Every owner of modern household appliances knows that a stable temperature inside the chambers is the key to food safety. However, few people think about exactly what mechanism makes the compressor turn on and off at the right moment, creating an ideal microclimate. This “brain center” of the cooling system is a thermostat, or thermostat, without which the operation of the unit would be impossible.
It is this small device that constantly monitors changes in temperature conditions and sends signals to start or stop the engine. If you notice that the food in the refrigerator begins to freeze or, conversely, deteriorate from the heat, and the compressor works continuously or is silent for hours, then most likely the problem lies in its settings or a complete breakdown.
Understanding how it works thermostatwill help you carry out initial diagnostics yourself and avoid calling a repairman for trifles. In this article, we will analyze in detail the principle of operation of the device, types of designs and algorithms for testing functionality.
The basic principle of operation of the thermostat
The functioning of the refrigerator is based on cyclic cooling of the internal volume, and the thermostat here acts as the main control element. Inside the device body there is a sensitive tube filled with freon or other gas, which reacts to the slightest changes in ambient temperature. When the air in the chamber heats up above the set norm, the gas expands, the pressure in the tube rises, and the contacts inside the relay close.
An electrical impulse is transmitted to the compressor, starting the cooling process. Once the temperature reaches a predetermined minimum, the gas is compressed, the contacts open and the engine stops. This process occurs constantly, providing a stable temperature background. It is important to note that operation range may vary depending on the model and user settings.
There are two main types of these devices: mechanical and electronic. Mechanical thermostats, such as TAM 133 or K-59work solely on the physical properties of gases and springs, without requiring complex electronics. Electronic analogues use thermistors and transmit digital signals to the main control board, which allows you to control the temperature with an accuracy of a degree.
It is worth remembering that correct operation mechanical thermostat directly depends on the tightness of the capillary tube to the evaporator. If the tube comes loose or moves, the readings will be incorrect, which will lead to malfunctions of the entire system.
Design features and types of devices
The variety of refrigerator models gives rise to many modifications of thermostats. Understanding their design is necessary when selecting spare parts for repair. The main element of any mechanical thermostat is a sealed bellows, which is compressed or expanded under the influence of gas pressure in the sensitive tube.
Inside the housing there is also a group of contacts and a spring mechanism that regulates the compression force. By turning the knob on the front panel of the refrigerator (or changing the position of the screw inside), the user changes the spring tension, setting the response threshold. Electronic temperature sensors are designed differently: they change their electrical resistance depending on heating.
- 🔹 Mechanical thermostats: are reliable, repairable, but have an error in readings and can click during operation.
- 🔹 Electronic thermostats: provide high accuracy, are silent, but require working electronics and are often beyond repair.
- 🔹 Thermal relay with air tube: the sensitive element is located in the air flow, and not on the evaporator wall, which is typical for the system No Frost.
When choosing a replacement, it is important to pay attention not only to the appearance, but also to the markings. For example, series thermostats K-50 are often used in single-chamber models, while TAM-133 are intended for two-chamber units. An incorrectly selected analogue can cause the refrigerator to freeze too little or, conversely, turn the chamber into a freezer.
⚠️ Attention: The capillary tube of a mechanical thermostat is very thin and easily damaged. During installation, it is forbidden to bend it at an acute angle or stretch it, since a violation of the tightness will lead to a gas leak and complete inoperability of the part.
Typical signs of a thermostat malfunction
Diagnostics of malfunctions often begins with monitoring the behavior of the refrigerator. If you notice that the unit is behaving uncharacteristically, the first thing to suspect is the thermostat. Symptoms can be varied, but they all boil down to a temperature imbalance.
The most obvious sign is that the compressor works without interruption, trying to catch up to a temperature that the sensor “does not see.” In this case, the food in the main chamber may become covered with ice, and a “fur coat” will form on the back wall. The opposite situation, when the engine is silent and the refrigerator is warm, also indicates that relay contacts do not close.
☑️ Symptoms of thermostat failure
Sometimes the malfunction manifests itself in the form of a short operating cycle: the unit turns on, runs for a couple of minutes and turns off. This may indicate sticking contacts or a malfunction of the spring mechanism. It is also worth paying attention to the adjustment knob: if it scrolls freely, without characteristic resistance, the internal mechanism may be broken.
| Symptom | Probable cause | Recommended action |
|---|---|---|
| The compressor does not turn on | Open circuit in the thermostat | Ring the contacts with a multimeter |
| Continuous operation of the motor | Contacts do not open | Replace the thermostat |
| Ice build-up in the chamber | Incorrect sensor readings | Check the position of the tube |
| Frequent switching on/off | Sticking contacts | Relay diagnostics |
You should not ignore even the slightest deviations in operation, since constant overload of the compressor due to a faulty thermostat can lead to its combustion, which is a much more expensive repair.
Diagnostics and testing with a multimeter
For accurate Determining a malfunction by visual inspection is not enough. The most reliable way to check mechanical thermostat is to test the contacts using a multimeter. This method allows you to determine with a high degree of probability whether the circuit closes when the temperature changes.
Before starting diagnostics, it is necessary to turn off the power to the refrigerator and remove the thermostat. Remove the regulator handle, unscrew the mounting screws and carefully remove the housing. Disconnect the wires from the terminals, having previously photographed their location so as not to confuse them during assembly.
The testing process is as follows: set the multimeter to the continuity mode, touch the two main contacts with the probes (usually they are marked with numbers 3 and 4 or 3 and 6). At room temperature, the circuit should be closed and the device will beep. Then place the sensitive tube in the cold (you can use the freezer for a couple of minutes) - depending on the type of thermostat, the circuit should break or remain closed.
If the multimeter shows an open circuit in both cases (in both heat and cold), then the contacts have oxidized or burned out, and the part requires replacement. It is also worth checking whether there is a breakdown in the body: press one probe to the metal part of the thermostat body, and the second to the contact - the device should be silent.
Instructions for replacing the thermostat with your own hands
Replacing the thermostat is a procedure that can be performed at home if you have basic skills and tools. The main thing in this process is accuracy, especially when working with a capillary tube. First, make sure that the refrigerator is unplugged for at least 2 hours.
Remove the top cover of the refrigerator (or the plastic cover that hides the thermostat). Disconnect the temperature control knob. Carefully remove the old thermostat, being careful not to damage the interior of the chamber. Disconnect the wires and remove the device.
Install the new device into the seat. Secure the sensing tube in the same position as the old one, using standard latches or clamps. Connect the wires according to the photograph or color marking you took earlier. Reinstall the regulator knob.
⚠️ Attention: It is strictly forbidden to turn on the refrigerator immediately after installing a new thermostat if you soldered or used sealants. Wait for the materials to dry completely and the components to cool.
After assembly, turn on the refrigerator. The initial cooling cycle may take longer than usual. Do not load the chambers with products during the first day of operation, let the unit return to operating mode.
Adjustment and calibration after installation
After replacing the thermostat, it is often required to be adjusted. Factory settings may not perfectly match your refrigerator's requirements or operating conditions. The adjustment is carried out using a special screw located inside the thermostat housing or under the seal.
Turning the screw clockwise usually increases the spring tension, which shifts the temperature threshold towards lower values (the refrigerator will turn off earlier). Counterclockwise - the temperature inside the chamber will be lower. Be careful: one full turn of the screw can change the temperature by 2-3 degrees.
For accurate calibration, use an external thermometer placed in a glass of water in the center of the chamber. Let the refrigerator run for a few hours, then take the readings. If the temperature does not correspond to the desired one, make (fine adjustments) with the screw.
It is important to consider that in refrigerators with a system No Frost tuning can be more complex, since the sensor responds to the temperature of the air, not the wall. Here, the correct positioning of the tube in the air channel is critical.
Frequently asked questions (FAQ)
Is it possible to temporarily close the thermostat contacts to make the refrigerator work?
Yes, this is possible for a short-term check of the compressor or in an emergency to preserve food until the technician arrives. However, you cannot leave the refrigerator in this mode for a long time: the compressor will work without stopping, which will lead to its overheating, freezing of the evaporator and spoilage of food.
Why does the new thermostat click more often than the old one?
Frequent clicks may indicate an incorrect differential setting or that the sensitive tube does not fit tightly enough to the evaporator. Also, the reason may be incorrect operation of the newest device (defect) or problems with the compressor start relay.
What is the difference between the K-59 and TAM-133 thermostat?
The main difference is the response temperature range and the length of the capillary tube. K-59 usually used in two-chamber refrigerators and has a lower shutdown temperature, while TAM-133 is often used in models with one compressor for two chambers. Installing an unsuitable model will lead to a violation of the temperature regime.
How long does the refrigerator work after replacing the thermostat before the first shutdown?
The time of the first cycle depends on the volume of the chambers, the number of products and the ambient temperature. Normally, the refrigerator should reach temperature and turn off after 1.5–3 hours of continuous operation. If it works for more than 5-6 hours without a break, it is necessary to check the tightness of the system and the correct installation of the thermostat.