Sudden silence in the kitchen, interrupted only by the quiet hum of a compressor that never starts, is often the first signal of a serious breakdown. At this moment, the refrigerator stops cooling, food begins to spoil, and the owner is faced with the need for urgent diagnostics. One of the most common causes of motor failure is the failure of starting relay a small but critically important component of the electrical circuit.
It is this unit that is responsible for starting the engine, supplying the necessary impulse to the starting winding in the first fractions of a second of operation. Without the correct functioning of this element, the compressor either hums without starting to rotate, or makes characteristic clicks and is turned off by protection. Understanding how it works refrigerator start relaywill allow you to independently determine the nature of the breakdown and, perhaps, avoid an expensive call to a technician.
In this article we will analyze in detail the internal structure of various types of relays, consider the physical principles of their operation and provide a step-by-step algorithm for checking functionality. You will learn why some models make loud clicks, how posistor systems differ from induction ones, and how to choose the right replacement for your unit.
Main purpose and principle of operation
The functionality of the starting relay is to briefly connect the starting winding of the compressor motor to the electrical network. When the refrigerator is turned on, the motor rotor is motionless, and to create the initial torque, a powerful impulse is required, which is provided by the starting winding. Starting relay automatically supplies voltage to this winding, and then, when the engine reaches the required speed, disconnects the circuit.
The process occurs in fractions seconds, but the successful launch of the entire refrigeration system depends on it. If the relay does not work or sticks, the compressor will not be able to go into operating mode or, worse, will burn out due to overheating of the windings. In modern models, such as Indesit or Atlant, this process is often accompanied by a characteristic sound, which should not be confused with the noise of the compressor itself.
⚠️ Attention: If, after clicking the relay, the compressor hums, but does not start within 3-5 seconds, immediately disconnect the device from the network. Holding the starting winding energized for a long time without rotating the rotor is guaranteed to lead to an interturn short circuit and expensive motor repairs.
The key element here is the current difference or change in resistance that fixes the device. Depending on the design, the relay can respond to an increase in current in the main winding or to a change in the temperature of a special element. The critical parameter is the contact opening time, which must strictly correspond to the motor's passport data. Violation of this time interval leads either to the engine not being allowed to reach operating speeds, or to its operation in an inefficient mode.
Design of induction (electromagnetic) relay
Induction relays, often called “tablets” because of their characteristic shape, are a classic solution for old-style refrigerators and many modern budget models. Inside the plastic case there is a coil through which the current of the main winding of the motor passes. When current passes through the coil, a magnetic field is created that draws in the movable core.
A contact is mechanically attached to this core, which closes the starting winding circuit. At the moment of start, the current in the motor is maximum, the magnetic field is strong enough to hold the core in the upper position, providing power to the starting winding. As the rotor accelerates, the current drops, the magnetic field weakens, and under the influence of gravity (or a spring in some modifications), the core drops, opening the contacts.
- 🔌 Inductor — creates a magnetic field proportional to the current in the circuit.
- ⚙️ Movable core —an actuator that moves under by the action of a magnet.
- 🔘 Contact group —provides a physical connection of circuits, often made of silver or an alloy with a high resource.
- ⚖️ Spring or counterweight —returns the mechanism to its original position when the current drops.
A feature of such devices, often found in technology Birusa or Orsk, is their dependence on position. They must be installed strictly in a certain position, indicated by the arrow on the body, otherwise the core will not be able to move freely under the influence of gravity. Violation of the orientation leads to the fact that the relay either does not close or does not open in time.
Design and operation of a posistor (thermal) relay
More modern refrigerators, including the popular series LG i Samsung, are equipped with posistor starting relays. Their work is based on the use of a part called a posistor - a semiconductor element whose resistance increases sharply when heated. This allows you to eliminate moving mechanical parts, which increases the reliability of the unit as a whole.
When voltage is applied to a cold posistor, its resistance is minimal, and it passes current through the starting winding, starting the engine. The passing current causes the crystal to heat up. Having reached a certain temperature, the posistor abruptly increases its resistance almost to infinity, essentially breaking the starting winding circuit. After cooling, which takes several minutes, the resistance drops again, and the relay is ready for a new cycle.
The main advantage of this circuit is the absence of rubbing parts and sparking, which reduces electromagnetic interference. However, posistors also have weaknesses: they are sensitive to voltage surges and require time to cool down before restarting. If you try to turn on the refrigerator immediately after turning it off, the posistor is still hot and will not allow current to pass through, so the compressor will not start.
| Comparison parameter | Inductive relay | Posistor relay |
|---|---|---|
| Operating principle | Electromagnetic | Thermal (change in resistance) |
| Moving parts | Yes (core, contacts) | No |
| Dependence on position | High (vertical needed) | Absent |
| Restart time | Instantly (after the bimetal has cooled) | Requires 3-5 minutes for cooling |
Typical symptoms of a faulty starting device
Diagnostics begins with carefully listening to the operation of the unit. The most obvious sign of a malfunction is the cyclic repetition of the starting process: there is a loud click, the compressor begins to hum, trying to start, then another click follows, and the motor goes silent. After a few minutes or seconds, the cycle repeats. This indicates that the relay is trying to start the engine, but cannot hold contacts or break the circuit.
Another symptom may be a complete lack of response from the compressor when the refrigerator is turned on. The light inside is on, the fan (if there is one) is noisy, but the motor is silent. In this case, the relay is often to blame because it simply does not close the starting winding circuit. It is also worth paying attention to the appearance: if the relay has traces of burning, melted plastic or the smell of burnt insulation, its replacement is necessary without additional inspection.
⚠️ Attention: Do not confuse the clicks of the start relay with the clicks of the thermostat. The thermostat clicks less frequently, usually when the set temperature is reached, and this is accompanied by the compressor turning on or off for an extended period. The relay clicks frequently and rhythmically when trying to start.
Sometimes a malfunction can manifest itself in the form of knocking out plugs or circuit breakers in the electrical panel when the refrigerator is turned on. This indicates a short circuit inside the relay or breakdown of the winding insulation. In such cases, operating the device is dangerous and requires immediate disconnection from the power supply.
☑️ Primary diagnostics of the relay
Step-by-step instructions for diagnostics and replacement
To carry out diagnostics, you will need to remove the relay from the compressor. Be sure to unplug the refrigerator from the power supply first! Remove the rear protective panel, locate the compressor and carefully disconnect the relay connector. Usually it is simply put on the three contacts of the motor and secured with a bracket or plastic latches.
First, carry out a visual inspection. Shake the relay near your ear: if a clear knocking sound of a detached core or contacts is heard inside, the part is faulty. Next, take a multimeter and set it to resistance measurement mode (Ohms). Check the integrity of the coil and contacts. For induction relays, the coil resistance should be low (several Ohms), and the contacts in a certain position should ring.
Normal resistance of an induction relay coil: 10-30 OhmsThermistor resistance in a cold state: 10-50 Ohms
Resistance of the posistor in a hot state: > 1 MOhm
If the test confirms a malfunction, you need to purchase an analogue. You need to search by the markings on the body (for example, RT-1, P-3, MP-2). Installation of a new part is carried out in the reverse order of removal. Make sure that the contacts are tightly placed on the pins of the compressor, and the relay itself is fixed in the correct position.
What to do if the new relay does not fit the fastenings?
Sometimes manufacturers change the design of connectors. In this case, you can carefully re-solder the wires from the old relay to the new one, observing the color markings and connection diagram. The main thing is not to confuse the starting and operating windings, otherwise the motor will burn out instantly.
Frequently asked questions and important operating nuances
Many owners wonder whether it is possible to temporarily start a refrigerator without a relay. Theoretically, this is possible by manually applying voltage to the starting winding, but in practice this is extremely dangerous and is not recommended without special skills. Incorrect pulse duration will cause the motor to burn out. In addition, modern protection systems can block the operation of the compressor if there is no signal from the relay.
Another important aspect is compatibility. There are no universal relays. A device rated for 1/5 HP will not fit a 1/3 HP compressor. The difference in current will either cause the contacts to stick or make it impossible to start. Always check the technical documentation or markings on the old element.
⚠️ Attention: Technical characteristics of compressors and relays may vary depending on the year of manufacture and the specific modification of the refrigerator. Before purchasing a spare part, always check the markings with the original or consult the catalogs of the spare parts manufacturer for your model.
Regular maintenance, including cleaning the capacitor and checking the voltage in the network, will extend the life of not only the relay, but also the entire compressor. Voltage surges are the main enemy of refrigerator electrics, so using a stabilizer or at least a surge protector will be a wise investment in the longevity of the equipment.
Questions and answers (FAQ)
Is it possible to repair the starting relay or just replace it?
In 95% of cases, the relay must only be replaced. Disassembling the case often leads to a violation of the tightness and geometry of the internal parts. PTC resistors are generally monolithic elements. An attempt to clean the contacts of an induction relay gives a temporary effect, but the resource of such a unit is calculated in hours.
Why does a new relay make a different sound when operating?
The sound depends on the design and manufacturer. Induction relays may hum or click louder than the original due to differences in build quality or core material. If the refrigerator starts and cools, and the sound is not a sign of vibration of the case, this is acceptable.
How to distinguish a burnt relay from a faulty compressor?
You need to ring the motor windings with a multimeter. If the resistance between the motor contacts shows an open (infinity) or a short to the housing, the problem is in the motor. If the windings are intact, but there is no start, the relay or wiring is to blame.
Does the room temperature affect the operation of the relay?
Yes, especially for posistor models. In a very cold room (below +10°C) the relay may not work correctly or take longer to warm up. Induction relays are less sensitive, but the viscosity of the oil in the compressor in the cold also makes it difficult to start.