A modern refrigerator is a complex electromechanical unit, the operation of which is entirely dependent on the accuracy of the readings of various sensors. When a user wonders what the refrigerator temperature sensor is called, he usually means thermistor or thermistor. It is this element that is the “eyes” of the electronic control module, informing it about the current climate inside the chambers.
However, in older models with mechanical control, the role of the controller is played by thermostat, which works on the principle of opening contacts when the specified parameters are reached. Understanding the difference between these devices is critical for correctly diagnosing malfunctions, since the methods for testing them are radically different.
Incorrect operation of the temperature sensor often leads to food spoilage or the formation of excess ice. If you notice that the unit works without stopping or, on the contrary, turns off too often, the problem may lie in this small but important component of the system.
Basic terminology and types of sensors
In technical documentation and among repairmen you can find different names for this device. Most often in modern models it is used NTC thermistor. The abbreviation NTC (Negative Temperature Coefficient) indicates that the resistance of such an element decreases as the temperature increases. This is the most common type of sensor in units with a system No Frost and electronic control.
In older or budget models, it can still be used thermostat (or temperature controller). It is a mechanical device that closes and opens an electrical circuit depending on the expansion or compression of the gas inside the bellows. Unlike a thermistor, a thermostat does not transmit precise digital data to the board, but simply turns the compressor on or off.
Also in complex systems with two compressors or multi-threaded cooling, defrost sensors (defrost sensors) can be found. They often look identical to temperature sensors, but have slightly different calibration characteristics and are responsible for controlling the temperature of the evaporator during the defrost cycle.
⚠️ Attention: When purchasing a spare part, be sure to check the markings. Thermistors marked NTC 5k, NTC 10k or NTC 50k are not interchangeable, as they have different resistance curves.
It is important to distinguish between sensors installed in different areas of the camera. The sensor that monitors the air is usually located at the top of the refrigerator compartment or in a special box. The sensor that monitors the temperature of the evaporator is often hidden behind a plastic panel inside the freezer.
The principle of operation of an electronic thermistor
Electronic thermistor is a semiconductor element whose electrical resistance changes depending on the ambient temperature environment. The control module applies a constant voltage to it and measures the current flowing through the circuit. Based on this data, the processor calculates the current temperature.
Unlike mechanical analogues, the thermistor reacts to the slightest climate changes. This allows the system inverter control to smoothly regulate the compressor power, saving energy and reducing noise levels. The accuracy of such measurements is fractions of a degree.
If the thermistor resistance is outside the permissible range (for example, due to an open or short circuit), an error code may appear on the refrigerator display. Often this is a combination of letters and numbers, for example E1, F1 or flashing indicators, which indicates a malfunction in the sensor circuit.
There are two main types of thermistor characteristics: with negative and positive temperature coefficient. In household refrigeration equipment, s negative coefficientelements are almost universally used. This means that in heat they conduct current better (resistance is lower), and in cold - worse.
Where the sensor is located in different models
The location of the temperature sensor depends on the design of the refrigerator and the brand of the manufacturer. In units with a system No Frost the air temperature sensor is most often located in the upper part of the refrigeration chamber, sometimes in a plastic casing. It can be hidden behind a decorative grille or built into the lampshade.
The evaporator sensor (defroster) in the freezer is usually attached directly to the evaporator fins. To access it, you often need to remove the back wall inside the freezer and remove the plastic panel covering the cooling system. It is usually attached to a latch or clamp.
In models with mechanical control, the thermostat is located inside the fridge compartment. Its capillary tube passes through the wall and is fixed in a special channel of the evaporator or simply pressed against it. The thermostat adjustment knob is moved outside or located inside the chamber.
Secrets of location in popular brands
In LG refrigerators, the sensor is often located in the air duct behind the back wall. At Bosch and Siemens, sensors can be integrated into the fan control unit. Indesit and Ariston often use the classic mount at the top of the chamber.
When searching for a faulty element, it is important to consider that some models may have several thermistors installed: one for the refrigerator, one for the freezer, one for the evaporator and one for the environment. All of them are connected to a single control board via a wiring harness.
Symptoms of a faulty temperature sensor
You can understand that the temperature sensor has failed by indirect signs, without resorting to complex tools. The most obvious symptom is the compressor not working correctly. The unit can work continuously, trying to catch up with the temperature, or, conversely, stand turned off until the food begins to deteriorate.
Another sign is the formation of excess ice or “fur coat” on the back wall, even in systems No Frost. If the defrost sensor “lies” and shows that the evaporator is warm, the defrosting system will not turn on, which will lead to the channel freezing and stopping the circulation of cold air.
Modern refrigerators often themselves report a problem. The “Attention” indicator may light up on the electronic display or an alphanumeric code may appear. The decoding of error codes can be found in the instructions or in the service manual of a specific model.
☑️ Signs of sensor failure
Sometimes a breakdown of the thermistor leads to the fact that the refrigerator stops responding to turns the temperature control knob. In this case, the control module goes into emergency mode and ignores user commands, maintaining average values or working on a timer.
Table of characteristics and error codes
For diagnostics, it is often necessary to know the nominal resistance of the sensor at a certain temperature. Below is a table with approximate values for the most common NTC thermistors used in refrigerators.
| Sensor type | Rating at 25°C | Resistance at 0°C | Resistance at -18°C | Typical error codes |
|---|---|---|---|---|
| NTC 5 kΩ | 5000 Ohm | ~16000 Ohm | ~45000 Ohm | E1, F1 |
| NTC 10 kΩ | 10000 Ohm | ~32000 Ohm | ~90000 Ohm | E2, F2 |
| NTC 50 kΩ | 50000 Ohm | ~160 kOhm | ~450 kOhm | E3, Sensor |
| Thermostat | 0 Ohm (closed) | ∞ (open) | ∞ (open) | None |
It is important to understand that the values in the table are approximate. The exact data depends on the sensor manufacturer (for example, Whirlpool, Samsung, LG use different calibration tables). For accurate diagnostics, it is better to use a working sensor of the same model for comparison.
If the multimeter shows a resistance close to zero (short circuit) or infinity (open), the sensor is clearly faulty and requires replacement. However, values close to normal do not yet guarantee serviceability, since the resistance curve may be disrupted in the middle part of the range.
How to check a sensor with a multimeter
To check, you will need a digital multimeter switched to resistance measurement mode (Ohm). Before starting work, be sure to disconnect the refrigerator from the power supply. Locate the sensor and disconnect its connector from the control board or wiring harness.
Measure the resistance at room temperature. Record your readings. Then place the sensor element in a glass of water and ice (temperature around 0°C). The resistance should change smoothly. If the readings “jump” or do not change at all, the element is faulty.
When checking a mechanical thermostat, the multimeter is set to the “diagnosis” mode. The probes are connected to the contacts. At room temperature the contacts should be closed (beeping). If you place the bellows in the cold, the contacts should open.
⚠️ Attention: Do not attempt to test the sensor while it is connected to the refrigerator control board. Voltage on the board can distort the multimeter readings or damage the measuring device itself.
If you find that the wires going to the sensor are frayed or melted, replacing the sensor itself may not help. First of all, it is necessary to restore the integrity of the wiring using heat-resistant insulation, and only then test the element.
Replacing and calibrating the temperature sensor
The process of replacing the thermistor usually does not require special equipment other than a screwdriver and pliers. After removing the protective panels and disconnecting the old sensor, a new one is installed in its place. It is important to ensure tight contact of the sensor with the surface that it must monitor, sometimes using thermal paste for better heat transfer.
In some models, after replacement, an error reset in the control module memory is required. This is done by disconnecting from the network for a long time (15-30 minutes) or through the service menu. If you do not reset the error, the refrigerator may continue to operate in emergency mode.
Calibration of mechanical thermostats is possible using an adjusting screw, but in domestic conditions it is extremely difficult and requires precise instruments. Most often, mechanical regulators are simply replaced with new analogues with similar markings.
Is thermal paste needed?
When installing the sensor in a metal sleeve or on an aluminum evaporator, it is recommended to use a minimum amount of thermal paste. This will improve the speed of the sensor's response to temperature changes.
Remember that repairing complex electronics yourself may void the warranty. If your refrigerator is under warranty service, it is better to contact an authorized service center to replace faulty components.
Is it possible to temporarily short-circuit the sensor to make the refrigerator work?
Technically, you can short-circuit the thermistor, but this will cause the module to “think” that the chamber is very cold and turn off the compressor. If the chain is broken, the refrigerator may operate in constant freezing mode, which is dangerous for the compressor and food. This is not a solution to the problem.
Why did the new sensor not correct the situation?
There may be several reasons: the sensor rating is incorrectly selected, the problem is not in the sensor, but in the control board or wiring, or there is a freon leak in the system. It is also possible that the new sensor is faulty from the factory.
How often should the temperature sensor be replaced?
The service life of thermistors and thermostats is usually 10-15 years or more. No scheduled replacement required. They are changed only when signs of malfunction appear: malfunctions, error codes or freezing of products.
Does defrosting affect the operation of the sensor?
Proper defrosting does not have a negative effect. However, using sharp objects to chip ice can damage the capillary tube of the thermostat or the thermistor itself, which will lead to their failure.