Sudden stoppage of operation refrigeration chamber or, conversely, the continuous hum of the compressor often indicates a failure of one of the key elements of the control system - the thermostat. It is this unit that is responsible for maintaining a given temperature regime, opening and closing the electrical circuit at the right time. When thermostat stops responding correctly to changes in temperature inside the chamber, the products begin to deteriorate, and an ice coat forms on the walls.
Many owners of household appliances Indesit, Atlant or Beko immediately call technicians, not realizing that in most cases the problem can be fixed on your own. Replacing or adjusting this component does not require extensive knowledge of electronics, but demands care and compliance with safety precautions. Understanding the operating principle of the device will help you save a significant amount on service costs.
In this article we will analyze in detail the diagnostic algorithm, methods for checking the serviceability of the part and the step-by-step process of replacing it. You will learn how to distinguish a thermostat breakdown from a compressor malfunction or freon leak. It is critically important to completely disconnect the refrigerator from the power supply before starting any work, since the thermostat is under voltage of 220V.
The design and principle of operation of the thermostat
The thermostat is an electromechanical device that controls the temperature in the refrigerator compartment. The main working element of a classic mechanical regulator is bellows tubefilled with a temperature-sensitive gas (usually freon or chloroform). This tube, often called a capillary, is attached to the evaporator or discharged into the chamber in response to thermal fluctuations.
As the temperature rises, the gas inside the capillary expands, creating pressure on the bellows membrane. This pressure is transmitted to a system of levers, which closes the electrical contacts, starting compressor. When the temperature reaches the lower limit, the gas is compressed, the pressure drops, and the spring opens the contacts, stopping the motor. In electronic models, this function is performed by thermistors that transmit data to the control board.
Modern refrigerators, such as Samsung or LG, are increasingly equipped with electronic sensors, but mechanical thermostats remain the standard for many budget and mid-range models thanks to its reliability. Understanding this difference is necessary for correct diagnosis: mechanics can be “ringed” with a multimeter, and electronics are more often checked by replacement or an oscilloscope.
What is the difference between mechanical and electronic thermostats?
Mechanical thermostats work on the physical expansion of gas and have a characteristic click when turned on/off. Electronic (thermistors) change their electrical resistance depending on temperature and do not make sounds. Mechanical ones are easier to diagnose with a multimeter; electronic ones require knowledge of the resistance ratings for a specific model.
It is important to note that the length of the capillary tube and the number of turns on the evaporator are strictly regulated by the manufacturer. Any damage to the tube or loss of contact with the evaporator will result in incorrect readings. Some models use air thermostatwhere the tube does not come into direct contact with the metal, but measures the temperature of the air in the chamber.
Typical symptoms of a malfunction of the thermostat
You can determine that it is the thermostat that has failed by a number of characteristic signs. Most often, users are faced with a situation where the compressor runs non-stop, trying to “catch up” to a temperature that has in fact already been reached. In this case, the chamber may be too cold, the food freezes, and a thick layer of ice forms on the back wall.
The opposite situation - the compressor is silent, and the refrigerator is warm. If the light is on and the motor is working (checked separately), then the circuit is broken at the contacts of the thermostat. Also, a breakdown is indicated by the absence of a characteristic click when turning the temperature adjustment knob from the extreme position.
Sometimes a “floating” fault occurs when the contacts burn out or stick intermittently. In such cases, the refrigerator may work normally for several days, and then stop freezing or, conversely, freeze the food. Diagnosis of such cases requires a more thorough check of contacts.
The following table helps to differentiate the symptoms:
| Symptom | Probable cause | Action |
|---|---|---|
| The compressor does not turn on, it’s warm in the chamber | Open circuit in the thermostat | Ring the contacts with a multimeter |
| The refrigerator freezes constantly without turning off | Sticking contacts or gas leak | Check the pressure in bellows or replace |
| Short operating cycle (5 minutes running, 5 minutes standing still) | Incorrect calibration or loss of sensitivity | Check the seating of the capillary on the evaporator |
| Ice on food in the fridge compartment | Thermostat does not open the circuit at 0°C | Replacing the thermostat |
It is worth considering that similar symptoms may appear when there is a refrigerant leak or a malfunction of the defrost sensor in the systems No Frost. Therefore, visual inspection and testing are mandatory steps before purchasing a new part.
Diagnostics: how to check a thermostat with a multimeter
To carry out accurate diagnostics, you will need a digital multimeter set to resistance measurement mode (Ohm). Before starting the test, you must ensure access to the thermostat. In most refrigerators, it is located inside the chamber under a plastic cover or in the engine compartment, depending on the model (Stinol, Zanussi etc.).
Remove the adjustment knobs and carefully dismantle the plastic case to get to the electrical contacts. Disconnect the wires from the thermostat terminals. It is important to remember or photograph the connection diagram so as not to confuse the wires during assembly. Usually there are two or three of them (including grounding).
☑️ Multimeter testing algorithm
At room temperature, the contacts of a working mechanical thermostat should be closed (the multimeter beeps, the resistance is close to zero). If the device shows one or infinity, the circuit is broken and the thermostat is faulty. For a complete check, you can place the sensor in a container with cold water (about +5°C) - at this moment you should hear an opening click.
If your model has three contacts, the third is usually responsible for indicating the operation of the compressor or grounding. The test is carried out between the main input contact and the output contact on the compressor. The absence of conductivity in any of the working positions of the handle indicates the need for replacement.
⚠️ Attention: When checking, do not touch the multimeter probes with your hands so as not to introduce an error in the resistance measurements. Also make sure that there are no oxides on the contacts that could distort the result.
In some cases, the contacts may simply be oxidized. If you see carbon deposits, you can try to clean them with fine sandpaper, but this is a temporary measure. It is safer to install a new one thermostat, since the life of mechanical components is limited by the number of operation cycles.
Removing the old thermostat
The process of removing the device depends on the type of installation. In refrigerators with a weeping evaporator, the capillary tube is often fixed in a special channel or pressed with a bar to the rear wall inside the chamber. In models No Frost the sensor may be located behind a plastic panel in the rear of the refrigerator compartment.
Carefully bend the mounting strips or unscrew the screws holding the tube. The main thing here is not to damage the thin capillary. If the tube is pinched or cracked, gas will escape and the new thermostat will immediately fail or not work correctly. Pull the tube through the hole in the chamber wall smoothly, without jerking.
When working with refrigerators of older series, for example ZIL or early models Atlant, it may be necessary to remove the entire top panel. In modern models, access is often organized more ergonomically. Before final removal, check again that all wires are disconnected.
If the capillary tube is glued to the evaporator, do not use force. In some cases, you may need to carefully cut away a layer of insulation or adhesive to free the sensor. When installing a new element, the contact area must be cleaned and degreased for better heat transfer.
⚠️ Attention: It is strictly forbidden to bend the capillary tube at an acute angle or pinch it with tools. This will lead to disruption of the circulation of the working fluid and damage to the device.
Installation and configuration of a new thermostat
Installation of a new element is carried out in the reverse order of dismantling. Make sure you purchase a thermostat with similar specifications. Models may differ in capillary length, temperature response range and contact location. The markings on the body (for example, TAM-133, K-59, RANCO) must match or be a complete analogue.
Fix the capillary tube in its original location using standard clamping strips. The quality of contact between the tube and the evaporator directly affects the accuracy of the work. If the tube dangles in the air, the thermostat will “lie”, reading the temperature of the air, and not the surface of the evaporator, which will lead to incorrect operating cycles.
Connect the wires according to the previously made diagram or photograph. If the color markings of the wires do not match, refer to the diagram of a specific refrigerator. After connecting, assemble the plastic casing and set the adjustment knob to the middle position.
After assembly, turn on the refrigerator. The first cycles of operation may be longer than usual, since the system needs time to stabilize the temperature regime. Do not completely load the chamber with products in the first 2-3 hours of operation.
Common mistakes during self-repair
One of the most common mistakes is ignoring the type of refrigerant and pressure in the system, although this has an indirect effect when replacing the thermostat. More critical is incorrect positioning of the capillary. If you put a sensor from a two-chamber refrigerator into a single-chamber one (or vice versa), the response temperature range will not meet the requirements of the chamber.
They also often forget about the tightness of the hole through which the capillary passes. If warm, moist air enters the chamber, this will lead to abundant formation of condensation and ice around the tube, which will disrupt heat transfer. Use sealant or plasticine to insulate the process hole.
Another mistake is using thermostats with a shorter capillary without extending it. This is physically impossible to do efficiently at home, as it requires welding and vacuuming. It is better to buy a part with a spare length, carefully rolling up the excess.
⚠️ Attention: Do not try to repair the thermostat housing or open the bellows. These are disposable nodes that cannot be restored. Any attempt to interfere will disrupt the calibration of springs and membranes.
Remember that if the problem does not disappear after replacement, it may not be the thermostat. Check the start relay, compressor windings and refrigerant level. Sometimes the “symptoms” of a thermostat failure mask more serious problems with the cooling system.
Is it possible to use a universal thermostat?
There are universal models with adjustable parameters, but setting them up requires special equipment (thermometer, pressure gauge). For a home craftsman, it is safer to buy an original analogue or a complete replacement with a factory setting for a specific refrigerator model.
FAQ: Frequently Asked Questions
Is it possible to temporarily short-circuit the thermostat to make the refrigerator work?
Yes, if you connect the wires going from the network to the compressor (bypassing thermostat), the engine will start and run continuously. This is only permissible as a temporary measure to save food, but requires constant monitoring, since the refrigerator will not turn off and may freeze food or overheat the compressor.
Where can I find the thermostat markings to purchase a replacement?
The markings are applied to the metal body of the device, usually near the exit point of the capillary tube. Look for codes like K-59 L1187, TAM-133 or 17322. You can also find the spare part number in the service documentation for your refrigerator model.
Why doesn’t the new thermostat click?
Electronic thermostats (thermistors) do not make sounds. If you have a mechanical device, the click may be quiet. If there is no click at all and the refrigerator does not turn on, it is possible that a new part is defective or the capillary is installed incorrectly (it does not sense a change in temperature).
How often do you need to change the thermostat?
The service life of a mechanical thermostat is on average 10-15 years or about 30-50 thousand on/off cycles. Scheduled replacement is not required, only if signs of malfunction appear.
Does the temperature in the room affect the operation of the thermostat?
Yes, mechanical thermostats may not work correctly in unheated rooms at temperatures below +10°C...+15°C. For such conditions, there are special climate classes or models with heated thermostat zone.