The refrigerator is the heart of a modern kitchen, ensuring the safety of food and the comfort of household members. However, few people think about what maintains a stable subzero temperature inside this metal box, while there may be heat or cold outside. The key element of this system is thermostat, often called in everyday life simply a thermostat. It is this small device that decides when the compressor needs to turn on to cool the chamber, and when it should stop in order to avoid excessive energy consumption and excessive freezing of food.
The principle of operation of the device is based on the physical properties of substances to change their state under the influence of temperature. When you set the control knob to a certain position, you set a specific threshold at which the electrical circuit opens. Understanding how a thermostat works in a refrigeratorwill help you not only operate the equipment correctly, but also independently diagnose simple breakdowns, saving time and money on calling a technician. In this article, we will analyze in detail the internal structure, operating algorithms and typical problems of this critical unit.
Many users mistakenly believe that a thermostat is just a switch that is triggered by a timer. This is an incorrect statement. In fact, it is a sensitive sensor that reacts solely to thermal changes in the evaporator or air in the refrigerator compartment. If you notice that your Atlant or Indesit started to work incorrectly, the problem often lies in a violation of the calibration or mechanical damage to this element.
Design and principle of operation thermostat
The classic mechanical thermostat is based on a sealed system filled with a temperature-sensitive gas or liquid. This system consists of a bellows (accordion-shaped container) and a long capillary tube, the end of which is fixed to the evaporator or placed in the air flow of the chamber. When the temperature inside the refrigerator rises, the gas in the tube expands, creating pressure on the walls of the bellows. This mechanical movement is transmitted to the contact group, closing the electrical circuit and starting the compressor. The cooling process continues until the temperature drops below the set value. At this moment, the gas is compressed, the pressure drops, and the spring opens the contacts. It is important to note that modern electronic models work differently: there the thermistor plays the role of a sensitive element, changing its resistance, and the signal is processed compressor.
The cooling process continues until the temperature drops below the set value. At this moment, the gas is compressed, the pressure drops, and the spring opens the contacts. It is important to note that modern electronic models work differently: there the thermistor plays the role of a sensitive element, changing its resistance, and processes the signal electronic module control. However, mechanical devices are still widespread due to their reliability and maintainability.
⚠️ Attention: The thermostat capillary tube is made of thin copper and is damaged if handled carelessly. Even a microscopic puncture will cause freon to leak from the sensor, and the thermostat will stop responding to temperature changes, requiring a complete replacement of the unit.
The accuracy of the operation depends on the quality of the calibration of the factory settings and the integrity of the bellows group. If you hear characteristic clicks, this means that the mechanism is working properly through the on and off cycles. In electronic systems, such as No Frost the latest generations, sensors can be located at several points for more precise climate control in different zones.
Why does the gas in the thermostat not evaporate?
The internal cavity of the capillary tube and bellows is filled with an inert gas (often freon or freons) under high pressure during manufacture. Tightness is ensured by special soldering. If the system is sealed, the gas remains inside for decades, ensuring stable operation without the need for refueling.
Types of thermostats: mechanics versus electronics
On the household appliances market, you can find two main types of temperature control devices. Mechanical thermostats, such as the popular models TAM-133 or K-59are manually controlled by turning the handle. They do not require complex electronics and continue to operate even during power surges, making them preferable for regions with unstable power supplies. Their design is simple: a bellows, a spring and contacts in a dielectric housing.
Electronic thermostats are complex units consisting of temperature sensors (thermistors) and a control board. Such systems are often found in premium refrigerators, for example Liebherr or Bosch. They allow you to set the temperature to the nearest degree and are often equipped with a display. Electronics are able to take into account many factors, including the frequency of door opening and ambient temperature, optimizing the operation of the compressor.
- 🔧 Mechanical models are easier and cheaper to repair, since often it is enough to simply replace the entire unit.
- 💻 Electronic systems provide more stable temperatures and smaller differences between cycles on and off.
- ⚡ The electronics are sensitive to power surges and may require reprogramming or replacing the control board.
The choice between types depends on the design of the refrigerator. If your device has a mechanical knob inside the chamber, it most likely has a classic bellows knob installed there. A digital display on the door almost always indicates the presence of an electronic control system. Replacing mechanics with electronics (and vice versa) at home is impossible without a deep redesign of the design and electrical circuit.
Symptoms of a thermostat malfunction
Diagnosing faults begins with observing the behavior of the refrigerator. The most obvious sign of a thermostat failure is a violation of the temperature regime. If the food in the chamber begins to freeze, turning into ice, or, conversely, quickly deteriorates due to insufficient cold, the first thing you should check is this particular unit. Continuous operation of the compressor without rest periods is also an alarming signal.
Sometimes a breakdown manifests itself in the fact that the refrigerator simply stops turning on. In this case, the control circuit does not close and the motor does not receive power. Before sinning on the compressor or start relay, it is necessary to eliminate the possibility of a thermostat failure. A frequent symptom is an operating cycle that is too short: the unit turns on, runs for a couple of minutes and turns off before reaching the desired temperature.
| Symptom | Probable cause | Recommended action |
|---|---|---|
| The refrigerator does not turn on | Broken contacts or gas leak | Ring the contacts, check the handset |
| Continuous operation without stopping | Contacts are stuck or lost tightness | Replacing the thermostat |
| Food freezes | Incorrect calibration or broken spring | Adjusting or replacing the unit |
| Frequent on/off | Incorrect installation of the sensor tube | Check the capillary fastening |
It is worth considering that similar symptoms can be observed when there is a refrigerant leak from the main system or a compressor malfunction. Therefore, a comprehensive diagnosis is mandatory. If, when you turn the control knob, you do not hear a characteristic click, this may indicate that the mechanism is jammed or is completely out of order.
Instructions for replacing the thermostat with your own by hand
Replacing the thermostat is a procedure accessible to a home handyman with basic skills, but requires caution and compliance with safety precautions. Before starting work, be sure to disconnect the refrigerator from the power supply. You will need to remove the top cover (if the regulator is there) or dismantle the inner panel in the refrigerator compartment. In models with No Frost access may be complicated by the need to remove the evaporator.
The most crucial moment is working with the capillary tube. It must be carefully removed from the mounting hole in the evaporator, being careful not to bend or damage it. The new tube is installed at the same depth as the old one. If you are using a universal analogue, make sure that the length of the tube matches the original, otherwise the sensor will read the temperature incorrectly.
☑️ Preparing to replace the thermostat
Electrical wires are disconnected from the old device. It is advisable to first photograph the color markings or number the contacts so as not to confuse them during assembly. The new thermostat is connected strictly according to the same scheme. After installing all components and checking the reliability of the fastenings, you can turn on the unit and monitor its operation for several hours.
⚠️ Attention: When installing a new thermostat, make sure that the capillary tube fits tightly to the surface of the evaporator along the entire length of the contact. Poor thermal contact will lead to delays in the sensor response and incorrect operation of the refrigerator.
Setting and calibrating the temperature mode
After replacement or during operation, it may be necessary to adjust the thermostat. On the body of mechanical models there are often three adjustment screws covered with a seal or varnish. One of them is responsible for the temperature range, the other for the difference between turning on and off (differential). Rotating these screws allows you to fine-tune the operation of the device to specific operating conditions.
For precise adjustments, it is recommended to use an external thermometer placed in a glass of water in the central part of the chamber. By turning the adjusting screw, ensure that the temperature stabilizes in the desired range (usually +2...+4°C for the refrigerator compartment). Remember that changes do not take effect instantly, but after several cycles of compressor operation.
In electronic models, calibration is often done through the service menu or by long-pressing certain buttons on the control panel. Specific combinations depend on the brand and model of the refrigerator. For example, in some models Samsung or LG you need to simultaneously hold down the lock and mode selection buttons.
Frequent questions and operating problems
Users often encounter a situation where the refrigerator clicks but does not start. This may be a sign that the thermostat is signaling to come on, but the start relay or the compressor itself is faulty. However, if there are no clicks at all, the problem is most likely a lack of contact inside the thermostat itself or a break in the supply wires.
Another common problem is freezing of the thermostat tube in the systems No Frost. If the sensor is covered with a layer of ice, it may not be able to read the air temperature correctly, causing defrost or cooling cycles to fail. In such cases, it is necessary to defrost the unit during the day and check the integrity of the tube insulation.
Is it possible to use a universal thermostat instead of the original one?
Yes, in many cases this is possible. Universal models (for example, TAM or K series) have similar characteristics. The main thing is the coincidence of the length of the capillary tube, the diameter of the thread and the electrical parameters of the contacts. Before purchasing, be sure to compare the markings and appearance.
Why does the refrigerator turn on too often?
Frequent starts can be caused by incorrect setting of the thermostat differential, freon leakage from the cooling system, wear of the door seal or overheating of the compressor. Also, the reason may be the installation of a refrigerator next to (battery, stove).
How to check the thermostat with a multimeter?
It is necessary to remove the terminals from the thermostat contacts and put the multimeter in dial mode. At room temperature, the contacts should be closed (the device beeps). If you place the sensitive tube in the cold (for example, in a freezer) for 10-15 minutes, the contacts should open (the beeping will stop).
Understanding the design and operating principles of the thermostat allows you not only to properly service the equipment, but also to extend its service life. Regular checking of seals, timely defrosting and correct temperature conditions are the key to the long life of your refrigerator. If you are faced with a complex malfunction that cannot be eliminated by simply replacing the unit, it is better to turn to professionals.