2001 GMC Sierra 1500 Pickup Owner's Manual - Page 193

AUTO: If the knob is in AUTO, the fan speed will vary as the system maintains the selected temperature. When both the fan control and mode knobs are in the AUTO position, the system will then automatically maintain the desired cabin temperature as selected by the temperature knob. Manual control of functions is also available. Temperature Knob The middle knob on the control panel lets you select the desired air temperature in your vehicle. This knob will allow you to adjust the interior air temperature independent of the function knob setting. Move the knob clockwise toward 82 for warmer air. Move the knob counterclockwise toward 66 for cooler air. When the system is set for automatic operation, sensors will control the fan/blower speed. Full Hot: If you turn the temperature knob past 82_F (28_C), the system will go into the "full hot" mode. The system will remain at that maximum heating setting and the fan will blow at the speed the fan knob is set to. If the fan is in AUTO, it will run at full speed. Full Cold: If you turn the temperature knob past 66_F (19_C), the system will go into the "full cold" mode. The system will remain at that maximum cooling setting and the fan will blow at the speed the fan knob is set to. If the fan is in AUTO, it will run at full speed. Mode Knob -- Automatic Operation The right knob on the control panel allows you to choose the direction of air delivery. When the system is set for automatic operation, sensors will control the air delivery mode. Air will come primarily from the floor or instrument panel outlets, with some air directed to the windshield to prevent fogging. When the system is in AUTO mode, the air conditioning light will turn on, and the recirculation and outside air lights turn off. With the system in full auto control (both the fan and mode knobs in AUTO), you still have the ability to override any function. However, continually overriding the outside air or the A/C compressor will limit the ability of the system to cool the vehicle quickly. If you push a button for a function which is not available, the light next to that button will flash three times to alert you that it's not available. To find your comfort zone, start with the 74_F (23_C) setting and allow about 20 minutes for the system to adjust the temperature if necessary. 3-6