flash three times indicating that forced outside air is activated and recirculation is not available. 3-4