1999 GMC Yukon Owner's Manual - Page 155

yellowblue Heater and Air Conditioning Control System (If Equipped) Temperature Knob The middle knob on the control panel lets you select the relative temperature of the air flowing into the passenger area of your vehicle. This knob will allow you to adjust the relative air temperature independently of the function knob setting. Move the knob clockwise to the red area for warmer air. Move the knob counterclockwise to the blue area for cooler air. Mode Knob The right knob on the control panel allows you to choose the direction of air delivery. The control knob can be placed in any position between any two mode settings to blend the flow of air. Fan Knob The knob on the left side of the heating system control panel controls the fan speed. The knob has four speed positions. To increase airflow, move the knob toward HI. To decrease airflow, move it toward LO. To turn the fan off, move the knob to OFF. If you have the air conditioner on, moving the fan knob to OFF also turns off the A/C compressor. While driving with the fan knob in OFF, ram airflow will vent to the floor outlets. The mode knob will not redirect ram airflow to other selected outlet positions. This is a normal operation for the OFF position. VENT: This setting directs air through the instrument panel outlets. VENT/HEAT: Use this setting to divide airflow between the floor outlets and instrument panel outlets. HEATER: This setting directs air through the floor outlets. DEFOG: This setting directs air to the heater outlets and toward the windshield. 3-3