Abstract: A door and housing assembly for controlling air flow through the housing. The housing is adapted to be mounted in a ventilating system for controlling the direction and flow of air passing through the system. The door is actuated to move between two end positions where the respective air pathways are each sealed. The door can be positioned at any location between the end positions to control air flowing to the respective air pathways. The door includes guide pins on edges thereof that move along slots located in the inner sidewalls of the housing and guide the door between its end positions to locate the door in selected intermediate positions thereof. The slots for guiding the door may be steeply angled with respect to the seals so as to create minimal wiping of the respective seals upon engagement and dis-engagement between the door and seals at end positions of door travel.