2000 GMC Yukon Owner's Manual - Page 169

DEFROST: This setting directs most of the air through the windshield defroster outlets, side window defroster outlets and some air through the heater outlets. When in the DEFROST mode, the air conditioning compressor may run to dehumidify the air to prevent window fogging. OUTSIDE AIR: Press this button to direct the system to use outside air. This is the setting which should be used for normal operation. Pressing the OUTSIDE AIR button will cancel the RECIRCULATION button. RECIRCULATION: Press this button to limit the amount of fresh outside air entering your vehicle. This is helpful when you are trying to limit odors entering your vehicle or attempting to quickly cool down the interior. Pressing RECIRCULATION will recirculate air continuously. RECIRCULATION is used when the fan control 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. In the 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. The auto recirculation feature will activate when: D the air conditioning system is activated, D the OUTSIDE AIR button is on, and D the vehicle load is high due to city traffic, extended idling or hot weather. The system will automatically switch to the recirculation mode to lower the system load and improve interior comfort. The OUTSIDE AIR and RECIRCULATION button LEDs will not change. The system will return to the OUTSIDE AIR function when the system load is reduced. A/C: Press this button to turn the air conditioning on and off. The system will cool and dehumidify the air inside the vehicle when the A/C light is on. Air conditioning will be automatically disabled when the outside temperature drops below a level at which air conditioning is effective. 3-4