Why does AC blows through defrost on a Van?

The AC system in a van may blow air through the defrost vents to help clear the windshield and Windows of fog or frost. This occurs because the defrost setting directs air from the AC system, which is dehumidified, onto the glass surfaces. By reducing humidity, the AC helps improve visibility. Additionally, the temperature difference between the cold air and the warm glass can facilitate quicker defogging.