A modern refrigerator is a complex electromechanical unit in which each element performs a critical function. Relay in this system they play the role of key switches that provide engine starting, overload protection and maintaining a given temperature. Understanding which relays are installed in your model will help you quickly diagnose a problem when the appliance stops freezing or starts making strange clicks.
Unlike simple household appliances, refrigeration equipment requires precise coordination of the operation of the compressor, fans and defrost system. It is relay elements that they take control of these processes. If you are faced with a situation where the motor hums but does not start, or, conversely, the refrigerator runs without stopping, most likely the problem lies in one of these components. Let's look in detail at what types of devices exist and how they affect the operation of the equipment.
It is important to note that the design may differ depending on the manufacturer and year of manufacture of the model. Old Soviet units used simpler mechanical circuits, while modern ones may not have classic starting relays in the traditional sense at all, using electronic control boards. However, for the vast majority of equipment in operation, knowledge of the structure of the relay group remains relevant. inverter refrigerators may not have classic starting relays in the traditional sense at all, using electronic control boards. However, for the vast majority of equipment in operation, knowledge of the relay group structure remains relevant.
Starting relay: principle of operation and device
The main element that ensures the start of operation of the refrigeration unit is starting relay. It is necessary in order to supply an additional impulse to the starting winding of the compressor motor at the moment of switching on. Without this initial jerk, the motor rotor simply would not be able to move due to the high freon pressure in the system and the inertia of the mechanical parts.
The operating principle of this device is based on electromagnetic induction. At the moment the voltage is applied, the current passing through the relay coil creates a magnetic field, which draws in the core and closes the contacts of the starting winding. As soon as the engine picks up speed and the current in the circuit drops to the nominal value, the core, under the influence of gravity or a spring, returns to its original position, opening the circuit. This process takes a split second, but it is critical for starting.
There are two main types of such devices: electromagnetic and posistor (thermal). Electromagnetic models are more often found in older refrigerators and are sensitive to installation orientation. Posistor analogues that can be found in modern models Indesit or Atlant, work by heating a special element, which changes its resistance and opens the circuit after warming up. Replacing one type with another is possible only if the technical parameters of a specific compressor model are observed.
- 🔹 Electromagnetic relays: work by drawing in the core with current and require strictly vertical installation.
- 🔹 Posistor (thermal) relays: use the property of a semiconductor to lose conductivity when heated, less sensitive to position.
- 🔹 Combination devices: combine start and protection functions in one housing, which is often found in compact models.
⚠️ Attention: When replacing the start relay, it is extremely important to observe the markings and orientation of the device. Installing the relay upside down or using an analogue with unsuitable operating current parameters can lead to burning of the compressor windings or constant humming without starting.
Visually, the starting relay is usually a black or gray plastic cube attached to the side or bottom of the compressor. Inside the housing there is a copper coil and moving contacts. Over time, the contacts can oxidize or burn, resulting in loss of contact and the inability to start the engine. Diagnostics often begins with checking the condition of these contacts and the integrity of the coil.
Protective thermal relay and its role
The second most important safety element is thermal relay (thermal protection). Its main task is to prevent the compressor from overheating and failure in emergency situations. If the starting relay is responsible for the start, then thermal protection ensures that the motor does not burn out during prolonged operation or during overloads.
Structurally, this device is a bimetallic plate that bends as the temperature rises. When the current in the motor circuit exceeds permissible limits or the temperature of the compressor housing becomes critical, the plate bends and opens the electrical circuit. This stops power supply to the motor. After cooling, the bimetallic plate returns to its original state, and the circuit closes again, allowing the refrigerator to try to start again.
Often the thermal relay is structurally combined with the starting relay into a single unit, especially in modern units. However, in older models, such as some series ZIL or Saratov, they could be separated. The critical parameter here is the protection response current: if you install a relay with a lower current, it will knock out even during normal operation; if it is large, it will not protect the engine from combustion. Therefore, when selecting a spare part, you need to look not only at the appearance, but also at the current marking.
Signs of a faulty thermal relay can be frequent cycles of turning the compressor on and off (the so-called "flashing" mode of operation) or complete failure of the device when the circuit does not close even in a cold state. In the latter case, the refrigerator simply will not respond to being plugged in, although the light inside will be on.
Thermoregulator: temperature control relay
The third type of device, which is often called a relay, although technically it is a thermostat or thermostat, is responsible for maintaining the temperature regime. It is he who “makes the decision” when to turn on the compressor for cooling and when to turn it off after reaching the set temperature. This is the main control element for the cyclic operation of the refrigerator.
The principle of operation of a mechanical thermostat is based on the expansion and compression of gas or liquid in a special capillary tube, which is placed in a cooled chamber. As the temperature rises, the pressure in the tube increases, affecting the membrane, which closes the relay contacts, starting the compressor. When cooling, the process occurs in the reverse order. In electronic models, this function is performed by thermal sensors and a control module, but the essence remains the same.
A malfunction of the thermostat leads to two main scenarios: either the refrigerator stops turning on and the food defrosts, or it works without interruption, freezing everything to the point of stone. In models with two compressors, for example, some Samsung or LG, there may be two thermostats - separately for the refrigerator and freezer compartments.
How to check the thermostat with a multimeter?
To check, you need to remove the thermostat and warm up its sensitive tube in your hands or put in warm water. In a cold state (if it is normally closed), the contacts should ring. When heated, an opening click should be heard and the circuit will be interrupted. If there is no click or the contact does not disappear, the part is faulty.
Replacing the thermostat requires care, especially when working with a capillary tube, which is easily damaged. It is also important to correctly set the temperature differential so that the compressor does not turn on too often, which shortens its life. In modern systems No Frost the thermostat is often supplemented with air dampers controlled by separate servo drives.
Defrost relays and timers in the No Frost system
In refrigerators with an automatic defrosting system No Frost or Full No Frost the defrost (defrost) relay plays a critical role. This device is responsible for turning on the heating element (heating element) in the freezer to melt the ice on the evaporator. Without this element working properly, the refrigerator will quickly become overgrown with ice and stop freezing.
This process can be controlled in two ways: through a mechanical timer-hour meter or through an electronic control module. In mechanical systems, a timer counts the operating time of the compressor and periodically switches contacts on the defrost circuit. In electronic systems, this is monitored microprocessorwhich reads the sensor readings and makes a decision to start defrosting.
Often an additional thermal relay (thermal fuse) is built into the defrost circuit, which opens the heating element circuit if the temperature in the evaporator becomes too high. This is fire protection. If such a relay burns out (opens), the heating element stops heating, the ice does not melt, and the evaporator becomes overgrown with a “fur coat,” blocking air circulation.
| Relay type | Main function | Typical sign of failure | Location |
|---|---|---|---|
| Starting | Starting the compressor engine | Clicks, humming without starting | On the compressor housing |
| Thermal | Overheat protection | Frequent shutdown or silence | In conjunction with the starter |
| Thermostat | Control temperature | Work without stopping or downtime | Inside the chamber or outside |
| Defrost | Turning on the defrosting heating element | Ice build-up in the chamber | In the evaporator zone |
Diagnostics of the defrost system requires an integrated approach. It is necessary to check not only the relay or timer itself, but also the integrity of the heating element, as well as the condition of the temperature sensors. In some models Bosch or Electrolux a malfunction of one sensor can block the operation of the entire system, and the refrigerator will go into error.
Fault diagnosis: how to understand that the relay has failed
You can determine which relay has failed by indirect signs of the operation of the refrigerator. Sound signals, compressor operating mode and temperature conditions in the chambers all give clues. However, accurate diagnosis often requires disassembling the back panel and using measuring instruments.
If you hear a loud click, followed by a humming sound from the compressor, and then another click and silence, this is a classic symptom of a malfunction starting relay or the compressor itself. The motor tries to start, the current increases, the thermal protection trips and turns off the power. After some time, the process is repeated. In this case, first of all, the starting device is checked.
If the refrigerator runs continuously without turning off for days, and the chambers are too cold (or, conversely, too warm if heat transfer is disrupted due to ice), the suspect stands in the direction of the thermostat or defrost relay. In the first case, the contacts are “stuck” in a closed state, in the second, the defrosting system does not work, and the ice blocks cooling.
☑️ Primary diagnostics of the relay
When visually inspecting the removed relay, you should pay attention to the color of the plastic and the condition of the contacts. Blackening, a burning smell, or melting of the housing indicates overheating and breakdown. It is also worth shaking the relay: if you hear the ringing of broken parts inside, the device definitely requires replacement.
Replacement and selection of analogues: practical recommendations
Replacing a relay in a refrigerator is a procedure accessible to a technician with basic skills, but requires compliance with safety precautions. Before starting any work, you must de-energize refrigerator by removing the plug from the socket. Working with electricity in the presence of moisture (condensation) is unacceptable.
To remove the relay, it is usually enough to remove the back cardboard or plastic cover covering the compressor. The starting device is often fixed on a bracket or simply placed on the contacts of the compressor. It is important to remember or photograph the wiring diagram so as not to confuse the contacts during assembly. Even seemingly identical relays from different manufacturers may have different contact layouts.
When searching for a spare part, focus primarily on the markings on the body of the old relay. Key parameters: voltage (220-240 V), frequency (50 Hz) and, most importantly, the power or current of the compressor. If an exact analogue cannot be found, you can select a universal relay, but its parameters must strictly correspond to the characteristics of the motor.
⚠️ Attention: Technical characteristics of compressors and compatible relays may vary between different manufacturers. Before purchasing a spare part, be sure to check the markings on the body of your old relay with the catalog data of the new one. Using an unsuitable component can damage the equipment.
After installing the new element and assembling the structure, you can perform a test run. In the first minutes of work, listen to the sounds: the even hum of the compressor without frequent clicks and vibrations indicates a successful repair. If the problem persists, perhaps the fault lies deeper - in the motor windings or the electronic module.
Frequently asked questions (FAQ)
Is it possible to start the refrigerator directly without a starting relay?
Theoretically, you can start an asynchronous motor by applying voltage directly to the working and starting relays windings, but doing this is strictly not recommended in domestic conditions. Without a shutdown relay, the starting winding will burn out in a few seconds, since it is not designed for long-term operation. It also poses a risk of short circuit and fire.
Why does a relay make a loud click?
The click is the normal sound of the mechanical contacts inside the relay opening or closing. A loud, distinct click every few minutes (during cyclic operation) indicates that the thermostat and starter are working properly. If clicks occur in a series and the compressor does not start, this is a sign of a malfunction.
How often do you need to change the relay in the refrigerator?
Relays are not consumables and do not require scheduled replacement. They last as long as the compressor itself if they operate normally. Replacement is made only in case of failure. The service life of a high-quality relay can be 10-15 years or more.
What is the difference between a relay for a refrigerator and a freezer?
The main difference is the temperature range of thermostats. The relays for the freezer are set to lower cut-out temperatures. Starting relays can be the same if the power of the compressors is the same, but thermostats are interchangeable only in rare cases.
Is it dangerous to change the relay yourself?
The main danger is electric shock if safety rules are not followed. The mechanical part of the replacement is simple, but it is important to choose the right part. If you are not confident in your abilities or do not know how to use a multimeter, it is better to entrust the repair to a professional so as not to damage the expensive compressor.