Symptoms of a Bad Refrigerator Thermistor and How to Fix It

A refrigerator thermistor plays a critical role in keeping your food fresh. When it goes bad, it can throw your fridge off balance, leading to a variety of problems. If your fridge isn’t working like it should, it’s crucial to understand the symptoms of a bad thermistor. In this guide, we’ll walk you through everything you need to know about thermistors, from recognizing the signs of a faulty one to fixing or replacing it.

What Is a Refrigerator Thermistor and How Does It Work?

Before diving into the symptoms and how to handle a bad thermistor, it’s important to first understand what a thermistor is and how it functions in your refrigerator.

A thermistor is a temperature sensor that monitors the internal temperature of your refrigerator and freezer. Its job is to send temperature readings to the control board, which uses this data to adjust the cooling levels. By doing so, the thermistor helps the fridge maintain the right temperature to keep food fresh. Without a properly working thermistor, your fridge could end up being too warm or too cold, causing food spoilage or ice buildup.

There are two main types of thermistors: negative temperature coefficient (NTC) and positive temperature coefficient (PTC). NTC thermistors are more commonly used in refrigerators. The main difference is that the resistance of NTC thermistors decreases as the temperature increases, while PTC thermistors do the opposite. Understanding which type your refrigerator uses isn’t crucial for the homeowner, but it’s good to know that most modern fridges use the NTC type.

Common Symptoms of a Bad Refrigerator Thermistor

Now that you know what a thermistor does, let’s take a look at some of the most common symptoms that indicate it may be going bad. If you’re noticing any of the following, it’s likely time to check your thermistor.

1. Inconsistent or Wrong Temperatures

If your fridge is running too warm or too cold, a malfunctioning thermistor could be the cause. The thermistor’s job is to regulate the cooling system based on temperature readings, so if it’s sending faulty information to the control board, the fridge can’t properly adjust its cooling settings.

For example, if the thermistor is reading a temperature that’s too high, the control board might think the fridge is warm and turn on the cooling system for longer than necessary. On the other hand, if the thermistor reads a low temperature, the cooling system may not run enough, causing your food to get too warm.

You might notice food in the fridge freezing or thawing unexpectedly, or your ice cream might be melting even though the freezer is set to a low temperature.

2. The Refrigerator Runs Too Often or Not Enough

Another sign of a bad thermistor is when your refrigerator keeps running nonstop, or the opposite — it doesn’t turn on at all. If the thermistor is faulty, it might not send the correct signals to the control board about the internal temperature, making the fridge work overtime or fail to activate when needed.

If your refrigerator seems to never stop running or is always on, it’s an energy-wasting issue that can also affect the lifespan of your fridge. On the other hand, if the fridge doesn’t run enough, it could lead to spoiled food. Either way, a faulty thermistor can cause serious cooling problems.

3. Frost Build-Up or Ice Inside the Fridge

A thermistor that doesn’t work properly may cause frost to build up in your refrigerator or freezer. This is because the cooling system might not stop running when it should, causing excessive cold air to freeze moisture inside the fridge. If you notice ice accumulating inside the fridge, especially in areas like the freezer or along the walls, a bad thermistor could be the cause.

Frost or ice build-up can damage food, make it harder to access certain items, and even cause the refrigerator’s components to work harder than necessary. This can lead to a more significant problem, such as a frozen evaporator coil, which could make repairs more costly.

4. Error Codes on Your Refrigerator’s Display

Many modern refrigerators come with a digital display that shows error codes when something goes wrong. If the thermistor is failing, your refrigerator may display an error code. Common error codes related to temperature sensors include codes like “Err,” “SENSOR,” or “F1.” These codes indicate that the refrigerator is having trouble receiving or interpreting the temperature data from the thermistor.

Consult your refrigerator’s manual to understand what specific error codes mean. If your fridge is displaying a code related to the thermistor or temperature control, it’s a strong indication that the thermistor may be the issue.

5. Overcooling or Undercooling in Certain Areas

Another subtle symptom of a bad thermistor is uneven cooling within the fridge. You might find that some parts of the refrigerator are much colder than others, while other areas are warmer than they should be. If the thermistor is not functioning properly, it might send inaccurate temperature readings, causing the fridge to overcool certain sections and undercool others.

You may notice, for example, that some items freeze while others spoil in the same fridge compartment. This issue is often more noticeable in larger refrigerators or those with multiple compartments and shelves.

How to Test and Diagnose a Bad Thermistor

If you’re noticing any of the symptoms mentioned above, it’s time to test the thermistor and see if it’s the culprit. You don’t need to be an expert to check the thermistor, but you’ll need a multimeter and some basic knowledge of electrical testing.

Here’s how you can go about diagnosing a bad refrigerator thermistor:

Step 1: Unplug the Refrigerator

Before you begin testing the thermistor, make sure to unplug the refrigerator to avoid any risk of electrical shock.

Step 2: Locate the Thermistor

In most refrigerators, the thermistor is located near the evaporator coil or behind a panel in the fridge or freezer. Check your refrigerator’s user manual for the exact location of the thermistor, as this can vary by model.

Step 3: Use a Multimeter

To test the thermistor, set your multimeter to measure resistance (Ohms). Disconnect the thermistor from its wiring, and then place the multimeter probes on each end of the thermistor’s terminals. A working thermistor will show a resistance value that changes with temperature.

If you’re testing the thermistor in a fridge at room temperature, it should have a resistance within the normal range specified in the refrigerator’s manual (often between 10k and 30k ohms). If the resistance is way off or shows no change, the thermistor may be faulty.

Step 4: Check for Continuity

You can also check for continuity, which ensures that the thermistor is not broken. If the multimeter shows continuity (a beep or low resistance), the thermistor is likely still functional. No continuity, or an unusually high reading, means it’s time to replace the thermistor.

Step 5: Replace the Thermistor (If Necessary)

If you find that the thermistor is faulty, you’ll need to replace it. Replacement thermistors can be found at most appliance parts stores or online. When buying a replacement, make sure it’s the correct part for your refrigerator’s make and model.

Replacing the thermistor typically involves disconnecting the old thermistor from its wiring and connecting the new one in its place. Once the new thermistor is installed, reassemble the fridge, plug it back in, and test to see if the temperature issues are resolved.

Frequently Asked Questions

Is it safe to replace the thermistor yourself?

Yes, replacing a thermistor is generally safe as long as you follow proper safety guidelines. Make sure to unplug the refrigerator before starting the work, and if you’re unsure, consider calling a professional.

Can a bad thermistor cause food spoilage?

Yes, if the thermistor is malfunctioning, it can lead to the fridge being too warm or too cold, which can spoil food. If you notice your food going bad quickly or freezing unexpectedly, a bad thermistor could be the problem.

Do I need to replace the thermistor immediately if it’s faulty?

While it’s important to replace a faulty thermistor soon, the fridge might still work with a bad thermistor, but with improper cooling. However, this can lead to further issues, so it’s best to replace it as soon as you can.

Can a bad thermistor cause ice buildup in the fridge?

Yes, a faulty thermistor can cause the cooling system to run too long, leading to ice and frost buildup in the fridge or freezer. This can cause damage to the appliance and food.

Is it expensive to replace a refrigerator thermistor?

Replacing the thermistor itself is relatively inexpensive, usually costing between $10 and $50, depending on your fridge model. However, if you hire a professional for the job, the labor cost may add up.

Can a thermistor cause a refrigerator to stop cooling?

Yes, a bad thermistor can cause the refrigerator to fail to cool properly. If the thermistor isn’t sending the correct temperature data, the fridge may not activate its cooling system as needed.

Is it possible for a refrigerator thermistor to work intermittently?

Yes, sometimes a thermistor may work intermittently before fully failing. If you notice that your fridge’s cooling is inconsistent or if you experience temperature swings, the thermistor could be on the verge of failure.

Do I need a professional to test my refrigerator thermistor?

You don’t need a professional to test the thermistor, as it’s a fairly simple process with a multimeter. However, if you’re unsure about the process, or if the issue persists after testing, it might be a good idea to contact a repair expert.

I hope this article helped you understand how to spot the symptoms of a bad refrigerator thermistor, how to test it, and what steps to take for fixing the issue.