A variable air volume ceiling diffuser includes a damper that is raised and lowered by a linkage that is controlled by a duct temperature sensor/actuator and one or more room temperature sensors/actuators. The linkage includes a heating slide movable for the heating mode and a cooling slide movable for the cooling mode. The duct temperature sensor/actuator selects the heating slide for movement by the room temperature sensors/actuators in the heating mode and selects the cooling slide for movement by the room temperature sensors/actuators in the cooling mode. The differential movement between the heating and cooling slides moves a roller that engages a profiled cam surface attached to two lever arms. As the roller moves along the cam surface, the lever arms pivot about their axis of rotation so that the damper moves upward to close the air inlet and downward to open the air inlet.