2001 GMC Sierra 1500 Pickup Owner's Manual - Page 191

BLEND: Airflow is delivered through the heater floor outlets, center floor console outlets (if equipped), the windshield defroster outlets and the side window defroster outlets. The air flow can be divided between HEATER and DEFROST depending upon where the knob is placed between the settings. 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 heater outlets and center floor console outlets (if equipped). If air from the center floor console outlets is not desired or more defroster performance is desired, turn the vents off at the console. 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. Pressing the OUTSIDE AIR button will cancel the RECIRCULATION button. RECIRCULATION: Press this button to limit the amount of 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 the OUTSIDE AIR. Between HEATER 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