Model ST Therma-Fuser VAV diffusers are 24in / 600mm square ceiling VAV diffusers with built-in temperature controls for VAV cooling and VAV heating. The round disc damper moves up to close and down to open, metering air flow (warm or cool) into the room in response to room temperature. The damper is mechanically positioned by a thermostat / actuator which is both a room thermostat and damper motor. Room air is positively induced over the thermostat / actuator for an accurate measurement of room temperature in both cooling and heating.