2003 GMC Sonoma Owner's Manual - Page 149

Defogging and Defrosting 9 (Defrost): This mode directs most of the air to the windshield and the side window outlets, with only a little air directed to the floor outlets. To circulate outside air and to help clear the windshield quickly, do the following: 1. Select the blend mode. 2. Select the temperature. (Blend): This mode can be used on cool, humid days to keep the windshield and side windows clear. +3 3. Select the highest fan speed. 3-22