How to Troubleshoot a Thermistor

Ohmmeters generate electricity to test how much resistance lies between the two terminals.

Thermistors use temperatures to control the flow of electricity. Electrical current is increased as the thermistor becomes either warmer or colder, depending one which type of thermistor is used. Thermistors are commonly employed in thermostats, to control the flow of electricity to an air-conditioner or heater, based on the outside temperature. Thermistors are also commonly employed by auto manufacturers to deliver vital information about engine coolant temperatures. Thermistors are often used as a safety measure, and should be tested when a temperature-based item ceases to function. Faulty thermistors are generally designed to default to "Off" when they malfunction.

Things You'll Need

• Multimeter
• Heating source

Instructions

1. Remove the thermistor from the appliance.

2. Set your multimeter to the "Resistance" or "Ohmmeter" setting.

3. Attach the black pin of the multimeter to the neutral lead on the thermistor. Use clothespins to hold it in place if your multimeter leads lack alligator clips.

4. Attach the red pin of the multimeter to the "hot" or "positive" lead on the thermistor. Again, clip the lead to the thermistor so you can continue using your hands while the resistance is being tested. After attaching, note whether the resistance is infinite, meaning no electricity can flow through it, or something else.

5. Warm the end of the thermistor using your heat source. As it warms, watch what happens to the resistance setting. If there is no change from room temperature to warm, consider applying more heat. If the thermistor become so warm that you cannot touch it, yet the ohmmeter does not indicate any change in resistance, this indicates a nonfunctioning thermistor.

Tips & Warnings

• Though thermistors are generally designed to shut down under extremes, they can be constructed to react to any number of stimuli. Consider the place where the thermistor was installed when you formulate a plan for changing its temperature. Placing it in the freezer for and hour might yield better testing results than applying heat.

• Exercise caution when working with electrical appliances. Ensure that the item with the thermistor is unplugged before removing the thermistor.

• The ohmmeters requires electricity to be generated, often by a replaceable battery. If you have not used your multimeter in a while, test the meter against various conductors to ensure that the meter moves. Dead batteries in the multimeter always read infinite resistance, which give you a false reading on the thermistor.

References

• Ohmcheck: How to Test a Thermistor