The basis of a stable operation of any refrigeration equipment is a temperature control system, the central element of which is a thermostat. It is this small but critical component that ensures the maintenance of the specified temperature inside the chambers, preventing food spoilage and the formation of excessive ice. Without a working sensor, the refrigerator turns into an ordinary cabinet, unable to perform its direct functions of preserving freshness.
Many users are faced with a situation where the unit begins to work incorrectly, but do not associate this with failure specifically thermostat. Understanding the principle of operation of this part will help you quickly diagnose the problem and avoid costly repairs of the compressor, which often suffers due to improper operation of the automation.
In this article we will analyze in detail the device of the thermostat, its role in the cooling cycle and learn how to identify the first signs of a malfunction. You will learn how to distinguish a sensor failure from problems with the refrigerant or engine, and also receive practical tips for checking the element yourself.
The operating principle and main functions of a thermostat
A thermostat, or thermostat, is an electromechanical or electronic device that continuously monitors the temperature inside the refrigerator compartment. Its main task is to open and close the electrical circuit that supplies power to the compressor, depending on the sensor readings. When the temperature rises above the set threshold, the contacts close, starting the motor. When the lower limit is reached, the circuit opens and the unit goes into standby mode.
It is important to understand that thermostat does not measure temperature directly, like a digital thermometer. Mechanical models use a bellows tube filled with freon or another gas-sensitive substance. This tube is attached to the evaporator or led into the chamber. When the temperature changes, the gas inside the tube expands or contracts, creating pressure on the membrane, which sets the switch contacts in motion.
Electronic models, often found in modern systems No Frost, work on a different principle. They use thermistors whose resistance changes depending on the heat. Such sensors transmit data to the main control module, which already makes the decision to start the compressor. The accuracy of electronic systems is higher, but the cost of replacing them is usually higher.
⚠️ Attention: Mechanical thermostats are sensitive to vibrations. If the refrigerator was shaken strongly during transportation, the calibration of the bellows tube could be lost, which will lead to incorrect shutdown of the engine.
The key function of the device is not only cooling, but also protecting the compressor from overloads. Without this element, the motor would work continuously, trying to achieve an unattainable ideal cold, which would lead to its rapid wear and increased energy consumption. Temperature adjustment Through the knob on the control panel, it actually changes the tension of the spring inside the thermostat, shifting the response thresholds.
Types of thermostats: mechanical and electronic systems
In the modern household appliances market, you can find two main types of regulators, each of which has its own design features and advantages. The choice of type depends on the class of the refrigerator, the year of its manufacture and the defrosting system used.
Mechanical thermostats, such as the popular models TAM or K-59, are simple and reliable. They are a sealed block with a bellows tube and a group of contacts. They are easy to diagnose with a multimeter “by ringing”, and they rarely fail suddenly, more often they simply “float away” from the calibration. Such devices are universal and are often suitable for replacement in models of different brands.
Electronic temperature sensors are integrated into the overall refrigerator control system. They have no moving parts, which makes them more durable in conditions of constant vibration. However, their diagnosis requires special equipment or a resistance tester. In systems with two compressors or zones Super Frost several sensors can be used to monitor different zones.
Below is a comparison table to help you understand the differences between the types of devices:
| Characteristics | Mechanical thermostat | Electronic sensor |
|---|---|---|
| Principle of operation | Gas expansion in the bellows | Change in thermistor resistance |
| Accuracy | Average (error 2-3°C) | High (error up to 0.5°C) |
| Diagnostics | Ringing contacts with a multimeter | Measuring resistance at different temperatures |
| Cost replacement | Low | High |
Symptoms of malfunction: when to sound the alarm
You can determine what refrigerator thermostat has failed by a number of characteristic signs that manifest themselves in changes operating mode of the unit. Ignoring these signals can lead to spoilage of a large number of products or breakdown of more expensive components.
The most obvious sign is the continuous operation of the compressor without entering the rest cycle. If the motor hums constantly and the temperature in the chamber drops below normal (the food in the refrigerator compartment freezes), this is a sure sign that the thermostat contacts are “stuck” in the closed state. The sensor simply does not “see” that the cold has already been reached and does not give a command to stop.
The opposite situation is also possible: the refrigerator does not turn on at all or operates in very short cycles, without having time to gain cold. In this case, it becomes warm inside the chambers, and the food begins to spoil. This indicates that the thermostat contacts are open and do not close even when the temperature rises, or the sensitivity of the element is completely lost.
- ❄️ Icing on the rear walls: If a thick “coat” of ice forms on the back wall of the refrigerator compartment even during normal operation, the thermostat may not turn off the compressor correctly, allowing the temperature to drop too low.
- 🔊 Clicks and lack of starting: A characteristic click when trying to turn on, after which the motor is silent, may indicate that the thermostat does not supply voltage to the starting relay.
- 💡 There is light, but no cold: The light in the chamber is on, which means there is power, but the compressor is silent. Often the culprit is a broken circuit in the thermostat.
Sometimes the symptoms can be vague. For example, a refrigerator works fine, but sometimes there are long downtimes or, conversely, overwork. This may indicate a “floating” fault, when contact is broken only at certain vibrations or temperatures.
⚠️ Attention: Before you mess with the thermostat, make sure that the refrigerator door is tightly closed and the seal is not damaged. Warm air from outside can force the compressor to work continuously, simulating a sensor breakdown.
Do-it-yourself thermostat diagnostics
Checking the thermostat is a procedure accessible even to a beginner, but requires compliance with safety precautions. The first step should always be to completely unplug the refrigerator. Working with live electrical wiring is prohibited.
For mechanical thermostats, the most reliable way is to check the contacts with a multimeter in continuity mode. It is necessary to remove the casing, find the thermostat and short-circuit the wires going to it (usually there are two or three, depending on the model and the presence of the lamp). If the refrigerator starts when the wires are shorted, then the problem is most likely in the thermostat itself.
A more accurate method is the “cold test”. To do this, remove the thermostat from the refrigerator (after defrosting the chamber) and place it in a container with cold water (about 0°C) for 5-10 minutes. After this, check the contacts: they should close with a click. If you remove the sensor from the water and heat it in your hands, the contacts should open. The absence of clicks or changes in the multimeter readings indicates a malfunction.
☑️ Thermostat diagnostics
When diagnosing electronic sensors, the multimeter is switched to resistance measurement mode (Ohms). Resistance values vary by model and temperature. Typically, at room temperature the resistance is a few kOhms, and when cooled it changes. It is better to look for exact data for your model in technical manuals. Samsung, LG or Indesit It's better to look in the technical manuals.
If you are not confident in your abilities or do not have the necessary tools, it is better not to take risks. Incorrect assembly or an error in connecting the wires can lead to a short circuit or failure of the compressor.
Replacing the thermostat: step-by-step instructions
If diagnostics confirm a malfunction, the thermostat must be replaced. It is important to choose an analogue that fully matches the original in terms of the length of the capillary tube, type of contacts and method of fastening. Using an unsuitable model may lead to incorrect operation of the entire system.
The replacement process begins with dismantling the old device. Carefully disconnect the wires, remembering their color coding or photographing the connection diagram. Remove the adjustment knob and unscrew the mounting screws. If the thermostat is mechanical, carefully remove the bellows tube from its seat in the evaporator, being careful not to damage it or bend it.
Installation of the new element is carried out in the reverse order. Pay special attention to fixing the sensitive tube: it should fit tightly to the evaporator in the same place where the original one was fixed. A special clamp or adhesive tape is often used for fixation. After installing all the components, assemble the case and turn on the refrigerator.
What to do if the capillary tube is longer than the original?
If the new tube is longer, it can be carefully rolled into a ring and secured inside the case without kinking or damaging it. The main thing is not to cut the tube, as this will break the tightness of the system.
After replacement, it is recommended to carry out a control temperature measurement using an external thermometer to ensure the correct operation of the new regulator. Adjustment may require several on-off cycles.
The influence of the thermostat on energy consumption and service life
Serviceable thermostat is a guarantee of energy savings. When the device is working correctly, the compressor turns on only when it is really necessary and works exactly as long as necessary to achieve the set temperature. A faulty sensor can cause the motor to wear out, which is reflected in electricity bills.
Continuous operation of the compressor without rest cycles leads to overheating of the motor windings and destruction of the oil in the lubrication system. This reduces the resource of the unit significantly. At the same time, if the thermostat “undercools” the food, bacteria begin to multiply faster, which jeopardizes the health of household members.
Modern models of electronically controlled refrigerators can diagnose sensor malfunctions independently. In this case, an error code may appear on the display indicating a problem with the temperature sensor. The decoding of the codes can be found in the instructions for the specific model.
⚠️ Attention: Characteristics of refrigeration equipment and error codes may vary between different manufacturers. Always check the technical documentation of your device before replacing parts.
Regularly checking the operation of the thermostat will help extend the life of your refrigerator. It is enough to pay attention to the duration of the operating cycles and the temperature inside the chambers once every six months in order to notice deviations in time.
Is it possible to operate a refrigerator with a faulty thermostat?
For a short time - yes, if you can control the temperature manually by turning the device on and off from the outlet. However, long-term operation is dangerous: either the products will deteriorate from the heat, or the compressor will burn out from overload. In addition, an ice block may form in the freezer, which is difficult to defrost.
Why does the thermostat click, but the refrigerator does not turn on?
The click means that the contacts inside the thermostat are closing and it is trying to start the compressor. If it does not start, the problem may be with the start relay, the compressor itself, or the wiring. It is also possible that the thermostat clicks, but the contact inside it is “burnt” and does not conduct current.
How often should the thermostat be changed?
The thermostat does not have a strict expiration date. High-quality mechanical models last 10-15 years or more. Electronic sensors are also durable. Replacement is required only when signs of a malfunction appear: incorrect temperature or continuous operation of the motor.
Does the temperature in the room affect the operation of the thermostat?
Yes, it does. Mechanical thermostats may not work correctly if the refrigerator is in an unheated room at a temperature below +10°C...+15°C. Under such conditions, the gas in the bellows may not expand enough to close the contacts, and the refrigerator simply will not turn on. For such conditions, special climate classes of equipment are needed.