Thermistor

A “thermistor” is a thermally sensitive resistor. It changes resistance values based on temperatures. Appliances with control boards use them to determine the temperatures inside a unit.

Appliances use these for accurate temperature measurements as they are very precise.

Testing

You DO NOT check a thermsitor by checking continuity. You test them by comparing their resistance to a chart that the manufacturer provides at certain temperatures.

For this fridge, at 77°F, you should see somewhere around 2.7kΩ.

You can submerge the thermistor in ice water, and expect it to get to around 36°F, and show a resistance value of about 8kΩ

Symptoms of Failure

Overcooling in the Fridge. If fridge thermistor is out of spec, it might indicate to the control board that the temperatures are 45°F, when in reality it’s 28°F. The board will keep cooling the fridge section, and the customer willl see their items freezing.

Board Logic

On a lot of fridges, in diagnostics, you will see “Pass”/”Fail” tests for the thermistors. If you see a “Pass,” all this means is that the control is seeing the thermistor in a certain range. The “pass” designation does not indicate that the thermsitor is refelecting accurate temperatures.

A “fail” designation indicates a shorted or open thermistor, and you’d want to investigae further to determine if you’ve got a faulty thermistor, or a damaged wire somewhere.