A system for controlling airflow in a plenum, that comprises a worm gear and planetary gear that are removably coupled to a worm shaft and planetary shaft, respectively. The planetary shaft controls the movement of a damper between an open position permitting maximum airflow through the plenum, and a closed position restricting airflow through the plenum. A motor or gear-motor is positioned at the plenum for driving the worm shaft. The motor is controlled by a remotely located controller that includes a power supply for operating the motor and that has a display providing a continuous indication of the position of the damper between the open and closed positions. The controller is connected to the motor through a cable with a detachable electrical connection between the cable and the controller, such as a jack and plug. A wall plate for housing the electrical connection is mounted on a wall or other structure. The wall plate has a first plate for housing the jack and a second plate with a flexible flange for removably securing the jack in the housing by snap fit insertion.