Abstract: A fluid coupling device is disclosed in which flow of fluid from a reservoir chamber (35) into a fluid operating chamber (33) is controlled by a valve member (41), rotatable with a valve shaft (39). Rotation of the valve shaft (39) is normally controlled, in response to variations in ambient air temperature, by means of a bimetal coil (45), In accordance with the invention, a normally fixed outer tab (75) of the bimetal coil is attached to an output plunger (85) of an electromagnetic actuator (83). As a result, the operating condition of the fan drive can be changed between a disengaged condition and an engaged condition, in response to variations in a predetermined condition (73), other than ambient air temperature.