PURPOSE: To prevent malfunction of a plate due to freezing of condensate by providing the plate with a radial rib and making a recess in a part of the rib.

CONSTITUTION: A rib 17 is provided on the surface of a plate 21 in order to prevent warping thereof at the time of molding and a recess 18 is made in the recess 17 in order to accelerate condensate flow. Inner pressure of a temperature sensitive tube 10 encapsulating a gas is varied by temperature variation and a bellows 3 contracts when the temperature drops below a point for displacing the bellows 3. Consequently, a load lever 4 abutting against the bellows 3 is turned to close a chill outlet 1' with the plate 21. When the temperature rises, the bellows 3 elongates to turn the load lever 4 and the plate 21 begins to open the chill outlet 1'. When condensate adheres to the surface of the plate 21, water drops flows down along the rib 17 and flows out through the recess 18. Since water does not stand on the surface of the plate 21, malfunction of a damper opening/closing unit can be eliminated.