A sudden stop of the compressor or, conversely, endless operation of the motor often indicates a failure of the control system temperature. In most household refrigerators, whether classic Atlant or modern Bosch, a thermostat is responsible for this process. This small mechanical or electronic device constantly monitors the temperature inside the chambers and sends a signal to turn the engine on or off.
If you notice that the food in the refrigerator compartment has begun to become covered with an ice crust or, on the contrary, is quickly deteriorating due to insufficient cooling, you cannot ignore the problem. Timely thermostat diagnostics avoids expensive compressor repairs or complete replacement of the unit. In this article we will analyze in detail the testing algorithm, the necessary tools and typical repair mistakes.
Before starting disassembly, it is important to understand the principle of operation of the unit. The thermostat closes and opens the electrical circuit depending on the readings of the sensing element. Understanding this mechanism will help you correctly interpret the measurement results and make the right decision about replacing the part.
The operating principle and main functions of the thermostat
The thermostat is an electromechanical relay that controls the operation of the compressor. Inside the device there is a sealed tube (bellows) filled with freon or inert gas. This tube, called capillary, is fixed to the evaporator or freely located in the chamber. When the temperature changes, the gas inside the tube expands or contracts, affecting the membrane, which, in turn, opens or closes the contacts.
Electronic models, often found in technology Liebherr or Siemens, use thermistors. They have no moving parts or gas tubes, and the resistance changes depending on the heat. However, mechanical thermostats remain the most common due to their reliability and low cost. Their task is to maintain a given temperature regime, ensuring the cyclic operation of the refrigeration unit.
Failure of this element leads to a disruption of the cycle. If the contacts are “stuck” in the closed position, the compressor will work non-stop, trying to cool the chamber to impossible temperatures. If the circuit is open forever, the motor simply will not start, and the temperature in the chamber will begin to rise. Understanding exactly how your refrigerator behaves is the first step to identifying the problem.
⚠️ Attention: Before any manipulations with the electrical components of the refrigerator, be sure to disconnect the device from the power supply. Working under voltage is dangerous to life and can lead to a short circuit.
Why do thermostats fail?
Mechanical thermostats often break due to degradation of the bellows (gas leak) or oxidation of the contacts. Electronic sensors may suffer from power surges or moisture on the control board. Also, the cause may be physical damage to the capillary tube due to careless defrosting or cleaning of the chambers.
Clear signs of a malfunction of the thermostat
It is possible to determine that the problem lies in the thermostat by a number of indirect signs. However, it is worth remembering that similar symptoms can be observed when there is a freon leak or a faulty start relay. Therefore, a comprehensive assessment of the situation is extremely important for correct defection.
Here are the main symptoms indicating the need to check the regulator:
- 🧊 The compressor works continuously, without turning off for hours, and a thick coat of ice forms on the back wall of the chamber.
- 🔇 The refrigerator is silent: the motor hums or clicks, but does not start, while the chamber is warm and the light is on.
- ❄️ The temperature in the refrigerator compartment does not correspond to the set values (too cold or too warm) with a working seal.
- 💡 The light inside is on, but the engine operating cycle is broken (pauses are too short or too long).
Particular attention should be paid to models with one compressor and system No Frost. In such units, malfunction of the thermostat can lead to defrosting of the evaporator and subsequent failure of the defrost heating element or fan. If you hear clicks, but it does not turn on, it is possible that the contacts inside the regulator are simply burnt out and do not conduct current.
Preparation for diagnostics: tools and safety
To conduct a quality check, you will need a minimum set of tools. The main device will be a multimeter (tester), which allows you to ring the circuit for an open or short circuit. You may also need screwdrivers to remove the covers and, in some cases, pliers.
The preparation process includes several critical steps that cannot be ignored. The safety and security of equipment depend on proper preparation of the workplace.
☑️ Preparation for checking the thermostat
It is important to determine the location of the thermostat in advance. In most models, it is located inside the refrigerator compartment under a plastic cover, next to the temperature control knob. In some cases, for example, in refrigerators Indesit or Stinol, it may be hidden behind the control panel on top. Read the instructions for your model if you cannot visually find the unit.
Before starting work, be sure to defrost the chamber if there is a lot of ice in it. Moisture can get on the multimeter's contacts or inside electrical connections, causing the readings to change or cause an accident. Allow the equipment to dry completely if defrosting was carried out.
Visual inspection and initial check
The first stage of diagnosis is a careful visual inspection. After removing the protective panel, evaluate the condition of the contacts and the thermostat body itself. There should be no traces of burning, plastic melting or metal oxidation on the surface. If you see black spots around the terminals, this is a sure sign that the contacts have sparked and require replacement.
Pay attention to the fastening of the capillary tube. It must fit snugly against the evaporator or be properly fixed in the chamber. If the tube has jumped out of its seat, the thermostat will “lie” about the temperature, believing that the chamber is warmer than it actually is. In such cases, repair may not consist of replacement, but of correct installation of the sensitive element.
Check the integrity of the wires going to the device. It often happens that the insulation rubs against the metal edges of the housing, which leads to a short circuit or open circuit. If no visual defects are detected, we proceed to an instrumental test using a multimeter.
⚠️ Attention: Never try to check the thermostat under voltage by simply touching the wires with probes. This may damage the multimeter. All resistance and continuity measurements are carried out only on a completely de-energized device.
Diagnostics with a multimeter: step-by-step instructions
The most reliable way to check a refrigerator thermostat is to use a multimeter in resistance (Ohm) or continuity measurement mode. To do this, you need to remove the thermostat by disconnecting the wires (after remembering their location). Typically, three or four wires are suitable for a mechanical thermostat.
Here is the algorithm for checking:
- Set the multimeter to continuity or resistance measurement mode.
- Identify the input and output contacts. In mechanical models, these are usually contacts to which wires from the network and from the compressor fit.
- Touch the contacts with the probes. If the thermostat is working properly and is in a warm state, the circuit should be closed (the device will beep or show zero/close to zero resistance).
- Place the thermostat sensing tube in a container of cold water (or apply ice) for a few minutes. When cooling, the contacts should blur, and the device will show infinity (break).
If the circuit does not ring at room temperature (break), it means that the contacts inside have oxidized or the mechanism is jammed. If, when the tube is cooled with ice, the contacts do not open, it means that the bellows has lost its elasticity or a gas leak has occurred. In both cases, it is necessary replacement of the thermostat to a new one.
Comparison table: Mechanical vs Electronic thermostat
Understanding the differences between types of regulators helps to quickly determine the diagnostic method. Mechanical devices are easier to test because their operation does not depend on the control board software. Electronic ones require a more complex approach.
| Parameter | Mechanical thermostat | Electronic sensor (thermistor) |
|---|---|---|
| Principle of operation | Gas expansion in bellows | Change in electrical resistance |
| Location | Inside the chamber, often in plain sight | Inside the housing, often hidden behind the casing |
| Checking | Contact testing + cold test | Resistance measurement with an ohmmeter |
| Typical breakdown | Freon leakage, contact sticking | Open circuit, change in rating |
Mechanical regulators, such as Tam 112 or K59, are easily replaced with analogues, even if the exact model is not found, the main thing is that the parameters of the capillary tube match. Electronic sensors are often unique to a specific series of refrigerators Samsung or LG, and their replacement requires precise selection according to the article.
The cost of mechanical thermostats is usually lower, and their installation takes less time. Electronic systems are more accurate, but their diagnosis often requires contacting a service center if you do not have access to technical documentation.
Replacing the thermostat: installation nuances
If the diagnostics confirmed the malfunction, the only option is replacement. When installing a new mechanical thermostat, it is critical to secure the capillary tube correctly. It should fit tightly to the surface of the evaporator in the same place where the old one was fixed. For fixation, special clamps or clamps are often used.
Be careful with the tube: it should not be bent, squeezed or scratched. Damage to the thin-walled tube will result in an immediate gas leak and the new thermostat will become inoperative. The length of the tube must match the original; if it is too long, the excess is carefully rolled into a ring, but is not cut off.
After installation, reassemble the refrigerator in reverse order. Plug in the device and set the control knob to the middle position. Start the refrigerator without loading food and monitor its operation for several hours. The compressor must periodically turn on and off, maintaining the set mode.
⚠️ Attention: The technical characteristics of thermostats (capillary length, temperature response range) may differ even for models from the same manufacturer. Use only compatible spare parts specified in the catalogs for your modification.
Frequently asked questions (FAQ)
Is it possible to temporarily close the thermostat contacts to make the refrigerator work?
Yes, this is possible for temporary storage products if the compressor is working properly. Shorting the wires directly will start the motor in continuous mode. However, you cannot leave the refrigerator in this mode for a long time: the evaporator will become covered with ice, and the food in the chamber will freeze. In addition, the compressor may overheat without cyclic rest.
Why does the new thermostat not turn off the refrigerator?
There may be several reasons. Firstly, the capillary tube may have been installed incorrectly and is not in contact with the evaporator. Secondly, the new regulator itself may be defective or not suitable for the temperature range. Thirdly, the problem may not be in the thermostat, but in a freon leak, which is why the temperature in the chamber simply does not drop to the shutdown threshold.
How to check a thermostat without a multimeter?
It is difficult to carry out an accurate check without instruments. You can try the “elimination method”: if when you turn the control knob you can’t hear any clicks at all (when the refrigerator is plugged in) and the light is on, this may indicate a break. You can also gently knock on the thermostat body - sometimes the stuck contacts come off and the engine starts, but this is a temporary solution.
How much does it cost to replace a thermostat in a service?
The cost consists of the price of the spare part and the work of the technician. A mechanical thermostat is relatively inexpensive, but a specialist visit and diagnostics can account for a significant portion of the cost. Replacing it yourself saves the budget, but requires skills in working with power tools.
Does (room temperature) affect the operation of the thermostat?
Yes, especially in the cold season. If the refrigerator is in an unheated room (for example, on a balcony) at a temperature below +10°C, the mechanical thermostat may not turn on the compressor, since it believes that it is already cold inside. For such conditions, there are special climate classes of equipment.