The refrigerator is an integral part modern kitchen, ensuring the safety of food for a long time. However, many owners do not even think about what complex mechanisms are hidden behind the usual door, allowing them to maintain a stable temperature. One of the key parts in this system is thermostatwhich is often called the "brain" of climate control inside the chamber.
It is this small device that is responsible for the timely turning on and off of the compressor, preventing either excessive cooling or defrosting of the contents. Understanding how the refrigerator thermostat workswill help you not only gain a deeper understanding of technology, but also independently diagnose a number of common malfunctions. In this article, we will take a detailed look at the internal structure of the regulator, the types of sensors and the nuances of their operation.
A malfunction of this element often leads to the unit starting to work continuously or, conversely, not starting at all. Knowledge of the operating principles thermostat will allow you to save time on calling a technician in simple cases or correctly describe the problem to a specialist. Let's figure out what's going on inside this device.
The main purpose and principle of operation of the regulator
The main task of the thermostat is to automatically maintain the user-specified temperature inside the refrigerator or freezer. It works like an electrical switch, opening and closing the compressor power circuit depending on the sensor readings. When the temperature in the chamber rises above the set threshold, the contacts close, starting the motor. When the desired cold is reached, the circuit opens and the compressor stops.
The operation of most mechanical thermostats is based on the physical property of gases and liquids to change their pressure when the temperature changes. A sensitive element filled with refrigerant reacts to thermal fluctuations. The phase transition point of the working substance inside the bellows is a critical parameter that determines the minimum achievable temperature of the evaporator. This pressure is transmitted to the membrane, which mechanically acts on the contacts.
Modern electronic models use semiconductor elements whose resistance changes depending on heating. The electronic control unit reads these changes and issues a command to start the compressor. This approach allows you to achieve higher accuracy, up to tenths of a degree, which is especially important for expensive models with a system thermistors - semiconductor elements whose resistance changes depending on heating. The electronic control unit reads these changes and issues a command to start the compressor. This approach allows you to achieve higher accuracy, up to tenths of a degree, which is especially important for expensive models with a system No Frost.
It is important to understand that the thermostat does not create cold, but only controls the cooling system. If you hear a click before the engine starts, this is the operation of this particular mechanism. Without a working regulator, the refrigerator will either turn into a block of ice or become a useless storage box.
Design of a mechanical thermostat
A classic mechanical thermostat is a sealed case, inside which the main working components are located. The design is quite reliable, which explains the long service life of many older refrigerators. The main elements are a bellows (corrugated metal container) filled with freon or other gas-liquid substance, and a system of levers.
The bellows is connected to a long capillary tube, the end of which is attached to the evaporator or placed in a special tube inside the chamber. When the temperature changes, the volume of gas in the tube changes, which leads to deformation of the bellows. This movement is transmitted to the moving contact. The temperature is adjusted by the user through a handle that changes the tension of the spring that counteracts the pressure of the bellows.
Inside the case there is also contact groupwhich directly switches the electric current. The contacts must be made of materials that are resistant to sparking, since the circuit opens regularly under load. Some models have a “quick pass” mechanism through the switching point to avoid contact rattling and extend their service life.
⚠️ Attention: Mechanical thermostats are sensitive to vibrations. Frequent slamming of the door or placing the refrigerator on an uneven floor can lead to misalignment of settings or rattling of contacts, which reduces the life of the device.
The tightness of the capillary tube and bellows is a critical parameter. If a microcrack occurs in the system and the gas evaporates, the thermostat will stop responding to temperature changes. In most cases, it is impossible to repair such a leak; a complete replacement of the unit is required.
Electronic temperature sensors: features and advantages
With the development of technology, compact electronic sensors have replaced bulky mechanical devices. They are based on thermistors, which change their electrical resistance when the ambient temperature changes. This allows you to transfer accurate data to the main control board of the refrigerator.
The main advantage of electronic systems is the ability to implement complex control algorithms. The board can take into account not only the current temperature, but also the operating time of the compressor, the frequency of door openings and even the external temperature in the room. This ensures more economical energy consumption and stable temperature conditions.
Electronic thermal sensors are often installed at several points: in the refrigerator compartment, in the freezer, in the freshness zone and even at the outlet of the evaporator. Such a distributed network of sensors allows the system No Frost to accurately dose defrost and prevent the formation of ice. Data from the sensors is processed by a microprocessor in real time.
However, electronic systems also have their drawbacks. They are more sensitive to power surges. While a mechanical thermostat can survive a power surge, the electronics often fail, requiring replacement of not only the sensor, but also the control board. In addition, diagnosing electronic faults requires special equipment.
Comparison of mechanical and electronic control systems
The choice between mechanics and electronics often becomes a matter of preference and budget. Mechanical systems are easier and cheaper to repair, while electronic systems provide greater comfort and functionality. Understanding the difference will help you correctly assess the capabilities of your equipment.
Below is a table comparing the main characteristics of both types of thermostats, which will help systematize knowledge about their design:
| Characteristics | Mechanical thermostat | Electronic sensor |
|---|---|---|
| Principle of operation | Change in gas/liquid pressure | Change in electrical resistance |
| Adjustment accuracy | Low (2-3°C) | High (0.5-1°C) |
| Difficulty of repair | Low (assembly replacement) | High (board diagnostics required) |
| Cost of spare parts | Available | High |
| Resistance to current surges | High | Low |
Mechanical regulators often have a characteristic click when switching, which can be heard even from the next room. Electronic systems operate almost silently, since relay switching can be placed in a separate unit or use solid-state elements. This affects the overall acoustic comfort when operating the refrigerator.
It is worth noting that in modern mid- and high-class models, mechanics are becoming less and less common. Manufacturers are striving to introduce “smart” systems that can be connected to a smartphone and remotely monitor the status of products. However, in the budget segment and in refrigerators of simple design mechanical thermostats still occupy a dominant position.
Diagnostics of thermostat faults
You can determine that the thermostat is out of order by a number of indirect signs. The most obvious symptom is that the refrigerator has stopped turning off and is running around the clock, or the compressor does not start at all, although there is voltage in the network. In the first case, the products may freeze, in the second, they may deteriorate from the heat.
For the initial check of a mechanical thermostat, you can use the freezing method. It is necessary to unplug the refrigerator, defrost it, and then place the sensitive thermostat tube in the freezer for several hours. If after this, when connected to the network, the compressor does not start (provided that the start relay is working properly), then the thermostat does not close the contacts and requires replacement.
You can also check the device using a multimeter in dial mode. At room temperature, the contacts should be closed (if it is a refrigerator thermostat). If the device shows a break, it means that the internal spring has burst or the contacts have burnt. In electronic models, the test is performed by measuring the resistance of the sensor and comparing it with a table of ratings for a specific temperature.
A frequent problem is not a complete breakdown, but “runaway” calibration. In this case, the refrigerator operates, but the temperatures do not correspond to the positions of the adjustment knob. For example, at minimum it freezes as well as at maximum. This often happens when the bellows is deformed or the spring is weakened.
Replacing and adjusting the thermostat
The process of replacing the thermostat requires care and compliance with safety precautions. Before starting any work, you must completely disconnect the refrigerator from the power supply. Dismantling usually begins with removing the protective panels and the regulator handle. It is important not to damage the capillary tube, as it is very thin and can easily be cut.
When installing a new thermostat, it is necessary to secure the sensitive tube in the same place and with the same force as the old one. Incorrect contact with the evaporator will result in incorrect readings. For fixation, special clamps or thermal conductive paste are often used to improve heat transfer.
- 🔧 Unplug the refrigerator and defrost the chambers.
- 🔧 Remove the temperature control knob and decorative trims.
- 🔧 Disconnect the wires, having previously memorized them location.
- 🔧 Carefully remove the old thermostat, freeing the capillary tube.
- 🔧 Install the new device, secure the tube and connect the wires.
After replacement, adjustment may be required. For mechanical models there is often an adjustment screw under the seal that allows you to adjust the temperature range. However, you shouldn’t go there without special equipment and knowledge - it’s better to entrust it to a professional. Electronic models are often calibrated automatically or through the service menu.
⚠️ Warning: Do not attempt to extend the thermostat capillary tube or use sealants to repair it. A violation of the tightness or a change in the volume of the system will lead to complete inoperability of the device.
☑️ Check before starting
Frequently asked questions about the design of thermostats
There are many myths around thermostats. For example, there is an opinion that if the refrigerator does not freeze well, then you just need to “turn the knob to the maximum.” In fact, if the thermostat is working properly, it will provide the desired temperature itself. Twisting the knob only changes the shutdown threshold, forcing the compressor to work longer, which can lead to overheating if the problem is not in the settings.
Another common question: is it possible to replace a mechanical thermostat with an electronic one? Theoretically it is possible, but this requires a deep rework of the control system, laying new wires and programming the board. In 99% of cases, such an upgrade is not economically feasible and it is easier to buy a new refrigerator.
Why does the thermostat click?
The click is the sound of instantaneous switching of contacts. In mechanics, this occurs thanks to a spring mechanism that sharply brings or separates the contacts to avoid arcing. In electronics, the relay that controls the compressor may click.
Also, users often confuse a thermostat with a defrost sensor. These are different devices. The thermostat controls the cooling, and the defrost sensor monitors the evaporator temperature in defrost mode, turning off the heating element when the ice melts. If one of them fails, the entire operating cycle of the refrigerator is disrupted.
Understanding the design of the thermostat helps you take better care of your equipment. Do not jerk the adjustment knob sharply, do not hit the housing in the area where the sensor is installed, and keep the capacitor clean so that the system operates in the designed mode. This will extend the life of the entire unit.
Is it possible to repair a mechanical thermostat yourself?
At home, repairing a mechanical thermostat is practically impossible and impractical. The device requires sealed gas charging and precise spring calibration at the factory. An attempt to open it will lead to a violation of the tightness and final failure. The only way out is to replace it with a new analogue.
Why does the refrigerator turn on immediately after turning it off?
This may indicate a malfunction of the thermostat, which does not open the contacts when the desired temperature is reached, or a refrigerant leak, which is why the temperature in the chamber does not drop to the shutdown threshold. Loss of elasticity of the bellows is also possible.
Does the temperature in the room affect the operation of the thermostat?
Yes, mechanical thermostats may not work correctly at very low ambient temperatures (below +10°C), since the temperature difference between the chamber and the room becomes insufficient for the bellows to operate correctly. To work in a cold room, you need special models with one compressor or a “single compressor” system.
How often do you need to change the thermostat?
The service life of the thermostat usually coincides with the service life of the refrigerator itself (10-15 years). No scheduled replacement required. They change it only when signs of malfunction appear: constant operation, lack of cold or incorrect temperature.