2001 GMC Sierra 1500 Pickup Owner's Manual - Page 194

With the automatic setting, the air conditioning compressor automatically cycles when needed to cool the air. In cold weather, when the system senses the need for heat, the airflow will be directed out of the floor outlets. As the interior temperature approaches a desired setting, the blower speed will decrease. To maintain interior comfort, the airflow will adjust between the instrument panel air outlets and floor outlets. On bright sunny days in cool weather, the airflow may come out of the air conditioning and floor outlets (bi-level mode) to maintain comfort and prevent stuffiness. 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 outside air temperature, engine coolant temperature or the time since the engine was last started. As the coolant warms up, the fan speed will gradually increase and air will flow from the heater outlets, with some airflow to the windshield to prevent fogging under most normal conditions. Be careful not to put anything over the solar sensor located around the center of the instrument panel. This sensor is used by the automatic system to regulate temperature. Mode Knob -- Manual Operation The right knob on the control panel allows you to choose the direction of air delivery. You can choose to set the climate control system yourself, or let the system work for you by placing the system in AUTO mode. See "Mode Knob -- Automatic Operation" earlier in this section. PANEL: This setting directs most of the air through the instrument panel outlets and a small amount through the floor outlets. BI-LEVEL: Air is delivered through the heater floor outlets as well as the instrument panel outlets. HEATER: This setting directs most of the warmed air through the heater floor outlets and some air through the windshield defroster outlets. BLEND: Airflow is divided equally between the heater floor outlet and the windshield defroster outlets. The air conditioning compressor may run to dehumidify the air to prevent window fogging. 3-7