The invention consists of a unit 10 including a two-piece, snap together housing made of elements 40 and 50 which forms the orifice seat and the transitions which direct moisture away from the seat area and prevents the accumulation of moisture in the seat area. Left-Hand (LH) housing 50 contains a blind journal and right-hand (RH) housing portion 40 contains a through journal for support and location of the gate 60. Also integral to the RH housing portion 40. are bosses for attaching the snap action switches 80, which determine gate orientation and mounting a gear motor 90, and can generally be referenced as “gate position sensors”. Such switches could also be replaced with other gate position sensors such as know in the art such as hall effect switches, magnetic switches, optical devices, etc. The gear motor provides the driving torque to the gate 60 through a cam-coupling 70, which has four switch detents 71, oriented to an internal shaft indexing means. Insulation members 20, 30 minimize condensation in the housing portions 40, 50 by separating the cold air flowing through housing from the warmer air which surrounds the damper assembly 10. In operation, a temperature sensing device/system senses the compartment temperature and energizes the gear motor 90, rotating the gate 60 into the open or closed position. The position of the gate 60 is determined by the combination of the states of the two switches 80. When used with mechanical controls the gate will rotate 90 degrees per cycle. When used with an electronic control system, the gate 60 can be rotated to any desired position and then stopped.