Testing Thermistors with an Ohm Meter

Modern refrigerators that have electronic controls use a special electronic device called a thermistor to sense temperatures. Are these devices complicated to test and trouble shoot? Not in the least. See Figure 5.42 of a replacement thermistor meant to clip onto a line of the evaporator of a typical frost free refrigerator. There are just two wires going to them. To test the operation you just need to test the resistance, change the temperature of the thermistor and check the resistance again to see if it's responding. If you're testing a thermistor on a GE refrigerator you could compare it directly to the values on Figure 5.43.

Figure 5.42 Typical replacement thermistor

When testing a thermistor, do you have to be this precise? No just use the information on Figure 5.43 to see if the device is responding as it should. The chance of a thermistor ever going "out" of temperature range would be next to impossible. Ninety nine percent of the time if you find a faulty thermistor it will either be a dead short, open altogether, or won't respond to temperature change. First measure the resistance and record it, somehow cause the temperature to decrease by perhaps placing it in a glass of ice water. Or cause it to increase with a hand held hair dryer and see if it responds. It should be noted that the chart on Figure 5.43 shows typical thermistor vales for a GE refrigerator and a thermistor from a different model may show different readings. Generally the resistance across its two wires should decrease if you warm the device up or increase if you cool it down

* Note: There may be unforeseen situations in the immerging use of this device specific to domestic refrigeration. If as a user of this information you ever find a contradiction here and you have had to replace a thermistor because it was "out " of calibration, please report the issue to the author so this article can be revised.

Figure 5.43 Resistance across the leads of a thermistor at different temperatures
( data from a GE thermistor used on Arctica designs)