Understanding Wax Motors

[TechnicianBrian]

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 idea component for this function.

[JWWebster]

Let me get this straight. They use a dang hunk of wax melted to expand and push the pin forward to lock the door or dispense soap or rinse agents, but how is it that the wax motor Fry's the board's resister? Is it the wax itself becomes dissipated and thus the resistance in the heater becomes nill and that is what spikes the board by frying the resister on them fancy maytag washers? Can you spell defect? I noticed they has the new and improved red wax motors to replace them Asian productions. Give me your opinion mighty one. BTW did I mention you are the baddest of the bad? You are the 3rd mofo to drop da bomb on da bomb! That is my assessment. 

[TechnicianBrian]

Hey Thanks JW,

The wax motors are neat, but I think the big problem is the tolerance of the heaters seems to be very loose in the manufacturing process.  I have yet to find two that measure the same either warm or cold so it is probably difficult to engineer a circuit that will take that kind of sloppy production into account.  But they seem to find their way into appliances left and right so they are most likely here to stay. 

Brian