A sudden stop of operation of the refrigerator or a characteristic click, after which the motor is silent, often baffles the owner. In most cases, the cause is not a breakdown of the compressor itself, but a failure of the protective automation, in particular start-protective relay. This small element plays a critical role in the electrical circuit of the unit, ensuring safe starting of the engine and protecting it from overloads. Understanding exactly how this unit works will help you diagnose the problem yourself and avoid an expensive call to a technician.
Thermal relay is not just a switch, but a complex electromechanical device that responds to changes in temperature and current. If the light in your refrigerator stops freezing, but the light is on, or the motor hums for a couple of seconds and suddenly stops, this component is often the culprit. In this article we will analyze in detail the structure of the mechanism, its interaction with compressor and the algorithm of actions when a malfunction is detected.
Ignoring the symptoms of a relay malfunction can lead to burnout of the motor windings, which will turn a simple repair into a replacement of an expensive unit. Therefore, it is important to pay close attention to the sounds your refrigerator makes and promptly check the condition of the electrical circuit.
Operation principle and design of the protective mechanism
To understand why a thermal relay is needed, you should consider its design. The device is a housing, inside of which there is a heating coil, a bimetallic plate and a contact group. Bimetallic plate is a key element: it is made of two metals with different coefficients of thermal expansion, soldered together. When an electric current passes through the spiral, the plate heats up and bends, opening the contacts and de-energizing the compressor.
In normal operation, the relay is in a closed state, passing current to the motor windings. However, if a voltage surge occurs or the piston group jams, the current in the circuit increases sharply. The coil heats up more than usual, causing the plate to bend and break the circuit. This process prevents the insulation from overheating and the windings from melting. After cooling, the plate returns to its original position, closing the contacts again, which allows you to try to start the motor.
It is important to note that modern relays are often combined with a starting device. Until the motor rotor reaches the required speed, the starting winding operates in enhanced mode. As soon as the engine reaches operating mode, the current drops and the relay turns off the starting winding, leaving only the working winding. Violation of this balance is a sure sign that start-protective relay requires replacement.
⚠️ Attention: If, after clicking the relay, you hear repeated startup attempts at intervals of several minutes, do not try to constantly plug in the refrigerator. This can lead to the final failure of the compressor.
Why does the relay click but does not start the motor?
Clicks indicate that the protection mechanism is triggered. This happens when the current in the circuit exceeds permissible limits. The relay “sees” the overload and opens the contacts. If, after cooling, it closes the circuit again, and the engine cannot turn over (due to jamming or a malfunction of the relay itself), the cycle repeats. Frequent clicks are a signal that the protection system is working, but the problem in the engine or starting mechanism has not been solved.
The main functions of a thermal relay in a cooling system
The main task of this component is to ensure safety. There are several key functions that the device performs in conjunction with the motor:
- 🛡️ Overload protection: prevention of a critical increase in current in the motor windings, which could cause a fire or short circuit.
- 🌡️ Thermal regulation: temperature control of the compressor housing. If the motor overheats due to poor ventilation or prolonged operation, the relay opens the circuit.
- 🔄 Start control: in combined devices, the relay provides a short-term voltage supply to the starting winding to create torque.
- ⚡ Voltage stabilization: smoothing out minor fluctuations in the network, although serious protection against surges still requires a separate stabilizer.
Without a working relay, the refrigerator will not be able to function normally. Even if you manage to run the compressor bypassing the protection, the risk of it burning out within a few hours of operation is almost 100%. Therefore thermal protection is an integral part of the design of any household refrigeration equipment.
It is also worth mentioning that in different models of refrigerators, such as Indesit, Atlant or Beko, relays with different characteristics can be used triggering. The selection of an analogue should be made strictly according to the markings indicated on the body of the old device.
Typical signs of a faulty start-up protective relay
Diagnostics of the fault often does not require sophisticated equipment. An attentive user can notice the symptoms of a breakdown by external signs. Most often, a malfunction is indicated by the situation when compressor tries to start, emits a beep, but after a few seconds a click is heard and silence ensues. This is a classic symptom of thermal protection tripping or failure of the starting mechanism.
Another sign may be a complete failure of the equipment to turn on when there is voltage in the outlet. If the light inside is on, but the motor is silent, the contacts inside the relay may have oxidized or the heating coil has burned out. In some cases, the relay may “stick” in the closed state, due to which the compressor operates continuously without turning off, which leads to intense ice formation in the chamber.
Visual inspection can also give results. If you remove the back cover and dismantle the relay, you will notice:
- 🔥 Case melting: indicates overheating and breakdown of insulation inside the device.
- 🌫️ Smoking smell: a clear sign that irreversible changes have occurred inside.
- 🔊 Knock when shaking: if something is loose inside the relay, it means that the bimetallic plate or contacts have come off the fastenings.
⚠️ Attention: Before any visual inspection or dismantling of parts, be sure to disconnect the refrigerator from the power supply! Working with live electrical components is deadly.
Instructions for replacing the relay yourself
Replacing a thermal relay is one of the most accessible procedures for a home craftsman. It does not require soldering or special skills if you act carefully. The first step should always be to complete dismantling the device from its standard location. Usually the relay is placed on three contact pins of the compressor and secured with a bracket or plastic box.
The replacement process is as follows:
- Unplug the refrigerator and move it away from the wall to access the back panel.
- Remove the protective plastic cover covering the compressor.
- Carefully remove the old relay from the compressor contacts. Pay attention to the orientation: the top is usually marked with an inscription
TOPor an arrow. - Compare the markings of the new and old relay. They must match the electrical characteristics.
- Install the new device on the contacts until a characteristic click is heard and secure it.
- Close the protective casing and turn on the refrigerator.
☑️ Checklist before replacing the relay
After turning on, listen to the operation of the motor. If it starts up smoothly, without buzzing and subsequent clicks, and after a while cold appears in the chambers, it means the replacement was successful. If the symptoms persist, the problem may lie deeper - in the compressor itself or the wiring.
Compatibility and relay characteristics table
When selecting a spare part, it is important to consider not only the brand of the refrigerator, but also the engine power. Below is a table with examples of correspondence between relay types and equipment models.
| Relay type | Motor power (W) | Compatible brands | Features |
|---|---|---|---|
| RT-21 | up to 200 | Atlant, Minsk | Vertical installation |
| R-3 | up to 150 | Biryusa, Oka | Horizontal installation |
| K-144 | up to 250 | Indesit, Ariston | Combined |
| PTC-Start | up to 300 | Samsung, LG | Posistor type |
Always check the technical documentation or markings on the compressor nameplate.
Prevention and extension of service life
In order for the thermal relay and the compressor to serve as long as possible, you must follow simple operating rules. First of all, this is to ensure good ventilation in the compressor area. Dust, animal hair and dirt that accumulate on the condenser (the black grille at the back) impair heat transfer. The motor is forced to work longer and more intensely, which increases the temperature and load on the relay.
Regular cleaning behind the refrigerator is the best prevention. Once every six months, it is recommended to move the unit and vacuum the back wall. You should also avoid installing the refrigerator close to a wall or in niches without an air gap. Overheating is the main enemy of electrical components.
In addition, it is worth paying attention to the stability of the voltage in the network. Although the relay protects against current surges, constant voltage surges can accelerate wear on the bimetallic strip. Using a surge protector or voltage stabilizer will be an additional investment in the durability of your equipment.
⚠️ Attention: The design and location of elements may vary depending on the model and year of manufacture. If you are not confident in your abilities, it is better to contact an authorized service center so as not to violate the warranty or damage other components.
Can an old relay be repaired?
There are no parts inside the relay that can be repaired at home. Disassembling the housing usually leads to its destruction, and calibration of the bimetallic strip requires factory equipment. Attempts to clean the contacts or bend the plate give a short-term effect and are unsafe. The only correct solution is to replace it with a new, working unit.
Frequently asked questions (FAQ)
Why does a new relay immediately burn out after installation?
This may indicate a serious problem with the compressor itself, for example, an interturn short circuit of the windings. The motor draws a current well in excess of the rated current, and the new protection immediately trips or burns out. Also, the reason may be a faulty wiring or thermostat that prevents the motor from turning off.
Is it possible to start a refrigerator without a thermal relay?
Theoretically, you can start the motor by connecting the wires directly, but this is strictly prohibited. Without protection, any voltage surge or piston jamming will lead to combustion of the compressor, which costs much more than a relay. In addition, this creates a risk of fire in the apartment.
How to distinguish a starting relay from a thermal one?
In many modern models this is a single unit - a starting and protective relay. However, in older refrigerators they could be separate. A thermal relay usually has the form of a “tablet” with contacts and a heating element, and a starting relay often contains a posistor or electromagnetic mechanism. There are always markings and a connection diagram on the case.
How much does it cost to replace a relay in a service?
The cost consists of the price of the spare part itself (which is usually low) and the work of a technician to visit and diagnose. Self-replacement allows you to save on the cost of work, which can be a significant part of the check amount.