How to Check a Thermistor in an RV Refrigerator

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When an RV fridge starts to generate excess frost and turns the milk into popsicles, it is time to check the thermistor. A thermistor is a resistance-based temperature sensor and testing its accuracy is the first step toward determining whether the problem lies here, or elsewhere. Thermistor failure is a common issue in RV refrigerators and generally causes the temperature to fall too low. Fortunately, replacement thermistors are relatively inexpensive and repair manuals are available online.

Things You'll Need

  • Thermistor specification sheet
  • Refrigerator repair manual
  • Flashlight
  • Screwdriver
  • 2 small pieces of wire
  • Ohmmeter or multi-meter

Prepare to Check the Thermistor

  • Check the resistance range for your model of fridge. The best value to reference is the resistance range for about freezing. (As the thermistor gets colder, resistance increases, and vice versa.)

  • Read instructions on where to find the thermistor and how to reach its connection end.

  • Locate the thermistor. The sensor part of the thermistor is typically clipped onto one of the cooling fins at the back of the refrigerator, but the connection end is found elsewhere. In many fridges that may be behind the eyebrow board, the panel with indicator lights and switches found somewhere toward the top of a fridge.

  • Disconnect the thermistor. Each fridge model is different. An example procedure involves opening the main fridge or freezer door, unscrewing the eyebrow board, pulling the board forward and disconnecting the thermistor cable.

Check the Thermistor

  • Attach an ohmmeter to the thermistor wires. You can pick up inexpensive ohmmeters at most hardware stores. Either of the ohmmeter's two connections can be attached to either of the thermistor's two connections.

  • Ohmmeters measure resistance; multi-meters may measure voltage, resistance and current. Use the portion of the dial marked for resistance (it will most likely have an omega symbol to denote ohms). Turn the dial until it shows the scale that gives the largest number of significant digits.

  • Check the ohmmeter screen for measured resistance. Compare to the given range for that particular model of fridge.

  • If the thermistor measures in the specified range, it is not faulty and the problem lies elsewhere. If it does not, it is time to replace the thermistor.

Tips & Warnings

  • To extend the connection between ohmmeter and thermistor, attach two pieces of wire as an extension.
  • Setting the ohmmeter incorrectly will result in inaccurate readings, which could result in the belief that the thermistor has failed when it has not.
  • Short people may need to use a stool to access the eyebrow board.

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