the cryogenic refrigerator includes a movable displacer within an enclosure having first and second chambers of variable volume . a refrigerant fluid is circulated in a fluid path between said chambers and correlated with movement of the displacer . a spool valve controls introduction of high pressure fluid and low pressure fluid to said chambers . the displacer movement is controlled by an electric motor which has a cam for reciprocating the spool valve member . the refrigerator is converted into a source of heat by reversing the direction of rotation of said electric motor .