If your refrigerator has stopped freezing, and the compressor is either silent or humming a couple seconds and clicks, in 80% of cases the culprit is starting relay. This tiny element is a key link in the engine starting chain, and its failure is the most common cause of breakdown of household appliances. Understanding what types of these devices exist will help you choose the right replacement and avoid repeated visits to the technician.
Modern and older models use fundamentally different motor start control circuits. Not only the operating algorithm, but also the characteristic sounds that the unit makes when it breaks down depends on the type of installed relay. In this article we will analyze in detail the design of the main types of relays, their differences and diagnostic methods.
The principle of operation of the starting mechanism
To start the compressor electric motor, it is necessary to create a torque, which is provided by the starting winding. However, you cannot keep this winding turned on all the time - it will burn out from overheating. It is starting relay that performs the function of a timer and switch, supplying voltage to the starting coil only at the moment of startup and turning it off when the rotor reaches the required speed.
In parallel with the starting task, the device often performs a protective function. Built-in or separate thermal release monitors current strength. If the compressor is jammed or the voltage in the network fluctuates, the relay breaks the circuit, preventing the expensive motor from burning out. Without this mechanism, starting would be impossible, and the service life of the equipment would be reduced significantly.
It is important to understand that different manufacturers use different approaches to implementing this scheme. If in old models "Atlant" or "Indesit" you will find bulky parts with moving contacts, then in modern "LG" or "Samsung" compact solid-state elements rule the roost.
⚠️ Attention: When diagnosing, always unplug the refrigerator from the mains. Working with live electrical components is deadly and can lead to electric shock.
Electromagnetic (current) relays
This is a classic type of device that has been installed in Soviet and early foreign refrigerators for decades. The principle of their operation is based on the physical movement of the core inside the coil. When voltage is applied, a starting current passes through the coil, the magnetic field draws in the core, which mechanically closes the contacts of the starting winding.
As soon as the engine starts, the current drops to the nominal value, the magnetic field weakens, and the core, under the influence of gravity (or a spring), falls down, opening the circuit. Such relays are often called “pill” relays because of their shape, although rectangular models are also available. They are highly reliable, but have one significant drawback - mechanical wear.
Over time, the contacts burn out, and the spring or core loses its properties, which leads to sticking. In this case, the starting winding remains on constantly, which causes a strong hum and subsequent shutdown due to overload. The characteristic click at startup is the sound of the core falling.
- 🔌 RT-K —the most common relay for old-style single-compressor refrigerators, installed vertically.
- 🔌 RT —a series of relays where the number after the letters indicates a modification, often used in two-compressor models.
- 🔌 P-1 - an analogue for low-power refrigerators, often found in minibars.
The main feature of electromagnetic models is their dependence on position. They work correctly only in a strictly defined position, indicated by an arrow on the body. If you turn the refrigerator over or install the part incorrectly, the mechanism will not work.
Posistor (thermal) relays
In more modern technology released after the 90s, electromagnets have given way to posistors. These are semiconductor elements whose resistance increases sharply when heated. In a cold state, the posistor passes current to the starting winding, allowing the motor to start.
The passing current heats the crystal, its resistance increases hundreds of times, and the current through the starting winding practically stops. In fact, the circuit breaks without mechanical movement of the contacts. After cooling (the cycle takes several minutes), the resistance drops and the relay is ready to start again.
Such devices are compact, cheap to manufacture and have no moving parts that could jam. However, they have the property of “aging”: over time, the crystal changes its characteristics, and the relay stops opening the circuit on time or, conversely, does not start the motor at all.
How to visually distinguish a posistor?
A posistor relay usually has a round or oval shape, often black or dark brown, and looks like a monolithic plastic block without visible moving parts parts inside a transparent housing.
Often a posistor element is combined with a thermal protective relay in one housing. This creates a universal module that is easy to replace. It is enough to remove the back cover of the compressor, disconnect the wires and install a new part.
Thermal protective relays
Deserves special attention thermal relay, which is often paired with a starting one, but performs a diametrically opposite function. If the starting device starts the motor, then the thermal device stops it in emergency situations. Inside there is a bimetallic plate that bends when heated.
Heating occurs in two ways: from the passing current (if it exceeds the norm) and from the heat of the compressor itself, to which the part is tightly pressed. When the temperature rises critically, the plate opens the contacts, de-energizing the engine. After cooling, the contacts close again and the cycle repeats.
Modern systems often use combined devices PTC-Starters, where the posistor and thermal protection are combined into a single unit. This simplifies the design, but requires a complete replacement of the module in case of any malfunction, even if only one of the elements burns out.
| Relay type | Principle of operation | Characteristic sign of failure | Resource |
|---|---|---|---|
| Electromagnetic | Retraction of the core by current | Loud click, buzzing | High |
| Posistor | Heating crystal | Silence or quiet crackling | Average |
| Thermal | Bending of the bimetallic plate | Frequent shutdowns | High |
| Electronic | Chip control | No response | Very high |
Do not ignore frequent clicks of the thermal relay. This is a signal that the compressor is overloaded, possibly due to a dirty condenser or a lack of freon.
Electronic starting devices
In premium refrigerators with inverter compressors, traditional relays may be absent as a class. inverter control unittakes over their function. The electronics smoothly increases the frequency of the current, starting the motor without sudden surges of current and mechanical switching.
This system allows the compressor to operate continuously, adjusting power from 0 to 100%. The absence of mechanical contacts and sudden starts significantly extends the life of the unit and reduces the noise level. However, diagnosing such systems requires special equipment and knowledge.
If in a regular refrigerator replacing a relay costs a penny, then failure of the inverter module is an expensive repair. Often, technicians suggest replacing the entire compressor complete with electronics, since searching for individual components may not be economically feasible.
⚠️ Attention: Inverter systems are sensitive to voltage changes in the network. To protect them, it is strongly recommended to use a voltage stabilizer.
Diagnostics and signs of malfunction
You can understand that the relay has failed by its characteristic symptoms. The most obvious sign is that the compressor tries to start, a click is heard, but the motor does not start, and after a while the click repeats. This is a classic picture of “thermal stroke”, when a protective relay saves the motor from burning out.
Another option is that the refrigerator is silent, although the light bulb inside is on. This may mean that the start relay contacts have oxidized or burned out, and the current simply does not reach the windings. In rare cases, the relay may “stick” when turned on, which will lead to overheating and buzzing.
For an initial check, you can carefully remove the relay (after turning off the power!) and shake it near your ear. If a ringing or knocking sound is heard inside, as if from broken glass, it means that the ceramic element or core is damaged - the part requires replacement.
☑️ Primary diagnosis of the relay
It is also worth paying attention to the appearance of the plastic case. Blackening, melting or a burning smell indicate that a short circuit or overheating has occurred inside.
Replacement and selection of analogues
Replacing a relay is one of the few procedures available to a home craftsman. The main rule: you need to buy a part with exactly the same marking or its complete analogue. The coil parameters and posistor characteristics are selected for the specific motor power.
There are no universal solutions “for all refrigerators”, although some manufacturers produce adapters. For example, a relay RT can often be replaced with PTC with a corresponding adapter, but it is better to look for the original. The marking is usually applied to the side or top edge of the case.
The replacement process is simple: remove the old part, remember (or take a photo) the order of connecting the wires, and install the new one in the same position. It is important to ensure tight contact between the terminals. If the connectors are oxidized, they can be carefully cleaned.
After installation, turn on the refrigerator and listen. Startup should be quiet, without loud clicks or buzzing. If the motor started and after 10-15 minutes cold appeared in the chamber, the repair was completed successfully.
⚠️ Attention: Compressor characteristics and relay compatibility may vary depending on the production batch. Always check the markings on the part body with manufacturers’ catalogs or consultants.
Frequently asked questions (FAQ)
Is it possible to start a refrigerator without a relay?
Theoretically, you can start the motor by applying voltage directly to the starting winding, but doing this is strictly prohibited in living conditions. Without a protective relay, the compressor will burn out in a few minutes at the first overload or power surge.
How much does it cost to replace the relay?
The part itself is inexpensive, from 300 to 1500 rubles, depending on the model and manufacturer. The work of a replacement technician is usually estimated at 1000-2000 rubles, plus travel. Self-replacement saves the budget.
Why does the new relay burn out?
If the new relay burns out quickly, then the problem is not in it, but in the compressor. Turn-to-turn short circuit of the motor windings causes excessive current, which melts even a working relay. In this case, the compressor needs to be replaced.
How to determine which relay is needed: RTK or RT?
Look carefully at the markings of the old device. The installation position also matters: RTKs are usually installed vertically (the rod moves up and down), and RTKs can be horizontal. Incorrect orientation will not allow the mechanism to work.
Is it possible to clean the relay contacts instead of replacing them?
In electromagnetic relays, you can carefully clean the contacts with fine sandpaper if they are simply burnt. However, there is nothing to clean in posistor relays - there is a solid crystal. Considering the low cost of the part, replacement is more reliable than temporary repair.