Abstract: The direction of air flow in an air blower is controlled by a plurality of rotationally adjustable blades (vanes) extending across an air flow passage. A motor is connected to the blades for rotating the blades between passage-opening and passage-closing positions and intermediate positions therebetween. A sensor senses the angular position of the blades and supplies a signal to a controller which compares that signal to a signal representative of a selected angular position of the blades. If the blades become-displaced by a force independent of the motor, the sensor signals the controller of such displacement, whereupon the motor is actuated to return the blades to the selected position.