Appliance tip of the week.
Most Frequent Causes for a bad defrost thermostat.

The defrost thermostat can be found in the evaporator coils.

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Defrost thermostat

A bimetal switch used to open the electric circuit to the defrost heater once a set temperature is obtained. The defrost cycle will continue until the timer (or electronic board) advances into the cooling cycle, however the heater will no longer be energized. This thermostat will reset to a closed position once a set colder temperature is again reached. These have been called defrost thermostat, defrost limit switch, defrost heater switch, defrost stat, bi-metal defrost thermostat.
How can a defrost thermostat fail?

A defrost thermostat can fail open and the evaporator coils will all get plugged up with white snow or frost. It can loose it's temperature value and fail to open or close at the correct temperatures. It can also stick on and keep the defrost heater on too long and this could effect or warm up the freezers temperature.

Can it ohm ok and still be bad....yes!

Can it open and close and still be bad....yes!

Can it intermittently work?....yes!

Can they physically break?....yes!

Can they loose their temp rating?....yes!

Can they stick?....yes! (open or closed).

A broken defrost thermostat, looks like moisture gets inside and freezes and this pops the defrost thermostat open and it is now bad for sure! If you see yours bulging apart like the picture = new defrost thermostat time for sure.

Picture linked here.

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Refrigerator Defrost Thermostat Testing

I find that most defrost thermostats are fairly cheap to purchase so I don't put too much time into checking one. If I suspect that the defrost thermostat is bad I would just replace it with a new one.

Refrigerator defrost thermostat. The thermostat clips onto the evaporator.

Refrigerator defrost thermostat, clip-on

Wire harness *Comes with defrost thermostat

Refrigerator defrost thermostat

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