Abstract: Motor apparatus which converts hydraulic energy and change of state heat energy to mechanical energy. The motor includes a main chamber divided by a piston into first and second portions. During a first half cycle or hydraulic power stroke, a valve places the first portion of the chamber in fluid communication with a source of pressurized, saturated liquid and the second portion of the chamber in fluid communication with a drain port. A switch senses the end of the hydraulic power stroke and causes the valve to move to a second position wherein the first and second portions of the chamber are placed in fluid communication with one another to form a common motor chamber and drive the piston in an expansion power stroke. Power is derived from the working fluid during the piston stroke in each direction. The motor finds particular application for energy recovery in an absorption refrigeration system.