Thermal relay (or thermostat) is a small but critical element of the refrigerator, on which temperature stability, efficiency and even the service life of the equipment depend. Without it, the compressor would either run continuously, overheating and consume huge amounts of electricity, or not turn on at all, allowing food to spoil. However, many users are not even aware of its existence - until the refrigerator begins to “act up”.
In this article we will analyze how a thermal relay workson what principle it regulates the temperature, what signs indicate its malfunction and whether it is possible to repair or replace the part yourself. You will also learn how modern electronic thermostats differ from mechanical ones, and why in some models (for example, No Frost) their role is played by sensors and control boards.
The material will be useful for both owners of old Soviet refrigerators (ZIL, Minsk, Biryusa) and modern devices (Samsung, LG, Indesit, Atlant). We avoid complex technical terms, but if necessary, we provide explanations in spoilers.
What is a thermal relay and where is it located in the refrigerator
Thermal relay (thermostat, temperature relay) - this a device that automatically turns the compressor on and off depending on the temperature inside the chamber. Its main task is to maintain a given mode (usually from +2°C to +8°C in the refrigerator compartment and about -18°C in the freezer) without user intervention.
Externally The thermal relay looks like a small box with contacts and a bellows tube (thin copper or capillary tube), which is attached to the evaporator. In older models, the thermostat is mechanical and located inside the refrigerator compartment (often hidden under a plastic case next to the temperature control knob). In new refrigerators it can be:
- 🔧 Built into the control panel (electronic models with a display).
- 🧊 Located next to evaporator (in devices with a system No Frost).
- ⚙️ Hidden behind the rear panel (in combined models with two compressors).
In refrigerators with No Frost instead of the classic thermostat, thermistors (temperature sensors) and electronic boards are often used, which analyze the readings and control the operation of the fans and compressor. However, the principle remains the same: maintaining the set temperature.
The principle of operation of the thermal relay: how it regulates the temperature
The operation of the thermal relay is based on physical properties of gases and liquidslocated inside the bellows tube (capillary). a refrigerant (usually freon or its analogue) that reacts to changes in temperature. When the air in the refrigerator heats up, the gas expands, creating pressure on the membrane inside the relay. The membrane, in turn, closes the contacts that turn on the compressor.
The operating cycle of the thermostat looks like this:
- The temperature rises → the gas in the capillary expands → the pressure on the membrane increases → the contacts close → the compressor turns on.
- The temperature drops to the set value → the gas is compressed → the pressure drops → the contacts open → the compressor turns off.
In mechanical thermostats, the response threshold is set control knob (usually in divisions from 1 to 7). chamber and the compressor will turn off less often. In electronic models, the temperature is set using buttons on the panel or via the touch display.
What is hysteresis in a thermostat?
Hysteresis is the difference between the temperature when the compressor turns on and off. For example, if the thermostat is set to +4°C, the compressor can turn on at +6°C and turn off at +2°C. This prevents too frequent engine starts, which lead to its wear.
In refrigerators with No Frost the process is more complicated: in addition to the thermostat, defrost timer, evaporator sensor and fan. The system analyzes not only the air temperature, but also the condition of the evaporator (ice) to prevent freezing.
Symptoms of malfunction thermostat: when it's time to sound the alarm
If the thermostat fails, the refrigerator stops maintaining the correct temperature. Here are main symptomsindicating the problem:
- ❄️ The compressor works continuously (does not turn off even at low temperatures).
- 🔥 The compressor does not turn on at all (it’s warm in the chamber, the food is spoiling).
- ⚡ Refrigerator freezes too much (the food freezes, ice builds up on the back wall).
- 🔄 The on/off cycles have become chaotic (the compressor clicks, but does not start or runs for 5-10 seconds and turns off).
- 💡 The light inside is on, but the refrigerator does not cool (there is power, but the signal is not sent to the compressor).
It is important to distinguish a thermal relay failure from other faults. For example, continuous operation of the compressor may be caused by:
- 🔌 Leakage of freon (refill required).
- 🧊 Clogged capillary tube (heat exchange is disrupted).
- 🔧 Breakdown of the compressor start relay.
To accurately diagnose the problem, you need check the thermal relay. You can do this yourself - we'll talk about this in the next section.
How to check the thermal relay. in the refrigerator: step-by-step instructions
Before checking unplug the refrigerator and take out all the products. You will need:
- 🔧 Screwdriver (Phillips or flathead).
- 📊 Multimeter (tester) for testing contacts.
- 🧊 Hair dryer or container with hot water (to simulate heating).
Step 1. Find the thermal relay
In older models (Atlant, Stinol, Nord) the thermostat is usually located inside the refrigerator compartment, under a plastic cover next to the adjustment knob. In modern refrigerators (Samsung RL-33, LG GA-B409) it can be hidden behind the back panel or in the control unit.
Step 2. Remove the protective casing
Carefully unscrew the screws and remove the plastic panel. The thermal relay is attached to 2-4 screws or latches. Pay attention to capillary tube —it cannot be bent or bent. damage!
Step 3. Check the contacts with a multimeter
Transfer the tester to the continuity mode (or resistance measurement). At room temperature, the thermal relay contacts should be closed (resistance ~0 Ohm). they are open - the relay is faulty.
To simulate heating, place the thermostat in a container of hot water (no higher +50°C) or direct a stream of air from a hair dryer onto it. A working relay should click open the contacts.
Disconnect the refrigerator from the mains|Remove the thermostat protective panel|Check the contacts with a multimeter in dial mode|Simulate heating (hot water or hair dryer)|Listen for a click operation-->
Step 4. Check the bellows tube
If the contacts do not operate, inspect the capillary tube for kinks, cracks or corrosion. A damaged tube does not transmit pressure to the membrane, and the relay does not work. In this case, the thermostat must be replaced.
Table: comparison of mechanical and electronic thermostats
Modern refrigerators are equipped with two types of thermostats: mechanical and electronic. Here are their key differences:
| Parameter | Mechanical thermal relay | Electronic thermal relay |
|---|---|---|
| Operating principle | Gas pressure in the capillary | Temperature sensors + microprocessor |
| Adjustment accuracy | ±2–3°C (step adjustment) | ±0.5–1°C (smooth adjustment) |
| Reliability | High, but sensitive to mechanical damage | Depends on the quality of the sensors and board |
| Maintainability | Cannot be repaired, only replacement | You can replace the sensor or board |
| Replacement cost | 1,000–2,500 RUR (depending on the model) | 2,000–5,000 RUR (sensor + board diagnostics) |
| Examples of refrigerator models | Atlant MXM 1705, Biryusa 18, Indesit B 18 | Samsung RB-30 J3200, LG GA-B489, Bosch KAN92VI30 |
Electronic thermostats are more accurate and allow you to implement additional functions (for example, Vacation mode or Super freezing), but their repair is more expensive. Mechanical relays are simpler and cheaper, but require manual adjustment.
Is it possible to repair a thermal relay yourself?
Mechanical thermal relays cannot be repaired - they can only be replaced. This is due to the fact that their body is sealed and the internal parts (membrane, contacts, capillary) are not intended for disassembly. However, there are several nuances:
1. Replacing the thermostat
If you are sure that the problem is in the thermostat, you can buy a similar one and install it yourself. The main thing is to choose a model with with the same temperature range are suitable and a connector. For example, for refrigerators Atlant thermostats K-59, TAM-133 or Danfoss 077B6.
2. Cleaning contacts
Sometimes the thermal relay does not work due to oxidation of contacts. They can be carefully cleaned with sandpaper or alcohol, but this is a temporary solution—soon the part will still have to be changed.
3. Checking the capillary tube
If the tube is bent or cracked, you can try straighten (without sudden movements!), but it is impossible to restore the tightness at home.
⚠️ Attention! In refrigerators with No Frost the thermal relay is often integrated into the control board. Independent replacement without experience can lead to damage to the electronics. In this case, it is better to contact a specialist.
How much does it cost to replace a thermal relay and where to order it
The cost of replacing a thermal relay depends on:
- 🏷️ Refrigerator models (parts are cheaper in older devices).
- 🔧 Thermostat type (mechanical or electronic).
- 📍 Region (in Moscow and St. Petersburg prices are higher than in small cities).
- 🛠️ Complexities of work (for example, in No Frost you will have to disassemble the control panel).
Approximate prices (for 2026):
- 🔹 Diagnostics — 500–1 000 ₽.
- 🔹 Replacement of a mechanical thermal relay — 1,500–3,000 ₽ (with part).
- 🔹 Replacement of an electronic thermostat/sensor — 2 500–5 000 ₽.
- 🔹 Repair of the control board (if the problem is her) - 3,000–8,000 ₽.
Where to order a replacement:
- Manufacturer's service centers (warranty repair).
- Private craftsmen (search on YouDo, Profi.ru).
- Repair shops (check the reviews!).
⚠️ Attention! If the refrigerator is on warranty do not open it yourself - this will lead to loss of warranty obligations. Contact an authorized service center.
FAQ: answers to frequently asked questions about the thermostat
Is it possible to do without a thermal relay and connect the compressor directly?
Technically yes, but this extremely dangerous. The compressor will work without stopping, which will lead to:
- 🔥 Overheating and motor breakdown.
- ⚡ Increased electricity consumption (up to 500–700 kW/month!).
- ❄️ Freezing of the evaporator and spoilage of food.
Without a thermostat, the refrigerator will last from several days to weeks.
What is the service life of a thermal relay?
On average, a mechanical thermal relay lasts 5–10 years., an electronic one - up to 15 yearsThe service life depends on:
- 🔄 Frequency of compressor switching on/off.
- 🌡️ Temperature changes (for example, if the refrigerator is next to the stove).
- ⚡ Quality of the electrical network (voltage surges shorten the life of contacts).
Why does the thermal relay click, but the compressor does not turn on?
This may indicate:
- 🔌 Failure of the start relay compressor.
- 🧊 Compressor jammed (needs replacement).
- 🔌 Motor winding break (checked with a multimeter).
- 🔌 Power problems (check the socket and power cord).
First make sure that the compressor is receiving voltage (220V).
Is it possible to repair the thermal relay with your own hands?
Mechanical thermal relay not being repairedbut you can:
- 🔧 Clean the oxidized contacts.
- 🔄 Check and straighten the capillary tube (if it is bent).
- 🔌 Check the reliability of the fastening and contacts.
If these measures do not helped - only replacement.
How to check the thermostat without removing it from the refrigerator?
You can perform quick diagnostics:
- Unplug the refrigerator.
- Remove the handle temperature adjustment and find two wires going to the thermostat.
- Close them together (for example, with a paper clip).
- Plug in the refrigerator.
If the compressor works, the problem is in the thermostat. If not, look for a fault in the compressor or the starter. relay.
⚠️ Attention! This method is temporary - do not leave the wires closed for a long time!