Refrigerator Thermistor [How to, Problems & Solutions]

Part of the reason a refrigerator smoothly runs is the presence of the thermistor. A refrigerator thermistor ensures the appliance does not become too cold or too warm. However, it can develop faults like other refrigerator parts. Learn how to solve thermistor issues in your refrigerator.

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What Does a Refrigerator Thermistor Do?

The thermistor in a refrigerator senses or detects the changes in the internal temperature. Its only responsibility is to signal the control board if the internal temperature changes. It reads the temperature and sends results to the control board. That way, the control board knows when to supply voltage to the cooling system, and how much to supply per time. It is crucial to have a functional thermistor in your refrigerator if the unit is to keep cooling.

How to Check a Refrigerator Thermistor

To check a refrigerator thermistor to see if it is faulty, do the following:

Disconnect the refrigerator from electric power or turn the circuit breaker off. Unmount the screw holding the temperature control housing to the refrigerator ceiling and drop it down. You will find the thermistor inside the housing. In some models, the thermistor will be behind a small cover on the back wall inside the refrigerator or on the wall.

Inspect the wire connectors on the thermistor to see if they are loose or damaged. Tighten noticeably loose connections and see if the thermistor resumes working. Otherwise, have a technician fix other wiring faults.

But if the connectors are not the problem, check the thermistor’s resistance with a digital multimeter. Uninstall the thermistor from the control housing by disconnecting the wire harness. Next, place the probes of the multimeter on the white wires extending from the thermistor. 

You may find the tech sheet taped to the refrigerator’s back or in the compressor compartment. Check it for the thermistor’s resistance range. Replace the thermistor if the resistance reading is off by over 10% of what the tech sheet says is the correct range.

How to Replace a Refrigerator Thermistor

Simply pull the thermistor free from the clip that secures it and disconnect the wire harness. Then, attach the new one to the wire harness and clip to secure it in place. Put the thermistor into position and replace the cover.

Note: You cannot bypass a refrigerator thermistor. Once the thermistor stops working, and you verify its resistance is not in range according to the tech sheet, replace it. Otherwise, the refrigerator may stop cooling.

How Do I Know If My Refrigerator Thermistor Is Bad?

The defrost function in your refrigerator will not run as it should. It may not run at all and over time, the evaporator coils will freeze. If you notice the refrigerator is no longer cooling as it should, and the coils have an accumulation of ice, the thermistor may be malfunctioning.

On the other hand, a refrigerator thermistor may malfunction and send signals that cause the control board to run the cooling system when the unit does not need it. In such a case, you may find the refrigerator cooling more than it should. It is another tell-tale sign that the thermistor is bad.

One other way to know your refrigerator has a bad thermistor is if the temperature is not steady. It may constantly fluctuate between cool and warm, without cooling the contents.

Are All Refrigerator Thermistors the Same?

All thermistors in refrigerators tend to be the same, though they may have different names. You may not find them in the same location in every refrigerator, but they always have the same part number. The number helps you buy the correct part, not necessarily model-specific.

Some models call a thermistor an evaporator sensor, while some call it a temperature sensor. But the general name is a refrigerator sensor.

Note that there are positive temperature coefficient thermistors and negative temperature coefficient thermistors. The resistance of a positive temperature coefficient thermistor will increase when the refrigerator’s internal temperature increases. But the resistance of the negative temperature coefficient thermistor decreases in such a case. Conversely, the resistance of a PTC thermistor drops when the temperature drops, while that of the NTC thermistor rises.

How to Test an RV Refrigerator Thermistor

Your RV refrigerator has a thermistor resistance range, just like every other type of refrigerator. Find the tech sheet with the required information and note the resistance range. Next, locate the thermistor in your RV refrigerator. Typically, it should have its sensor part clipped to one cooling fin. That way, it quickly detects a change in the internal temperature. However, the connection end may be somewhere else, such as the panel with lights or at the back of the eyebrow board.

Disconnect the wire harness attached to the thermistor and pull the thermistor out. Get a multimeter and connect its test leads to the wires of the thermistor. Then, check the resistance reading on the multimeter’s display. If it is not within the range according to the tech sheet for the specific model, replace the thermistor. Otherwise, test other refrigerator parts that are likely causing the problem.

Recap

Fixing different refrigerator parts saves service costs. But you must learn how to troubleshoot and repair the parts safely. That includes diagnosing and fixing a refrigerator thermistor. The part is also easy to find, as long as you know the part number to request. Contact the manufacturer for replacement parts if you cannot easily find one.

Typically, the part is not a challenge to remove and replace. But if you find it is too tedious, it is crucial to hire professional help. Otherwise, you risk damaging the refrigerator beyond repair.

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