Modern refrigerators have ceased to be simple metal boxes with a freezer, turning into complex electronic systems, where each element plays a key role in maintaining food freshness. The heart of this climate control system is a small but critical component that constantly monitors temperature changes inside the chambers. It is thanks to this sensor that the compressor “knows” when it needs to turn on for cooling, and when it can rest, saving energy. thermistor, which constantly monitors temperature changes inside the chambers. It is thanks to this sensor that the compressor “knows” when it needs to turn on for cooling, and when it can rest, saving energy.
If you notice that your Indesit or LG started to work in emergency mode, is constantly humming, or, conversely, has stopped freezing, the problem is often lies precisely in the distortion of the temperature sensor readings. Understanding the operating principle of this element will help you avoid unnecessary expenses on calling a technician for simple diagnostics, which can be done independently if you have basic tools.
In this article we will analyze in detail how the thermistor works, how it differs from the old mechanical thermostat, and also provide a step-by-step algorithm for checking its performance using a multimeter. You will learn why even a seemingly serviceable sensor can produce incorrect data and how to correctly interpret the results of resistance measurements.
Principle of operation and difference from a thermostat
A thermistor is a semiconductor resistor, whose electrical resistance directly depends on the ambient temperature. Unlike mechanical thermostats, which open the circuit when a certain point is reached, the thermistor works in conjunction with electronic control module. It continuously sends signals about the current thermal background, allowing the system to precisely regulate the compressor power.
Most modern refrigerators, including models Bosch i Samsung, use negative temperature coefficient (NTC) thermistors. This means that when the temperature decreases, their resistance increases, and when heated, it decreases. This characteristic allows the electronic “brain” of the refrigerator to determine with high accuracy the moment when the cooling circuit is turned on and off.
The main advantage of the electronic system over the mechanical system is the ability to maintain the temperature regime with an accuracy of a degree, which cannot be achieved using the old bimetallic thermostat. However, this technology also has vulnerabilities: sensitivity to power surges in the network and oxidation of contacts at the points of connection with wires.
⚠️ Attention: When working with refrigerator electronics, always disconnect the device from the power supply. An attempt to ring the thermistor under voltage is guaranteed to lead to the burning of the electronic control module.
Structurally, the sensor is made in the form of a small plastic or metal tip, inside of which there is a sensitive element filled with sealant to protect against moisture. The critical parameter is not only the serviceability of the element itself, but also the integrity of the insulation of the wires suitable for it, since moisture on the contacts causes false readings.
Main signs of a malfunction of the temperature sensor
Diagnostics of any unit begins with an analysis of the symptoms exhibited by household appliances. When thermistor fails or starts to “lie”, the refrigerator behaves inappropriately. The electronic module receives incorrect data and issues commands that do not correspond to the real situation in the chambers.
The most common symptom is continuous operation of the compressor. If the sensor “thinks” the chamber is too warm, it will keep the compressor on until the food turns to ice or until the system goes into an overload error. Otherwise, if the sensor shows that there is already cold, the refrigerator may not turn on at all.
Modern models with displays often signal a problem with error codes. For example, this may be an “Er FF” error or a flashing temperature indicator, and this may be a flashing “Alarm” indicator. However, you cannot rely only on codes, as they may indicate other problems in the system. LG this may be an “Er FF” error or a flashing temperature indicator, and Electrolux — flashing of the “Alarm” indicator. However, you cannot rely on the codes alone, as they may indicate other problems with the system.
- 🧊 Products in the main chamber freeze, although the regulator is set to minimum.
- 🔊 The compressor works without interruption, trying to gain non-existent cold.
- 🌡️ Temperature in the chambers fluctuates (floats) with a large amplitude.
- 💡 The emergency temperature indicator lights up on the control panel.
Sometimes the malfunction does not appear immediately, but is of a floating nature. A sensor may work fine at one temperature but fail at another. This often happens when contact is broken inside the element or a microcrack has formed, which either closes or opens due to vibration or thermal expansion.
The location of the sensors in different models
The number and location of thermistors depends on the type of refrigerator and the number of cooling circuits. In simple models with one compressor and system No Frost there are usually two main sensors: one in the evaporator and one in the air flow of the main chamber. In more complex two-compressor models, their number can reach four or more.
The evaporator sensor is usually hidden behind a plastic panel inside the freezer or behind the back wall in the case of a system No Frost. It is necessary to control the defrosting process and prevent the radiator from freezing. It is often the most difficult to get to, as it requires partial disassembly of the interior.
The air flow sensor (chamber) is most often located on the back wall of the refrigerator compartment or built into one of the plastic air ducts. In some models Indesit i Atlant it can be hidden in a decorative trim on the side wall. To access it, sometimes it is enough to simply remove the shelf without resorting to complex dismantling.
Hidden arrangement in two-chamber models
In refrigerators with a freshness zone (zero chamber), a third, separate thermistor is often installed, which controls the temperature in this particular compartment. Its malfunction will lead to the fact that the meat and fish in the “nulevik” will either dry out or become covered, while in the main chamber everything will be fine.
It is important to understand that in systems with full No Frost sensors can be additionally installed in the fan area or in the air supply duct. This allows the system to balance the flow of cold air between the freezer and refrigerator compartments by opening and closing special dampers.
Step-by-step instructions for checking with a multimeter
To carry out an accurate diagnosis, you will need a digital multimeter set to resistance measurement mode (Ohm). Before starting work, the refrigerator must be completely defrosted and unplugged for at least 2 hours so that the temperature of the sensors is equal to room temperature.
The first step is to gain access to the sensor itself. Remove the plastic cover or panel hiding the thermistor. Carefully disconnect the connector from the sensor to the wiring harness. If the connector is located in a hard-to-reach place, you may have to disconnect the entire harness from the control board, first photographing the position of the contacts.
Connect the multimeter probes to the contacts of the sensor connector. Polarity in this case does not matter, since we are measuring active resistance. Record the readings on the device screen. For room temperature (about 20-25°C), a working thermistor usually shows a resistance in the range from 4 to 10 kOhm, but the exact values depend on the model.
☑️ Checklist before checking
The most reliable way to check is the “heating method”. Leave the probes connected to the sensor and pinch the thermistor body tightly between your fingers. Your body heat (around 36°C) will cause the resistance of the NTC thermistor to begin to drop. If the numbers on the multimeter screen react quickly and creep down, the sensor is working. If the readings stand still or fluctuate chaotically, the element requires replacement.
| Environment temperature | Expected resistance (approximate) | Response of a working NTC |
|---|---|---|
| +25°C (Room) | 5.0 - 7.0 kOhm | Stable value |
| +36°C (Warm hands) | 3.0 – 4.5 kOhm | Smooth decrease |
| 0°C (Ice boundary) | 15.0 – 20.0 kOhm | Increase in resistance |
| -18°C (Freezer) | 40.0 – 60.0 kOhm | High resistance |
Replacement process and setting up the system
If the diagnostics showed that the thermistor is faulty, it must be replaced. You should buy an analogue with exactly the same characteristics, since different manufacturers use sensors with different resistance curves. Installing an unsuitable sensor will lead to incorrect operation of the refrigerator, even if it physically fits into place.
To replace, carefully remove the old sensor from the mounting socket. Usually it is simply removed or snapped off. The new element is installed in the same position. Pay special attention to connecting the wires: the twists must be carefully soldered and insulated with heat shrink, since there is high humidity in the chamber, and ordinary electrical tape will quickly become unusable.
After installing the new component, reassemble the refrigerator in the reverse order. Connect the device to the network. In most cases electronic module automatically recognizes the new sensor and resets the error. However, in some models Samsung or Whirlpool it may be necessary to force errors through the service menu.
⚠️ Attention: Do not use ordinary PVC electrical tape to insulate connections inside the refrigerator. In the cold, it hardens and peels off, which will lead to oxidation of the contacts and repeated failure. Use only high-quality heat shrink.
Frequently asked questions and final recommendations
Completing the review, it is worth noting that the thermistor is a consumable item, the resource of which is limited. Even if your refrigerator is working properly, after 7-10 years of operation you should be prepared to diagnose this system. Preventative replacement of sensors during major repairs of equipment often extends the life of the compressor.
Do not ignore the first signs of unstable operation. Leaving the compressor idle for a long time due to a faulty sensor can lead to overheating and costly repairs or replacement. Timely diagnostics costs pennies compared to replacing the motor.
Remember that electronics are sensitive to voltage quality. If your network has frequent surges, it is recommended to use a stabilizer or at least a high-quality voltage control relay to protect the expensive control module and sensors.
Is it possible to temporarily short-circuit the thermistor to make the refrigerator work?
It is strictly not recommended. Shorting or opening the sensor circuit will cause the control module to go into emergency mode or the compressor will work constantly, which can cause food to defrost or the evaporator to freeze in a couple of hours.
Why does the new sensor show a different resistance than the old one?
The resistance of the thermistor is highly dependent on temperature. If the old sensor was warm and you just took the new one out of the box (or vice versa), their readings will be different. They need to be compared only at the same temperature.
How often do you need to change the thermistor in the refrigerator?
The service life of the thermistor is usually 7-10 years. No scheduled replacement is required; it needs to be changed only when symptoms of a malfunction appear or the breakdown is confirmed by diagnostics.
Does the type of refrigerant affect the operation of the thermistor?
No, the thermistor measures the temperature of the air or surface, not the properties of the gas. The type of freon (R600a or R134a) does not affect the choice or operation of the temperature sensor.