How to set Windshield Fans? What works for you?

They are adjustable and their purpose is to keep condensation off the windows, assisting the defrosters. You will even find them in class 8 over the road tractors. In the hot summer months, we adjust ours to blow air on us. Going south in February we use the to assist the defrosters in keeping the windshield and side driver's and passenger windows clear.