Faulty Thermistor Symptoms


Thermistors serve a variety of purposes and can be found in everything from refrigerators and hair dryers to vehicles. Typically, they’re used as temperature sensors but can be extremely useful when it comes to current protection. So, what happens when a thermistor starts displaying incorrect readings? Learn more about faulty thermistor symptoms with Gateway Cable Company!

How Do I Know if a Thermistor is Bad?

For the most part, it’s easy to tell when you need to replace a thermistor. When a thermistor is failing, it’ll display incorrect temperatures, or you’ll see impossible temperature fluctuations. For example, you may initially get a reading of 210 degrees only to see the temperature drop to 189 degrees and jump back up again. Although other issues could be at play, if this happens frequently, the thermistor is likely failing.

Thermistors in car AC systems operate much like the smaller ones found in electronics — just on a larger scale. They measure temperatures and send resistance signals to the AC control module, allowing the system to automatically adjust so the cabin remains at the temperature you set. Faulty thermistor symptoms for vehicles are a little different. When a thermistor in a car is failing, the AC system will blow cold air for a short time or the blower will stop functioning correctly.

How to Test a Thermistor

Thermistors are important in regulating the temperature of electronic devices so it’s important to ensure they’re working properly. How can you do that? Easy! Check your thermistor by performing a test.

If you suspect thermistor failure, review our “how to test a thermistor” guide for more information! 

Meanwhile, here’s a broad overview of the process:

  1. Gather materials, including a multimeter, heating device, and of course, thermistor.
  2. Read the current on your thermistor.
  3. Set the resistance reading to the rated value; if you can’t, then you will definitely need a new thermistor. If you can, move to step four.
  4. Heat the thermistor, and be sure to take note of any changes, which should be near-immediate. If they’re not, your thermistor is most likely in need of replacing.

Whether you’re testing an A/C thermistor or waning to know how to check the thermistor on a dryer, this process is generally similar. 

How to Tell Before a Thermistor Goes Faulty

Want to get ahead of thermistor failure? Generally speaking, symptoms of a faulty thermistor present themselves before the thermistor goes completely bad. Usually, they are the same or similar issues as faulty thermistor symptoms. So, what are symptoms of a faulty thermistor before it goes bad? They include:

  • Temperature fluctuations
  • Incorrect temperature readings
  • Blower motor broken or cold air for only a short time (in car A/C systems with thermistors)

While these may indicate a thermistor that’s not quite right, you can confirm for sure by testing your thermistor! That’s the most surefire way of knowing if a thermistor is faulty.

What Causes Thermistor Failure?

Usually, thermistor failure is caused by an open circuit due to mechanical separation between the resistor element and lead material. This can happen as a result of improper handling, thermal mismatch, or heat damage. Another common reason thermistors fail is simply aging. Over time, the thermistor circuit becomes less accurate and displays incorrect temperatures. In this case, it’s easiest to choose a replacement.

How to Choose a Replacement Thermistor

There are two main types of thermistors. The first is negative temperature coefficient (NTC) thermistors. NTC thermistors decrease resistance when temperatures increase. The second is positive temperature coefficient (PTC) thermistors, which increase their resistance when the temperature increases. If you need a replacement thermistor, ask yourself the following questions:

  • What’s the base resistance of the thermistor you’re replacing?
  • What base resistance does your application need?
  • How do resistance and temperature relate to this application? Should resistance decrease or increase as the temperature rises?
  • What’s the ideal thermistor size and style for your application?

Shop for Replacement Electrical Parts at Gateway Cable Company!

When you need military-grade thermistors, cable assemblies, plugs, and more, Gateway Cable Company is your trusted source. We’re ISO 9001:2015 certified and DFARS compliant, ensuring the highest level of reliability for our customers. Contact us to learn more about faulty thermistor symptoms, how to test or check and A/C thermistor, or to request a quote on a replacement!