What Is a Wax Motor?

The wax motor is a drive unit consisting of a positive temperature coefficient thermistor (PTC), which is mounted on a sealed container filled with solid wax. When the solid wax is heated to a controllable temperature by an energized thermistor, the solid wax melts and expands, thereby driving a spring-loaded piston outward. This piston may drag the load in or out, depending on the orientation of the inner container of the wax motor housing and the configuration of the spring. When the thermistor is de-energized, the liquid wax cools and the spring returns the piston to its original position.