The wax motor is used on many appliances to actuate components from washer dispensers, to door locks, and even vents in microwaves and dishwashers. They are often compared to solenoids because they both provide the same linear movement when operated and can be used where a short range of motion is needed. But unlike solenoids that use a magnetic field for arm actuation, wax motors use a small block of wax to provide movement.
Wax motors consist of few parts as shown in the photo below, and require no maintenance. At the heart of the assembly is the wax block, shaft, and PTC heater. To operate, an electric current is connected to the heater mounted to the side of the block. As heat is generated, the wax core within the block turns to a liquid and begins to expand. This expansion pushes against the shaft and then on to the actuator arm. When current is removed, the heater will slowly cool causing the wax to return to a solid state. The arm and shaft return to the home position with the aid of a countering spring mounted within the housing.
Wax motors are often used where a slow, gentile movement is desired over the quick snap of a solenoid. They are slow to actuate and to return, and because there is no magnetic coil used, they are less likely to fail if the shaft is stopped during its full travel. Wax motors can be easily checked for operation by measuring resistance between the two terminals. A resistance of 1500ohms is about right, but as long as you are not reading an open or shorted circuit, the wax motor should be functional.
The video below demonstrates the use of a wax motor in a door latch assembly from a front load washer. The wax motor is not used as the primary locking mechanism, but rather a secondary system that actuates before the spin cycle. This slow movement makes the wax motor the ideal component for this function.