Blower Control Button (328 Series)
WARNING: This page is about a different car, the 1996 BMW M3, 1996 BMW 328is, 1996 BMW 328i, 1996 BMW 318is, and 1996 BMW 318i. However, it is still accessible from the selected car via links, so may be relevant.
Blower control button allows volume of air entering passenger compartment to be varied. Airflow increases as "+" is depressed, and decreases as "-" is depressed. If "-" position is selected at minimum blower speed, all data disappears from display. Blower, heater, and A/C are deactivated, and flow of outside air is switched off.