The Air Control Damper is simple, intuitive, and conveniently located on the radius of the ash lip. You can easily slide it open and closed with your foot! As you move the air control damper, a link moves the damper plate across two openings; one for primary air and one for secondary air. The ratio of primary air to secondary air has been determined in development. The damper plate is calibrated so that both primary and secondary dampers open and close with a single control, at a pre-determined ratio. A third damper automatically opens an air passageway that feeds the catalyst only (see Under the Hood 4).