A modern household refrigerator is a complex unit, the operation of which is based on a precise balance of temperature conditions. Maintaining this balance is based on thermostat (or thermostat), which acts as the main “brains center” of the cooling system, making the decision to turn the compressor on or off. Understanding exactly how this unit functions allows the owner of the equipment to independently diagnose many common breakdowns, without immediately resorting to an expensive call to a technician. If your Indesit or Atlant stops freezing or, conversely, turns food into an ice block, in 80% of cases the problem lies precisely in the temperature control circuit.
Thermostat is an electromechanical or electronic device that responds to changes temperature inside the refrigerator or freezer. Its main task is to open and close the electrical power supply circuit of the compressor depending on the sensor readings. When you hear a characteristic click before starting the engine or after stopping it, it is triggered inside the thermostat. Without this element, the refrigerator would operate continuously, which would lead to rapid wear of the equipment and spoilage of food due to excessive freezing. contact group inside the thermostat. Without this element, the refrigerator would operate continuously, which would lead to rapid wear of the equipment and spoilage of food due to excessive freezing.
It is important to note that despite its apparent simplicity, the principle of operation can differ significantly depending on the type of control. In old models, such as Soviet ZIL or early Biryusa, exclusively mechanical devices were used. Modern units, for example, line Samsung or LG, are increasingly equipped electronic modules, where the role of a thermostat is performed by a sensor (thermistor) and a control board. However, the physics of the process remains unchanged: control of heat and cold.
Physics of the process: how a mechanical thermostat works
The classic mechanical thermostat is based on the properties of gases and liquids to expand when heated and shrink when cooled. The main working element here is a bellows tube filled with freon or a special gas mixture. This tube, often called capillary, is attached to the evaporator or placed in a special tube inside the chamber. When the temperature drops, the gas inside the tube is compressed, creating pressure on the membrane, which, in turn, opens the contacts.
When the temperature in the chamber rises above a predetermined threshold, the gas expands, the pressure on the membrane increases, and the contacts close, starting the compressor. The user regulates this process using a control knob that changes the spring tension. The tighter the spring is, the greater the gas pressure required to open the contacts, which corresponds to a lower temperature in the chamber. This is exactly how the adjustment knob on the panels works Stinol or Pozis.
The design of a mechanical thermostat includes several critical components, each of which performs its own function:
- 🌡️ Sensitive element - a bellows or corrugated tube that responds to changes in gas volume.
- ⚡ Contact group —movable and fixed contacts that pass current to the compressor starting relay.
- 🔧 Adjusting screw —allows the user to set the temperature range (shifts the actuation point).
- ❄️ Capillary tube —connects the bellows to the temperature control zone, transmitting the thermal effect.
⚠️ Attention: Inside the bellows tube there can be not only gas, but also a volatile liquid. If the capillary is mechanically damaged, the substance may escape. Although modern refrigerants are often safe, try not to inhale fumes from a damaged thermostat and ensure the room is ventilated.
The reliability of the mechanical system has been proven for decades, but it has its own life. Over time, the spring may get tired, and the contacts may burn from sparking. In models with single-contact thermostat, when the circuit is opened, the compressor simply turns off. In more complex circuits, for example, in two-chamber refrigerators, a three-contact thermostat is used, which also controls the defrost circuit or signal light.
What is dangerous about a “stuck” thermostat?
If the thermostat contacts are welded in a closed state, the compressor will work without stopping. This will lead to freezing of the evaporator, overload of the engine and eventual failure of the compressor, since it will not have time to cool down during idle cycles.
Electronic thermostats and temperature sensors
Unlike mechanical analogues, electronic control systems do not have moving parts that respond to gas pressure. Here the main role is played thermoresistors (NTC sensors), the resistance of which varies depending on the ambient temperature. The signal from the sensor is sent to the electronic control board, where the microprocessor compares the current readings with those specified by the userby parameters. If the actual temperature is higher than the set one, the board supplies voltage to the starting relay.
Such a system allows you to achieve high accuracy in maintaining temperature, eliminating large differences characteristic of mechanics. Sensors are usually located at several points: in the refrigerator compartment, in the freezer compartment, on the evaporator and even in the freshness zone. This allows the system No Frost to accurately dose the operation of fans and defrost heaters. An error in the readings of even one sensor can lead to incorrect operation of the entire unit.
The advantages of the electronic system are obvious, but there are also maintenance nuances:
- 📉 High accuracy — the error is a fraction of a degree, which is ideal for storing products.
- 🔌 Diagnostics — many modern refrigerators themselves report a sensor malfunction with an error code on the display.
- 💰 Cost - replacing an electronic module or original sensor is more expensive than a mechanical thermostat.
Diagnostics of electronic thermostats requires special equipment. While a mechanic can “ring” it with a multimeter and test it with heat, to test a thermistor it is necessary to measure its resistance at different temperatures and check the data with the characteristics table of a specific manufacturer. For example, sensors Whirlpool and Bosch resistance curves can differ significantly.
Typical symptoms of a thermostat malfunction
You can determine that the thermostat has failed by a number of characteristic signs. Most often, owners are faced with a situation where the refrigerator stops turning off. The compressor hums continuously, trying to reach an unattainable temperature, or, conversely, is silent, although the chamber is already warm. In the first case, the contacts could “stick” in the closed position, in the second, there was a break in the circuit or loss of tightness of the bellows.
Another common symptom is the compressor turning on too rarely or its operation in too short cycles. If you notice that the food in the refrigerator compartment begins to thaw, and the motor turns on only for a couple of minutes every few hours, most likely, the sensitivity of the thermostat has dropped. Mechanical wear of the spring or gas leakage from the capillary leads to the fact that the device “does not feel” a real increase in temperature.
To quickly assess the situation, use the following table of symptoms and probable causes:
| Symptom | Probable cause | Actions |
|---|---|---|
| The refrigerator does not turn on, there is no light | Open circuit of the thermostat or lack of power | Check the patency of the contacts with a multimeter |
| The compressor runs without stopping | Contacts sticking or freon leaking from the capillary | Replacing the thermostat or searching for a refrigerant leak |
| The chamber is too cold (ice on the food) | Settings are lost or short circuit in the circuit | Try adjustment, check the sensor |
| Frequent on/off (clocking) | Incorrect operation of the thermostat or a problem with the start relay | Diagnostics of the duration of operating cycles |
Diagnostics and checking the thermostat with a multimeter
Before buying a new part, you need to make sure that the old one is faulty. For mechanical thermostats, there is a simple and reliable "heat" test method. First you need to dismantle the device by disconnecting the refrigerator from the network. Then the thermostat contacts are tested with a multimeter in resistance measurement mode. If the device shows “infinity” (break), and the regulator knob is at maximum cold, this is the first sign of a malfunction.
For a more accurate check, you can place the sensitive part of the thermostat (capillary) in a container with water at room temperature (about +20°C) for several minutes. After this, call your contacts again. A working thermostat designed to operate in a refrigerator compartment should have contacts that open when heated. If they remain closed even in warm water, the device is faulty and requires replacement. In the case of electronic sensors, resistance is measured, which should drop when heated.
When carrying out work, follow the following safety rules:
- 🔌 De-energizing —always remove the plug from the socket before starting any work.
- 🧤 Hand protection —use gloves if work with sharp metal edges inside the chamber.
- 📏 Accuracy —do not bend the capillary tube of the mechanical thermostat, it breaks easily.
⚠️ Attention: When installing a new one For a mechanical thermostat, it is important to position the capillary tube correctly. It should fit tightly to the evaporator or fit into the standard seat. If the tube hangs in the air, the temperature readings will be incorrect and the refrigerator will not reach the desired mode.
Replacing the thermostat: step-by-step instructions
The replacement process begins with finding the thermostat itself. In most models, it is hidden under a plastic cover inside the refrigerator compartment, often next to the light bulb or temperature control. In some cases, for example, in refrigerators Indesit with a crying evaporator, the thermostat may be located outside, near the compressor. It is necessary to remove the regulator handle, unscrew the mounting screws and carefully remove the housing.
The next step is to disconnect the wires. Before disconnecting, it is recommended to take a photo of the connection diagram or mark the wires with a marker so as not to confuse them during assembly. Pay special attention to grounding: if there was a ground wire on the thermostat body, it must be connected to the new device. After installing the new thermostat, the capillary is carefully laid along the standard path, without sharp creases.
☑️ Algorithm for replacing the thermostat
After assembling and connecting the refrigerator to the network, do not expect instant results. The unit will take time (from 2 to 6 hours) to reach temperature and make the first shutdown cycle. During this period, do not open the door frequently and do not load the chamber with food to allow the system to return to normal.
Nuances of setup and calibration
Many users wonder: is it possible to adjust the thermostat more accurately? Mechanical models often have an adjustment screw hidden under a seal or plastic plug. Turning this screw changes the response range. However, it is not recommended to do this without a special thermometer and experience. Shifting the trigger point even by half a turn can change the temperature in the chamber by 3-5 degrees.
In electronic systems, calibration is often carried out through the service menu, access to which is protected by a combination of buttons. Manufacturers do not recommend users to tamper with the factory settings, as this may disrupt the system operation algorithms No Frost or lead to incorrect operation of the freshness zone. If the refrigerator freezes but does not turn off, most often the problem is not in the settings, but in a freon leak or a malfunction of the sensor itself.
Is it possible to temporarily operate a refrigerator with a faulty thermostat?
Theoretically, it is possible if you connect the wires directly so that the compressor works constantly. However, this requires constant manual control: you will have to turn off the refrigerator from the outlet yourself when the temperature reaches normal, and turn it on again when it rises. This is inconvenient and risky for a compressor that is not designed to operate without rest cycles.
Why did the refrigerator start working longer after replacing the thermostat?
The new thermostat may have slightly different response characteristics. In addition, if during replacement the capillary tube was not pressed tightly enough to the evaporator, the sensor will “see” the temperature more slowly. Give the refrigerator 12-24 hours to stabilize modes.
What is the difference between a refrigerator thermostat and a freezer thermostat?
They differ in the operating temperature range. The freezer (tambour) thermostat is set to lower values (down to -24°C and below), while for the refrigerator the range is usually from 0 to +10°C. Installing the wrong type will lead to incorrect operation.
How to understand that the problem is not in the thermostat, but in the compressor?
If, when the thermostat contacts are closed (direct voltage supply), the compressor does not start, but only hums or is silent, the problem is in the start relay, the motor itself or the power circuit. If the compressor works, but there is no cold, there may be a freon leak or a clogged capillary in the system, and the thermostat has nothing to do with it, it is just trying to start the motor.
Does it need to defrost the refrigerator before replacing the thermostat?
Full defrosting is not necessary if access to the thermostat is in the upper part of the chamber. However, if the work involves manipulating the back wall or the evaporator, where there may be ice, it is better to defrost the unit so that water does not get on the electrical contacts.