Modern refrigerators are complex electronic devices, where dozens of sensors are responsible for maintaining the correct microclimate. One of the key elements of the control system is thermistor, often called a temperature sensor. It is this that tells the electronic module when to turn on the compressor and when to stop cooling so that the food does not spoil.
If you notice that your refrigerator Liebherr or Indesit started working intermittently, turns on too often or, conversely, has stopped freezing, there is a problem may lie in this small component. Understanding the principle of its operation will help you diagnose the malfunction yourself and avoid an expensive call to a technician for a simple part replacement.
In this article we will analyze the thermistor device in detail, consider the reasons for its failure and provide step-by-step instructions for checking the resistance. You will learn how to distinguish a working sensor from a burnt one and why sharp change in resistance when heated is the main sign of its performance.
Principle of operation and design of the sensor
The thermistor is a semiconductor resistor whose electrical resistance directly depends on the ambient temperature. Unlike regular resistors, which must remain constant, thermistors are specifically designed to respond to thermal changes. In refrigeration technology, NTC (Negative Temperature Coefficient) thermistors are most often used, the resistance of which decreases as the temperature rises.
The electronic control module supplies a small reference current to the sensor and measures the voltage drop. Based on the data received, the “brain” of the refrigerator makes decisions: start a defrost cycle, turn on the fan or activate the compressor. If the readings fall outside the permissible range, the system may go into error, which will be indicated by a flashing indicator on the panel Samsung or LG.
Structurally, the element is protected by a sealed housing that is resistant to moisture and aggressive environments, since it often operates in conditions of high humidity or direct contact with the refrigerant. Inside the housing is a sensing element made of metal oxides such as manganese, nickel or cobalt, sintered at high temperatures.
⚠️ Attention: Thermistors have different resistance ratings at 25°C (for example, 5 kOhm, 10 kOhm, 50 kOhm). Installing a sensor with an incorrect rating will result in incorrect operation of the entire refrigeration unit.
The accuracy of the readings is critical for energy efficiency. Incorrect data can cause the compressor to wear out, which will significantly reduce the service life of an expensive unit.
Main symptoms of a thermistor malfunction
Diagnostics begins with monitoring the behavior of the refrigerator. When a temperature sensor fails, it often sends false signals or stops transmitting data altogether. This leads to chaotic behavior of the cooling system.
The most common symptom is the continuous operation of the compressor without shutdowns. In this case, the sensor may “think” that the chamber is too warm and require constant cooling. The opposite situation is the complete absence of cold, when the system believes that the temperature has already been reached and does not start the cycle.
It is also worth paying attention to the following manifestations:
- ❄️ Abundant formation of ice or “fur coat” in the refrigerator compartment, even if the door is closed tightly.
- 🔊 Frequent clicks relay and attempts to start the engine, which immediately stop.
- 💡 Flashing of the temperature indicator or display of an error code on the display (for example, F1, E1 or specific codes for Bosch).
- 🌡️ The difference between the actual temperature of the products and the readings on the display is more than 5-7 degrees.
Sometimes the malfunction is of a floating nature. The refrigerator may work normally for several days, and then suddenly stop cooling. This often indicates a broken contact inside the sensor or oxidation of the wires.
It is important not to ignore these signals. Long-term work with a faulty sensor can lead to food spoilage and compressor failure due to overheating.
Where the thermistor is located in different models
The location of the temperature sensor depends on the design of the refrigerator and the manufacturer. In single-chamber models, it is usually located inside the refrigerator compartment, often behind a plastic panel or in a special hole.
In two-chamber systems No Frost sensors can be installed in several places: in the evaporator, in the air duct or directly in the food storage area. In some. models Electrolux access to them is possible only after dismantling the rear wall of the chamber.
Consider typical installation locations:
- 📍 On the back wall of the refrigerator compartment, hidden behind a decorative overlay.
- 📍 Inside a plastic box evaporator (disassembly of the system is required No Frost).
- 📍 In the suction zone of the compressor (to control the temperature of the returning gas).
- 📍 In the air duct between the freezer and refrigerator compartments.
Before starting any work to find the sensor, be sure to disconnect the refrigerator from the power supply. This is a safety rule to violate is not possible, since you will be working with electrical components.
To accurately determine the location in your model, it is best to use technical documentation or disassembly diagrams for a specific brand. Visually, the thermistor often looks like a small “button” or a cylinder on two wires covered with sealant.
Tools for diagnostics and testing
To properly check the thermistor, you will need a minimum set of tools. The main device will be a digital multimeter capable of measuring resistance in the range from 1 kOhm to 100 kOhm.
You will also need:
- 🔧 A set of screwdrivers (phillips and flat) for removing panels.
- 🧊 A container with warm water and a thermometer (to simulate temperature changes).
- 📱 A smartphone with a camera (to photograph the connection of wires before disconnecting).
- ✂️ Pliers or side cutters (in case you need to strip the contacts).
The test is carried out by measuring resistance at different temperatures. First, the resistance is measured at room temperature, then the sensor is placed in water with a known temperature, and the measurements are repeated.
If the multimeter shows “infinity” (open circuit) or “zero” (short circuit) regardless of temperature, the sensor is faulty.
Do not forget that the wires going to the sensor can also be damaged. Before checking the element itself, visually inspect the harness for kinks, traces of rodents or melting.
Step-by-step instructions: how to check the thermistor. multimeter
The diagnostic process requires care and adherence to the sequence of actions. Errors at the measurement stage can lead to incorrect diagnosis and the purchase of unnecessary spare parts.
Follow the steps strictly according to the algorithm:
☑️ Checking the thermistor
- Unplug the refrigerator from the outlet and wait for defrosting if there is a lot of ice in the chamber.
- Remove the necessary panels to gain access to the thermistor connector.
- Carefully disconnect the chip with wires from the electronic module or intermediate harness.
- Switch the multimeter to resistance measurement mode (Ohm, limit 20k or 200k).
- Connect the probes to the contacts of the sensor connector and record the readings.
- Hold the sensor in your hand or lower it into warm water (not higher than 50°C) and watch the numbers change on the screen.
If the resistance changes smoothly and corresponds to the characteristics table, the sensor is working. If the numbers do not change or jump chaotically, replacement is required.
| Temperature (°C) | NTC resistance 10 kOhm (kOhm) | NTC resistance 50 kOhm (kOhm) | Status |
|---|---|---|---|
| 0 | ~33.0 | ~165.0 | Norm |
| 10 | ~20.0 | ~100.0 | Norm |
| 25 | ~10.0 | ~50.0 | Norm (basic) |
| 40 | ~5.5 | ~27.0 | Norm |
| Any | 0 or ∞ | 0 or ∞ | Faulty |
Please note that the values may vary slightly depending on the sensor manufacturer. The main thing here is the very dynamics of reducing resistance when heating.
⚠️ Attention: Do not heat the thermistor with an open fire or a hair dryer at maximum power. Sudden overheating can destroy the internal structure of the semiconductor, even if it was working properly.
After checking, be sure to thoroughly dry the sensor before installation if you used water for testing.
Replacing the sensor and setting up the system
If diagnostics The fault has been confirmed and the thermistor needs to be replaced. Repair of this element is impossible, since it is a monolithic structure. You should buy a new part based on the marking of the old one or the model of the refrigerator.
The replacement process is as follows:
- 🛒 Purchase an analogue with an identical resistance rating (for example, 10 kOhm at 25°C).
- 🔌 Disconnect the old sensor, cutting the wires as close to the body as possible to leave some room for connection.
- 🔗 Connect the wires of the new sensor to the refrigerator wiring using twisting and heat shrink or soldering.
- 🛡️ Carefully insulate the connection point, since the humidity in the refrigerator is high.
- 🔧 Install the sensor in its original place and reassemble the case in the reverse order.
In some modern models Whirlpool or Haier after replacement, you may need to reset the error through the service menu. To do this, use a combination of buttons on the control panel or a special mode described in the instructions.
Is it necessary to reset the error after replacement?
In most cases, the refrigerator itself will detect the new sensor during the next power-on cycle and the error will disappear. However, if the error code is constantly on, try turning off the power to the unit for 15-20 minutes to completely reset the controller memory.
After turning on, let the refrigerator run idle for several hours to make sure the temperature is stable and there are no errors.
Do not skimp on the quality of insulation, since moisture on the contacts will cause corrosion and re-breakage in a short time.
Frequently asked questions and answers (FAQ)
Is it possible to temporarily short-circuit the thermistor to make the refrigerator work?
Technically, this is possible for diagnostics, but is not recommended for continuous use. Shorting simulates high temperature, which will force the compressor to work continuously, leading to freezing of the evaporator and spoilage of food.
Why does the new thermistor not fit?
Sensors can have different wire lengths and housing shapes. The main thing is the electrical characteristics. If the shape does not allow it to be installed properly, you can carefully extend the wires or use heat-resistant sealant to fix it in the seat.
How often should the thermistor be changed?
The service life of the thermistor usually coincides with the service life of the refrigerator (10-15 years). It is not a consumable item and is changed only when a malfunction is detected.
Does defrosting affect the operation of the sensor?
Proper defrosting does not affect it. However, mechanically chipping ice with a knife in the immediate vicinity of the sensor can damage its body or wires, which will lead to breakdown.