Has the refrigerator stopped freezing or, conversely, turned food into ice blocks? Often the root of the problem is a small but critical element - the thermal relay. It is this component that is responsible for maintaining a given temperature regime, opening and closing the electrical circuit of the compressor at the right time. Understanding how this mechanism works will help you diagnose the malfunction yourself and avoid an expensive call to a technician.
Inside the body of the refrigerator compartment there is a complex thermoregulation system. Thermal relay (or thermostat) is its “brain center”, which reads the readings from the sensor and makes a decision whether to turn the motor on or off. If you notice that the unit is running without interruption or starts too rarely, this cannot be ignored. A malfunction of the sensor can lead to overheating of the compressor or damage to food supplies.
In this article we will analyze in detail the thermal relay device, the principle of its operation and step-by-step instructions for checking the serviceability of the part. You will learn what tools are needed for diagnosis and how to distinguish a relay failure from other cooling system faults. A competent approach to repair will extend the life of your household appliance.
The principle of operation and design of the thermostat
The basis of any mechanical thermostat is a bellows tube filled with refrigerant (freon or other gas with a low boiling point). This gas is in a closed volume and is sensitive to temperature changes. When the air in the chamber heats up, the gas expands, creating pressure on the walls of the bellows. This pressure is transmitted to the contact group, closing the circuit and starting the compressor.
As soon as the temperature inside reaches the set value, the gas is cooled and compressed. The pressure drops and the spring opens the contacts, stopping the motor. In electronic models Atmor or Indesit thermistors are used instead of gas, the resistance of which changes depending on the heating, but the logic of operation remains similar. The main difference is the absence of moving mechanical parts in electronic sensors.
The design of the device includes several key elements:
- 🔹 Sensing element —a capillary tube or thermistor that is in direct contact with the cooled medium.
- 🔹 Contact group —moving and fixed contacts that switch electric current.
- 🔹 Adjusting screw —allows the user to set the desired temperature inside the chamber.
- 🔹 Spring mechanism —ensures the contacts return to their original position when the pressure changes.
⚠️ Attention: There is gas under pressure inside the bellows tube. Under no circumstances should you try to solder or open the relay housing - this may lead to an explosion or leakage of a dangerous substance. Electronic thermal relays, often found in modern models, operate on a different principle. There is no gas here, and the signal is generated based on changes in the electrical resistance of the semiconductor element. Such systems are more accurate, but require complex diagnostics using special equipment. Mechanical analogues are easier to replace, but may lose calibration over time.
Electronic thermal relays, often found in modern models Samsung And LG, work on a different principle. There is no gas here, and the signal is generated based on changes in the electrical resistance of the semiconductor element. Such systems are more accurate, but require complex diagnostics using special equipment. Mechanical analogs are easier to replace, but may lose calibration over time.
Types of thermostats: mechanical and electronic
There are two main types of thermostats on the household appliances market, and understanding their differences is important when selecting spare parts. Mechanical relays are universal and often fit refrigerators of different brands if the dimensions and length of the capillary tube are the same. Electronic models, as a rule, are original components for specific series of equipment.
Mechanical devices are marked with a letter T (for example, T-110, T-133) and have a characteristic long copper tube. They are reliable, but are subject to wear of the contact group. Electronic analogues are compact, do not have long tubes and are connected via a connector. Their diagnosis often comes down to measuring resistance, while the mechanic needs to “listen” and check the patency of the contacts.
Comparative characteristics of relay types:
| Parameter | Mechanical relay | Electronic relay |
|---|---|---|
| Principle of operation | Gas expansion in the bellows | Change of resistance thermistor |
| Accuracy | Average (error 2-3°C) | High (error up to 0.5°C) |
| Service life | Limited contact wear | High, but afraid of power surges |
| Cost | Low | High |
When choosing a replacement, it is important to pay attention not only to the type, but also to the temperature range of operation. There are different models used for single-compartment refrigerators and freezers. For example, a relay marked T-110 is designed for lower temperatures than T-130. Installing an unsuitable element will lead to incorrect operation: either the chamber will constantly defrost, or the food will freeze.
Symptoms of a thermostat malfunction
Diagnostics begins long before disassembly housings. Careful observation of the operation of the refrigerator allows you to identify signs of thermal relay failure with high accuracy. If you notice that the motor hums continuously without turning off for hours, this is a sure sign that the circuit is not opening. The contacts are “stuck” in the closed state, and the compressor is working for wear.
The opposite situation - the refrigerator does not turn on at all, although the light in the chamber is on. This means that the circuit is open and does not close even when the temperature rises. The compressor is silent, and the food begins to deteriorate. In some cases, the relay may work, but with a long delay or erroneous readings, which leads to frequent switching on and off of the motor.
Main signs of failure:
- 🚫 The compressor works without stopping, the “fur coat” on the back wall freezes.
- 🚫 The refrigerator is silent, the temperature in the chamber is rising, although there is light.
- 🚫 Too frequent on/off cycles (cycles less than 5-7 minutes).
- 🚫 The chamber is too cold or too warm, regardless of the position of the regulator.
Sometimes the cause of unstable operation is not the relay itself, but the displacement of the sensitive tube. If the capillary has fallen out of the mounting hole or does not fit well to the evaporator wall, it will not read the temperature correctly. In such cases, replacement of the part is not required - it is enough to correctly install the tube in its original place.
Dismantling and visual inspection of the part
Before proceeding with electrical measurements, it is necessary to remove the thermal relay from the housing. For most mechanical models, access is through a plastic trim inside the refrigerator compartment where the temperature control is located. By carefully prying it up with a flat-head screwdriver, you will gain access to the mounting screws.
After removing the regulator, you will need to dismantle the internal panel, behind which the thermostat itself is hidden. Be careful with the capillary tube - it is very thin and easily breaks when bent. Capillary can be fixed to the evaporator wall with special clamps; they need to be carefully bent to release the tube.
☑️ Preparation for dismantling
During a visual inspection, pay attention to the condition of the contacts. If you see black carbon deposits, melted plastic or traces of sparking, the part definitely needs to be replaced. Also check the integrity of the insulation of the wires and the tube itself. Any mechanical damage to the relay body makes its further operation impossible and dangerous.
⚠️ Attention: Before starting any work, be sure to disconnect the refrigerator from the power supply! Working with live electrical appliances is deadly.
In electronic models, the process is simpler: the sensor is usually located inside the chamber or in the air duct and connected through a connector. It is enough to disconnect the chip and remove the sensor from its seat. However, in some modern systems, access to the sensor may be hidden behind decorative panels that require partial disassembly of the internal space.
Checking the thermal relay with a multimeter
The most reliable diagnostic method is to check the conductivity of the contacts using a multimeter. Switch the device to continuity or resistance measurement mode (Ohm). For a mechanical relay, the probes need to be connected to the contacts that go to the compressor. In normal condition at room temperature, the contacts should be closed (the device will beep or show zero).
To check the openness, place the relay sensitive tube in a container of ice water for 2-3 minutes. After cooling, the gas inside should compress and the contacts will open. If the multimeter continues to show a short circuit (“0”) even after freezing, it means that the mechanism is jammed or the bellows seal is broken.
Algorithm for checking the electronic sensor:
- Measure the resistance of the sensor at room temperature (usually 5-10 kOhm).
- Place the sensor in the cold (freezer) for 5 minutes.
- Measure the resistance again - it should change (rise or fall depending on the type of thermistor).
- If the resistance does not change or shows a break ("1" or infinity) - the sensor is faulty.
Nuances of checking two-pin and three-contact relays
In two-contact relays, the main circuit is checked. In three-pin ones (with a signal lamp), one contact goes to the lamp. When making calls, it is important not to confuse the contacts: the lamp contact may not ring with the main one. Look for a pair that closes/opens when the temperature changes.
If the multimeter shows no response to temperature changes, the part must be replaced. It is almost impossible to repair thermal relays due to their sealed design and the low cost of new analogues. Buying a new element will cost less than trying to restore the old one.
Replacing and setting up a new thermostat
Installing the new part is done in the reverse order. The main requirement is to carefully lay the capillary tube. It should fit snugly against the evaporator wall in the same places where the old one was attached. Use standard clamps or aluminum tape to secure, but do not pinch the tube. It is prohibited to bend it at an acute angle - this will lead to fracture and gas leakage.
After assembling the case and connecting the wires, it is necessary to carry out the initial setup. The adjustment screw is usually hidden under the plastic knob of the regulator. By turning the screw you can adjust the on and off temperature. Factory settings, as a rule, are already optimal, but when installing an analogue, adjustments may be required.
After replacement, turn on the refrigerator and leave it to work without loading food for 4-6 hours. This will allow the system to return to operating mode and stabilize the temperature. If during this time the on/off cycles occur normally (for example, it works for 10 minutes, rests for 20), then the replacement was successful.
How often do you need to change the thermal relay?
The thermal relay is a part with a limited resource, but it does not require scheduled replacement. The average service life of a mechanical relay is 7-10 years. Electronic sensors may last longer, but are more sensitive to power surges. Replace only when signs of malfunction appear.
Is it possible to temporarily short-circuit the relay?
Technically, you can connect the wires directly to start the compressor, but this is strictly not recommended for long-term operation. The refrigerator will freeze endlessly, which will lead to freezing of food and damage to the compressor. This measure is only for diagnostics or emergency evacuation of products.
Why does the relay click, but the cold does not come?
The click means that the thermostat is trying to turn on the motor, but the compressor does not start. Reasons: faulty start relay, jammed compressor or problems with the motor windings. In this case, the thermostat itself may be working properly.
Does the length of the capillary tube affect?
Yes, the length and diameter of the tube affect the reaction rate and gas volume in the system. When replacing, try to find an analogue with similar parameters. A tube that is too long can be carefully twisted into a ring, but it cannot be shortened or extended.
Where can I find the thermal relay markings?
The marking is applied to the metal body of the relay (for example, TAM-133, K59-L1102). To see it, you often have to remove the relay completely. Also, the spare part number can be found in the technical documentation for the refrigerator or on the websites of spare parts manufacturers according to the model of the unit.