A modern refrigerator is a complex electromechanical unit in which each element performs a strictly defined function to maintain a given temperature regime. Many owners of household appliances do not even think about the internal processes until a breakdown occurs, when the products begin to deteriorate and the compressor stops starting or runs idle. The key component that ensures the start and safe operation of the motor is starting relay, which is often the first to fail.
It is this small unit that is responsible for supplying voltage to the motor windings at the moment of switching on and subsequent opening of the circuit after the required speed has been reached. Without a working relay, starting the compressor is physically impossible, since a single-phase asynchronous motor does not have sufficient starting torque to rotate the rotor independently. Understanding the operating principle of this unit will help you quickly diagnose the problem and avoid an expensive call to a technician for a simple replacement of the part.
In this article we will look in detail at why the relay is critical for a refrigerator, what types of these devices exist and how to determine their malfunction by external signs. You will learn how induction mechanisms differ from posistor mechanisms, and receive step-by-step instructions on how to safely replace the element. Attention to detail during diagnostics will save time and money by bringing the equipment back to life as soon as possible.
The principle of operation of the trigger mechanism in the system cooling
The fundamental task of the starting relay is to provide short-term connection to the starting winding of the compressor motor. When the refrigerator is connected to the network, the motor rotor is stationary, and to spin it up requires significantly more force than to maintain rotation. Starting winding creates the necessary phase shift and additional torque, but it is not intended for long-term operation and must be turned off immediately after the motor reaches approximately 75% of the rated speed.
The process occurs automatically and takes a split second. As soon as the current in the circuit reaches a certain value or passes a specified time interval, the relay mechanism opens the contacts, cutting off the starting winding. Further operation of the motor is carried out only through the main working winding. If this step is skipped or delayed, the engine begins to hum, overheats and may burn out due to lack of torque.
In parallel with the starting function, in many designs a relay is integrated thermal protection relay. It monitors the current consumed by the compressor. In the event of jamming of the piston group or an interturn short circuit, the current increases sharply, heating the bimetallic plate inside the relay. The plate bends and opens the power circuit, preventing fire in the windings or failure of the refrigerator wiring. This dual function makes the device an indispensable safety element.
⚠️ Attention: Frequent clicks of the relay when trying to start the compressor may indicate not only a breakdown of the relay itself, but also a malfunction of the motor or a drop in voltage in the network. Do not ignore repeated attempts to start, as this can finally finish off a working engine.
Design features and types of starting relays
In household refrigeration equipment, there have historically been two main types of starting devices, each of which has its own technical features and operating principles. The most common ones are induction-dynamic relayswhich are often called “tablets” because of their shape and location on the compressor. Inside such a device there is an inductor and a movable core with contacts. When current is applied, the magnetic field raises the core, closing the contacts of the starting winding, and when the engine accelerates, the core falls under the influence of gravity, opening the circuit.
The second type is positor (thermal) relayswhich are considered more modern and reliable. There is no mechanical moving element in their design. Instead, a semiconductor crystal (posistor) is used, which at room temperature has low resistance and passes current to the starting winding. When current passes, the crystal heats up, its resistance increases sharply, and the current almost completely stops, which is equivalent to breaking the circuit. Such relays operate silently and are less sensitive to vibrations.
It is important to note that different models of refrigerators, be it Indesit, Atlant or LG, can be equipped with different types of relays depending on the year of manufacture and compressor power. There are no universal solutions, since the current characteristics of motor windings vary. Installing an unsuitable relay can result in the engine either not starting or running with overload, constantly turning on thermal protection.
Can a universal relay be used?
Universal relays with a set of adapters exist, but they are a temporary solution. Their current characteristics may not match the original, which will shorten the life of the compressor. It is better to look for the original part number.
Fault symptoms and initial diagnostics
You can determine that the relay has failed by the characteristic signs that appear immediately after turning on the refrigerator. The most obvious symptom is the compressor not starting when the lighting inside the chamber is on. The engine may make a dull humming sound as it tries to start, but after a few seconds there will be a loud clicking sound and the humming will stop. After some time, the cycle will repeat, as the thermal protection cools down and tries to turn on the engine again.
Another sign is a complete failure of the equipment to work, when the light does not light up and no sounds are heard, however, this more often indicates a problem with the wiring or socket. If the lamp is on, but the compressor is silent, perhaps the contacts inside the relay have oxidized or burned so much that they have stopped conducting current. In some cases, a faulty relay may “stick” when turned on, which is why the starting winding does not turn off, which leads to rapid overheating and a characteristic smell of burnt insulation.
For an initial check, you can gently shake the removed relay near your ear. If a rattling sound is heard inside, similar to the rattling of bolts in a can, it means that the internal elements are destroyed or torn off. This is a 100% sign that replacement is needed. However, the absence of sound does not guarantee serviceability, since the contacts may simply be burnt, but the mechanical part is intact.
- 🔊 The compressor hums for 5-10 seconds, followed by a click and silence.
- 🔥 Noticeable heating of the relay housing or the appearance of a burning smell in the compressor area.
- 🔌 When you turn on the refrigerator, the circuit breaker (RCD) in the panel is knocked out.
- 🧊 The refrigerator compartment does not cool, although the indicators on the panel may light up.
Table for comparing the characteristics of relays of different types
To better understand the differences between the devices that you may encounter during repairs, it is worth turning to a comparative analysis. Different manufacturers use different engineering solutions, and knowledge of these nuances will help you choose the right spare part. Below are the main parameters by which the components differ.
| Comparison parameter | Induction (Electromagnetic) | Posistor (Thermal) | Electronic (Rarely) |
|---|---|---|---|
| Principle of operation | Magnetic field and gravity | Change of resistance when heated | Control chip |
| Sensitivity to tilts | High (must stand vertically) | Absent | Absent |
| Activation resource | Average (mechanical wear) | High (no rubbing parts) | Very high |
| Replacement cost | Low / Average | Average | High |
As can be seen from the table, positor relays they benefit from reliability and stability to spatial position, which makes them preferable for modern models. However, induction mechanisms are still widely found in old refrigerators and some budget series. Electronic launch control options are less common and are usually part of the overall refrigerator control board, rather than a separate hinged unit.
Step-by-step instructions for replacing the start relay
Replacing the relay is one of the few operations that the user can perform independently without special equipment, if safety precautions are followed. The first and most important step is to completely disconnect the refrigerator from the electrical network. Don’t just turn off the button, but unplug the cord from the outlet, since you will have to work with live parts.
Next you need to gain access to the compressor. In most models, this requires moving the refrigerator away from the wall and removing the back metal cover at the bottom of the case. Sometimes it is necessary to remove the plastic casing covering the motor-compressor itself. Be careful not to jerk the copper tubes sharply, they may burst, which will lead to a freon leak and costly repairs.
Locate the start relay. It is a plastic box placed on three pins coming out of the compressor. Carefully remove it, after photographing the position of the wires. Disconnect the wires, remembering or marking which one was connected where. Install the new relay in the reverse order, tightly fitting it onto the compressor contacts and connecting the wires in accordance with the diagram.
☑️ Algorithm for replacing the relay
⚠️ Attention: If oxide or carbon deposits are visible on the contacts of the new relay or on the pins of the compressor, be sure to clean them with fine sandpaper or a file before installation. Poor contact will lead to sparking and repeated failure.
Frequently asked questions and important operating nuances
Owners often wonder why the relay burns out. The main reason is the natural wear of the contacts from constant micro-discharges every time you turn it on. However, there are also external factors, such as power surges or frequent power outages when they try to turn on the refrigerator immediately after the light comes on. The compressor takes time (about 5-10 minutes) to equalize the pressure in the system, and restarting without a pause creates a critical load on the relay and motor.
It is also worth mentioning the temperature regime. If the refrigerator is installed close to a wall or in a niche without ventilation, the compressor overheats. The thermal relay will constantly trip, turning off the motor, which ultimately leads to degradation of the materials of the protective device itself. Ensuring free access of air to the capacitor and motor is the key to a long life not only of the relay, but also of the entire unit.
Sometimes users try to “reanimate” an old relay by opening the case and cleaning the contacts. Do this strongly not recommended. Factory calibration of trip current and trip time is violated when opened. Such a relay may not turn off the starting winding in time, which will lead to the burning of an expensive compressor. The cost of a new part is not commensurate with the risk of losing the entire refrigerator.
Is it possible to install a relay from another refrigerator?
Only if the technical characteristics match, in particular the operating current and type of switching. Visually they may be similar, but the internal calibration is different. It is better to look for the part by the catalog number indicated on the body of the old relay.
Why does the new relay immediately burn out after installation?
This indicates a more serious problem, most likely the compressor itself is faulty (turn-to-turn short circuit) or there are problems with the wiring. In this case, simply replacing the relay will not help; motor diagnostics are required.
How long can a refrigerator with a faulty relay work?
In fact, it will not work. The compressor will either not start at all, or will work intermittently with constant shutdowns due to thermal protection. Operation in this mode is a fire hazard.
Is it necessary to vacuum the system when replacing the relay?
No, replacing the starting relay occurs from the side of the electrical contacts and does not violate the tightness of the freon circuit. Evacuation and refilling are required only when repairing tubes or replacing the compressor itself.