Abstract: An improved thermally responsive freeze actuator for operation of an air conditioning throttle valve between the evaporator and compressor to maintain the pressure and temperature of evaporator refrigerant above a freezing level. The improved actuator includes a rigid-walled tubular portion containing water and an attached axially extendable bellows portion. The water in the tubular portion is separated from the bellows portion by a deep cup shaped member or diaphragm of elastomeric material. The deep pocket of the diaphragm encloses one end of a push rod. As the water surrounding the pocket portion of the diaphragm changes to ice the rod is moved axially from the tubular portion. The other end of the rod engages the bellows which may be stationary mounted to a frame member to cause the entire actuator to move with respect to a valve seat.