This article explains how to use the PHN 90 by Boretti.
Light key: Lights ON/OFF. Key 1: activates the motor at level-one suction power; press key 1 to turn it off. Key 2: activates the motor at level-two suction power; press key 2 to turn it off. Key 3: activates the motor at level-three suction power; press key 3 to turn it off. Key 4: activates the motor at level-four suction power; press key 4 to turn it off. To turn off the mo or, the suction power keys must be in their original position.