DIY Appliance Repair: Do You Know About Thermal Fuses?
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DIY Appliance Repair: Do You Know About Thermal Fuses?

I really do not know why it is, but it seems like every time someone calls me because their clothes dryer is not producing any heat, it turns out to be either a burned out heating element or a burned out thermal fuse. Most of the people who I know in the appliance repair business tell me they are experiencing the same thing. There was a time when there was just as good a chance that it would be a high-limit thermostat, a temperature selector switch, or even a bad contact on the timer. Today it is about equal chances that it is the heating element or the thermal fuse that is causing the problem.

Thermal fuses are different than normal fuses or even circuit breakers that respond to over circuit overload currents and short-circuit current. The amount of current flowing through a thermal fuse has no effect on them, unless the current flow is so high that it causes the thermal fuse itself to heat up to its temperature rating. Thermal fuses do not normally respond to current flow, only to temperature. The thermal fuse is a safety backup for the high-limit cutout thermostat. Both the high-limit thermostat and the thermal fuse are designed to keep the dryer from overheating to the point where a fire may start inside the dryer's drum. Normally the high-limit thermostat has an opening temperature sufficiently lower than that of the thermal fuse so the it will open and disconnect the heating elements before the dryer gets hot enough to destroy the thermal fuse. Unlike the high-limit thermostat, which will automatically reset itself once the dryer has cooled down sufficiently, a thermal fuse has to be replaced once it opens.

Locating the thermal fuse.

Thermal fuses may take several different configurations. They may look like those shown below.

From left to right these are the style thermal fuses/cutouts used in Whirlpool/KM, Frigidaire, Speed Queen, and GE/Hotpoint. Two popular configurations for thermal fuses used in older Whirlpool dryers are these two.

The actual location of the thermal fuses vary from one make and model dryer to another but they are always mounted on or very the heating element housing.

Testing a thermal fuse or cutout.

The thermal fuse or cutout is one of the easiest components to check that you ever encounter in your work with appliances. Testing them is a simple “go” or “No Go” test. They are either good or they are bad. There is no Grey area when thermal fuses are concerned. All you have to do is remove the wire or wires from one side of the thermal fuse and take a reading between the two terminals with your DMM set on it lowest resistance scale. A good thermal fuse will read “0.000” on the Digital Multimeter LCD (Liquid Crystal Display). A bad thermal fuse will read infinite resistance, which displays as an “O.L.” on most DMMs LCDs. When replacing a thermal fuse, make sure to use one with the right opening temperature, which is usually marked on the fuse or next to it on the wiring schematic.

What caused the thermal fuse to go bad?

Remember what I said before, current overloads or surges will not effect the thermal fuse, only heat can destroy it. That means that the dryers was severely overheating and that means that the the “High-Limit” thermostat did not open when it should have. The smart thing to do is replace the High-limit thermostat when ever you replace a thermal fuse. If you do not replace the high-limit thermostat at the same time you may be replacing the thermal fuse again in the very near future.

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Comments (3)

Jerry, you have constructed another award winning piece of information.  Thanks for sharing.

good work

Morning, Jerry. You are doing a great job on these DIY articles. The pictures are awesome too. They definitly enhance the articles - especially for people like me who simply pick up the phone and call "the men"! Have a great Earth Day!