The refrigerator is one of the most important electrical appliances in the house, providing safety of products, and its sudden breakdown often becomes an unpleasant surprise. When the unit stops freezing or starts to work intermittently, the first thing that comes to the owner’s mind is calling a technician, but understanding the basic principles of the device’s operation can significantly save the budget. In the electrical circuit of modern refrigeration equipment, the key element for controlling the operation of the engine is start-protection relay, which is responsible for starting the motor and protecting it from overloads.
Many users do not even suspect the existence of this small but critical part until they encounter a characteristic clicking sound or complete failure of the equipment. It is this component that ensures a safe start compressorby opening the starting winding immediately after the engine reaches the required speed. Without the correct operation of this unit, the full functioning of the refrigeration unit is technically impossible, since the motor either will not start or will burn out from overheating in the first minutes of operation.
In this article we will look in detail at what exactly the relay in the refrigerator is for, how it is designed and why its serviceability directly affects the service life of all equipment. Understanding these processes will allow you to quickly diagnose the problem and make an informed decision on repairs.
The principle of operation of the starting mechanism
The main task of the starting relay is to briefly connect the starting winding of the compressor motor. The fact is that starting the rotor requires significantly more force than maintaining its rotation, and the standard operating winding is not enough for this. When the refrigerator is connected to the network, starting relay closes the circuit of the starting winding, creating the necessary torque, after which, when the engine reaches 75% of the rated speed, it automatically opens the contact.
This process occurs in a split second and is accompanied by a characteristic click, which many heard when operating a household appliance. technology. Depending on the design, opening can occur mechanically under the influence of gravity or an electromagnetic field, or thermally, due to the properties of the bimetallic plate. Induction relay they use a coil through which the current of the working winding passes, and when a certain current strength is reached, the core is retracted, opening the contacts of the starting circuit.
Why does the relay click when starting?
The click is the sound of the contacts opening inside the relay. In induction models, the core falls under its own weight, in posistor models it cools down and changes resistance. If the clicks are repeated frequently, but the cold does not occur, then the start-up does not occur.
It is important to note that without this mechanism the starting winding would remain on constantly, which would lead to its rapid burnout due to the high resistance and current load. Compressor in this mode of operation it would quickly fail, requiring an expensive replacement. Therefore, the health of the starting unit is the foundation for the stable operation of the entire refrigeration system.
Engine thermal protection functions
The second, no less important function of the unit is thermal protection, which prevents the compressor from failing due to overload or jamming. Inside the relay housing, in addition to the trigger mechanism, it is often located thermal relayworking on the basis of a bimetallic plate. This plate reacts to the strength of the current passing through the motor windings and to the temperature of the compressor housing itself.
If for any reason the current in the circuit exceeds permissible limits (for example, when trying to start a jammed piston or during voltage surges in the network), the bimetallic plate heats up and bends. This bending causes the electrical circuit to break and power to the motor is completely cut off. This emergency mode saves an expensive motor from burning out the windings, allowing it to cool down before the next attempt to start.
⚠️ Attention: If the thermal relay trips too often, this may indicate low voltage in the network or problems with the compressor itself. Do not ignore frequent shutdowns, as the constant cycles of heating and cooling can damage the contacts.
After cooling, the plate returns to its original position and the circuit closes again, giving the refrigerator the opportunity to restart. This cycle can be repeated several times until the cause of the overload is eliminated. It is the thermal relay that is the last line of defense, separating a simple repair from replacing the entire unit.
Types of starting devices
Modern and old models of refrigerators use various types starting devices, each of which has its own design features. Understanding the differences between them is important when selecting spare parts for repair, since they are not always interchangeable without modifications. The main types are induction, posistor and combined devices.
Induction (or electromagnetic) relays were widely used in Soviet and post-Soviet technology. Their operation is based on the retraction of the core by a coil, and they are position sensitive - they can only work in a strictly defined position, usually marked with an "UP" arrow. Posistor (or thermal relay) models have no moving mechanical parts in the starting circuit: a ceramic element (posistor) is used here, which, when heated by current, sharply increases its resistance, actually opening the circuit.
There are also combined options, where the starting function is implemented through a posistor, and thermal protection through a classic bimetallic plate. Such devices are more compact and reliable, since they have fewer mechanical elements subject to wear. When choosing a replacement, it is important to pay attention not only to the appearance, but also to the electrical characteristics indicated on the marking.
Symptoms of a relay malfunction
Diagnostics of a faulty start-up protection device often does not require complex equipment and can be carried out visually or auditorily. The most common sign of a breakdown is when the compressor hums and tries to start, but after a few seconds a click is heard and the motor stops. After some time, the cycle repeats, which indicates that the thermal protection has tripped or it is impossible to break the starting circuit.
If the relay is “stuck” in the closed state, the starting winding may burn out, which will lead to more serious consequences. In some cases, you may hear a cracking sound or see sparking inside the relay housing if you remove the protective cover. Also, a malfunction may be indicated by the complete lack of reaction of the refrigerator to being plugged into the network, although there is voltage in the socket.
- 🔊 The compressor hums for 3-5 seconds, then clicks and goes silent, after which there is silence.
- 🔥 Strong heating of the relay housing or the appearance of the smell of bare insulation.
- 🔌 The refrigerator does not turn on, the indicators are on, but the motor is silent.
- ⚡ Frequent operation of the circuit breakers in the electrical panel when the refrigerator is turned on.
It is important to distinguish between the symptoms of a relay failure and a failure of the compressor itself. If, when the relay is turned off and power is supplied directly (which only a specialist should do), the motor starts, then the problem is in the control element. Otherwise, if the motor hums even without a relay or does not start when fed directly, the problem may be in the mechanical part of the engine.
Comparison table of relay characteristics
For a deeper understanding of the differences between types of devices, we provide a comparison table. It will help you determine what type of device is installed in your model and what to look for when looking for an analogue.
| Characteristics | Inductive relay | Posistor relay | Combined |
|---|---|---|---|
| Principle actions | Electromagnetic | Thermal (posistor) | Combined |
| Presence of moving parts | Yes (core, contacts) | No (in the starting circuit) | Yes (in thermal protection) |
| Sensitivity to position | High (strictly vertical) | Low (any orientation) | Depends on the model |
| Service life | Medium (contact wear) | High | High |
It is worth noting that modern manufacturers are increasingly switching to the use of posistor and combined circuits, since they are less susceptible to vibrations and temperature changes. However, in older models Indesit, Atlant or Biryusa there are still often classic induction options that require careful installation.
Checking and replacing the device
The process of checking the relay begins with completely disconnecting the refrigerator from the power supply. This is a mandatory safety condition, since work is carried out with conductive elements. After removing the rear protective panel and the compressor casing, you must carefully remove the relay from the engine contact group, having previously memorized or photographed the connection diagram.
Visual inspection often reveals obvious defects: melted plastic, blackened contacts, traces of soot or destruction of the housing. If there is no external damage, you can use a multimeter in continuity mode. For induction relays, check the resistance of the coil and the mobility of the core, and for posistor relays, check the resistance of the ceramic element itself (it should be within 10-50 Ohms when cold). compressor
☑️ Relay diagnostics
Replacement is carried out in the reverse order of removal. It is important to ensure that the contacts fit tightly and the device is correctly oriented relative to the ground if it is an induction type. After installing the casing and turning on the device, you should carefully listen to the first startup cycle: it should go through smoothly, without prolonged buzzing and repeated clicks.
⚠️ Attention: Never try to start the compressor directly, bypassing the thermal relay, even for a short-term check. This can lead to instant burning of the windings and a fire hazard.
Frequently asked questions and answers
Is it possible to repair a burnt out relay with your own hands?
In most cases, repairing a relay is impractical. If the contacts are burnt or the posistor has lost its properties, it is almost impossible to restore their factory characteristics. Attempts to clean the contacts give only a temporary effect, after which the breakdown recurs. It is easier and safer to buy a new element, the cost of which is usually low.
Why does the relay heat up during operation?
Slight heating of the housing is acceptable, since currents pass inside. However, if the relay becomes so hot that it is impossible to touch it, this indicates poor contact at the junction with the compressor or a malfunction of the motor itself, causing overcurrent.
How to choose an analogue if the original is not on sale?
The key parameters are the power of the compressor (indicated on the tag, for example, 1/4 hp or 1/3 hp) and refrigerant type. The matching of the seats and the location of the contacts is also important. Universal relays often come complete with adapters for different models.
Does frequent opening of the door affect the operation of the relay?
Indirectly - yes. Frequent opening of the door leads to an increase in the temperature inside the chamber, which is why the compressor is forced to turn on more often and work longer. This increases the number of on/off cycles of the relay, accelerating the wear of its contacts and thermal protection.