A modern refrigerator is a complex electronic mechanism, where not only the compressor and refrigerant, but also a number of electronic components are responsible for maintaining the temperature. Unlike older models, where adjustment was carried out mechanically, today digital sensors are responsible for the accuracy of the readings. If you are wondering what sensors are in the refrigerator, then you should understand: these are the “eyes” and “ears” of the control board, which inform the system about the current state inside the chambers.
Failure of even one element can lead to serious consequences: from food spoilage to defrosting of the entire freezer. Understanding the operating principles of these devices helps you quickly diagnose the problem without calling a technician for basic checks. In this article we will analyze in detail the types of sensors, their location and methods for checking serviceability.
⚠️ Attention: Before carrying out any work on diagnosing or replacing internal components, be sure to disconnect the refrigerator from the power supply. Working with live electronics is dangerous and can lead to a short circuit.
Main temperature sensor and thermostat
The central element of the control system is thermostat or its electronic equivalent - a temperature sensor. It is he who is responsible for turning the compressor on and off depending on the temperature in the main chamber. In older models, this is a mechanical device with a bellows filled with gas that expands or contracts, opening or closing contacts. Modern units use NTC thermistor, the resistance of which varies depending on the heating.
This element is usually located inside the refrigeration chamber, often hidden by a plastic cover on the back wall or built into the control panel. If the sensor “lies” and shows a temperature higher than the real one, the compressor will work continuously, causing severe cold and ice freezing. And vice versa, if the resistance is too high, the equipment may not turn on at all, considering that the norm has already been reached.
Diagnostics of a mechanical thermostat often requires replacing it with a known good one, since testing with a multimeter does not always give an accurate result without changing the temperature. Electronic sensors are tested by measuring resistance at different temperatures. The exact resistance values for your model can be found in the manufacturer's technical documentation.
It is worth noting that in two-chamber models with one compressor often use flon-regulator or a solenoid valve, which is controlled by signals from the main sensor, redirecting cold air to the desired chamber. This creates a complex chain of dependencies where an error in the sensor readings upsets the balance in the entire system.
No Frost and defrost system sensors
In refrigerators with the system No Frost defrost sensors play a critical role. They prevent the formation of an ice coat on the evaporator, which could block air circulation. The main element here is defrost sensor (defrostation). It is installed directly on the evaporator, often in its lower part or mounted in the heating element.
When the ice reaches a certain thickness, the sensor sends a signal to start the heating element. As soon as the ice melts and the evaporator temperature rises, the sensor turns off the heating so as not to overheat the system. If this element fails, two scenarios are possible: either the defrost does not turn on at all, and the refrigerator becomes overgrown with ice, or the heating element works constantly, melting plastic parts.
- ❄️ The defrost sensor usually triggers at a temperature of about -5...-10°C.
- 🔥 The defrost stop sensor opens the circuit at +10...+15°C.
- 🌡️ In some models, these functions are combined in one bimetallic element.
In addition, the system may contain drip receiver overflow sensor. It signals that the water does not have time to evaporate and blocks the start of new defrost cycles or turns on an alarm. This is a rare but possible element in premium models.
⚠️ Attention: The design and number of defrost sensors may vary depending on the manufacturer and year of manufacture of the model. The technical characteristics of the components change, so check the parameters with the official diagram of your device.
Sensors in the freezer and freshness zone
The sensors located in the freezer compartment deserve special attention. Here, the operating conditions are more extreme, so increased demands are placed on the reliability of the components. Freezer temperature sensor ensures maintenance of deep freezing mode. Its readings directly affect the fan rotation speed and compressor operation.
In modern models with the function Smart Cooling or “Fresh Zone” (Zero Zone), additional humidity and temperature sensors can be installed. They create a microclimate ideal for storing vegetables or meat, preventing the food from drying out or freezing. Failure to operate such a sensor will result in the food in the box deteriorating faster than usual.
Often users confuse the symptoms of a sensor failure with a malfunction of the air supply damper. If it is warm in the refrigerator compartment, but normal in the freezer, the problem may not be in the sensor, but in the mechanical damper drive, which is also controlled electronically based on thermometer readings.
Compressor and start relay sensors
The very “heart” of the refrigerator - the compressor - is also equipped with protective elements. Although these are not exactly temperature sensors in the classical sense, they perform a similar condition monitoring function. Thermal relay or thermal protection is built into the compressor housing or start relay. It opens the power circuit if the motor windings overheat above a critical point.
In inverter models the situation is more complicated. There Hall sensors other sensors are used that control the speed of rotation of the shaft and the position of the pistons. They transmit data to the inverter board, which smoothly regulates the power. A malfunction of these sensors leads to the fact that the compressor either does not start or operates with jerks and a strong hum.
Diagnostics of the protective thermal relay is simple: in a cold state it should “ring” (have zero resistance), and when heated, it should open the circuit. If the relay is “broken” and conducts current constantly, the compressor may burn out from overheating, since the protection will not work at the right time.
| Sensor type | Location | Function | Failure symptom |
|---|---|---|---|
| Thermostat / NTC | Refrigerator compartment | Compressor operation control | Not freezing or freezing too much |
| Defrost sensor | Evaporator (No Frost) | Turning on/off the heating element | Ice build-up, "fur coat" |
| Thermal relay | Compressor | Overheat protection | The compressor does not turn on or is humming |
| Damp sensor | Air supply duct | Adjusting the cold flow | Different temperatures in the chambers |
Sensors for inverter control systems
Inverter technology involves abandoning the constant switching on and off of the motor in favor of changing the rotation speed. This requires a constant flow of data. Rotor position sensor inside the compressor tells the control board the current speed. Based on this data, a control pulse is generated.
Also often found in such systems pressure sensor (pressostat), which monitors the refrigerant pressure in the circuit. This allows the system to adapt to conditions: for example, if you put a lot of warm food in the refrigerator, it will suddenly increase power and then go into economy mode. If the pressure sensor is faulty, the system may go into error and stop working to avoid an accident.
Repairing such systems at home is difficult, as it requires special equipment to read error codes from the control board. Often the electronics themselves block the start when receiving conflicting data from the sensors.
☑️ Electronics diagnostics
Diagnostics and signs of malfunction
How to understand that the problem lies in the sensor, and not in a freon leak or compressor failure? The surest sign is incorrect behavior of temperature conditions when the motor appears to be working properly. For example, the refrigerator runs non-stop, but the temperature in the chamber does not drop below +10°C. Or it turns off after 5 minutes, “believing” that the norm has been reached, although it is still warm inside.
To check the electronic sensor (thermistor), you will need a multimeter. It is necessary to remove the sensor, connect the probes and place it in a container with water of a known temperature (you can use a thermometer for control). The resistance should change smoothly as the water temperature changes. A sharp jump or open circuit will indicate a malfunction.
Mechanical thermostats are checked by testing the contacts. In a warm state, the contacts must be closed (or open, depending on the design), and when cooled, they must change their state. If there is no click and the resistance does not change, the part requires replacement.
⚠️ Attention: When replacing sensors, it is important to use components with similar resistance parameters. Installing an unsuitable analogue will lead to incorrect operation of the entire refrigerator, even if the new sensor is working properly.
Sometimes the problem lies not in the sensor itself, but in oxidized contacts or a frayed wire. Carefully inspect the wiring harnesses leading to the doors and evaporator. Frequent opening of doors leads to a break in the cores at the bend.
Frequently asked questions (FAQ)
Is it possible to operate the refrigerator if the defrost sensor is faulty?
Short-term operation is possible, but not recommended. If the sensor is “stuck” in the “off” position, the evaporator will become covered with ice, block the ventilation channels, and the refrigerator will stop freezing. If it is “stuck” when turned on, the heating element will heat up constantly, which can lead to the melting of plastic parts and even a fire.
Why did the refrigerator not work after replacing the sensor?
There may be several reasons. First, the new sensor may have a different resistance that is not suitable for your control board. Secondly, the problem could not be in the sensor, but in the board itself or the compressor. Thirdly, some models require resetting errors through the menu or completely deactivating them for a long time (up to 2 hours) to reboot the controller.
How often do you need to change the sensors in the refrigerator?
Sensors do not have a strict expiration date. They are changed only when they fail. Quality components last 10 years or more. However, under conditions of unstable network voltage or frequent power surges, their service life may decrease. Preventive replacement of serviceable sensors is not required.
Does defrosting affect the operation of sensors?
Proper defrosting does not affect it. However, aggressive defrosting (picking the ice with a knife, using a hair dryer with hot air) can damage the defrost sensor, which is often built into the evaporator. A mechanical shock or overheating can damage the sensitive element instantly.