Starting the compressor in refrigerator is a complex physical process that requires precise coordination of electrical parameters. It is start relay that it takes on the role of a conductor who supplies a powerful impulse to the motor winding in order to overcome the inertia of rest. If this element fails, your refrigerator turns into a silent box, unable to maintain cold.
Understanding the principle of operation of this unit is necessary not only for household appliance repair specialists, but also for every owner who wants to extend the life of his unit. Relay protects the motor from overloads and ensures its smooth transition into operating mode after the starting jerk. Without it, the compressor may hum, click, but never start.
In this article we will analyze in detail the internal structure of various types of relays, methods for diagnosing them and the nuances of replacement. You will learn why characteristic clicks occur and how to distinguish a relay breakdown from more serious problems with the compressor. Electrical diagram The refrigerator is simple, but requires careful attention to detail.
Operation principle and purpose of the starting relay
The main task of the device is to briefly connect the starting winding of the engine to the AC mains. When the refrigerator is turned on, the compressor rotor is stationary, and to spin it up requires significantly more force than to maintain rotation. Starting winding creates the necessary phase shift that provides torque.
As soon as the motor shaft reaches approximately 75% of the rated rotation speed, the starting winding should be immediately disabled. If this does not happen, it will quickly overheat and burn out, since it is not designed for long-term operation. This is automatic shutdown the key function of the relay.
In addition, many modern models combine a starting and thermal protective relay in one housing. The second is responsible for emergency power shutdown in case of overheating of the windings or current overload. This double protection extends the life of an expensive compressor.
⚠️ Attention: If you hear frequent clicks when you try to start, but the compressor does not turn on, immediately unplug the refrigerator. Operating in this mode can lead to an interturn short circuit and complete failure of the motor.
There are two main types of devices that are radically different in design: electromagnetic (induction) and posistor. The former are controlled by current, the latter by the heating temperature of a special element. Switching mechanism They are implemented differently, which affects diagnostic methods.
The design of an electromagnetic (induction) relay
The design of the induction relay is based on using an electromagnetic coil and a moving core. Inside the housing there is a solenoid, which creates a magnetic field when current passes. This field draws in metal core, closing the contacts of the starting winding.
As soon as the engine starts, the current in the circuit drops to the operating value. The strength of the magnetic field becomes insufficient to hold the core, and under the influence of gravity (or a spring) it falls down, opening the contacts. Therefore, such relays are often called “crackers” because of the characteristic sound when the core falls.
It is important to consider the orientation during installation. Induction relays are sensitive to position in space, since the core must move freely under the influence of gravity. The housing usually has a marking UP or an arrow indicating the top position.
Why do induction relays fail?
A frequent cause of failure is sticking contacts or weakening springs. It is also possible that the solenoid coil may break, which leads to the absence of a magnetic field and the inability to close the start circuit.
A bimetallic thermal protection plate may also be located inside the housing. When overheated, it bends and opens the general power circuit. After cooling, the plate returns to its original state, and the cycle can repeat. Cyclic activation without starting the compressor is a sure sign of a problem.
How a posistor (thermal) relay works
In modern refrigerators such as Indesit, Ariston or LG, posistor devices are most often used. Their work is based on the property of a semiconductor element (posistor) to sharply increase its resistance when heated.
In a cold state, the resistance of a posistor is negligible, and it works like an ordinary conductor, passing current to the starting winding. The passing current heats the crystal, and when it reaches a certain temperature (Curie point), its resistance increases thousands of times. In fact, there is a circuit break.
The main difference from electromagnetic analogues is the absence of moving mechanical parts. There is nothing to stick or jam here, which increases the reliability of the unit. However, posistors have a peculiarity: after switching off, they require time (from 1 to 5 minutes) to cool down in order to pass current again.
If you try to turn on the refrigerator immediately after switching off, the compressor will not start until the posistor will cool down. This is a normal physical phenomenon, and not a malfunction. Recovery time depends on the ambient temperature and the design of the case.
Often the posistor is combined with a thermal protection relay into a single unit. In this case, when the compressor overheats, the bimetallic plate opens the circuit, and the current stops flowing even to the main motor. This provides comprehensive protection against overloads.
Fault symptoms and primary diagnostics
The breakdown of the starting relay can be determined by characteristic external signs. The most obvious symptom is that the compressor hums for 2-3 seconds, then a click is heard and the motor stops. After some time (when the thermal protection is triggered), the cycle repeats. This indicates that starting circuit does not open or close.
Another sign is complete silence when turned on, although the indicators are on. This may mean that the relay is not supplying voltage to the windings or that the thermal protection device has burnt out. It is also worth paying attention to the appearance of the part: blackened plastic or melted contacts indicate overheating.
For accurate diagnostics, a multimeter is needed. Before checking, be sure to disconnect the refrigerator from the power supply. Remove the compressor rear cover and carefully disconnect the relay connector. Visually inspect the contacts for oxidation or carbon deposits.
- 🔍 Check the integrity of the coil windings (for induction relays) - the resistance should be within normal limits and not broken.
- 🔥 Ring the contacts of the thermal relay - in a cold state they should ring (the resistance is close to zero).
- ⚡ Measure the resistance of the posistor - it should not be infinite or equal to zero in a cold state.
⚠️ Attention: Never measure the resistance or integrity of a live circuit. This can lead to failure of the multimeter and electric shock.
If a visual inspection and “diagnosis” do not reveal obvious defects, but the refrigerator does not start, the relay may lose contact pressure under load. In such cases, it only helps replacing the part with a known good one.
Instructions for replacing the starting relay
Replacing a relay is a procedure that is accessible even to a beginner, if you follow safety precautions. The main rule: all work is carried out only on completely de-energized equipment. Unplug the power cord from the outlet and move the refrigerator away from the wall.
Remove the protective plastic or metal cover at the back of the unit that covers the compressor. You will see a black cylindrical motor-compressor with a bunch of wires going to it. The relay is usually put directly on the three pins of the compressor.
☑️ Preparation for replacing the relay
Carefully remove the old relay. Notice how it sits on the contacts. Sometimes it is secured with a metal bracket or plastic clip. Do not pull on the wires - only hold the body of the part. Before installing a new element, compare the markings and the number of contacts.
Install the new relay in place, making sure that it is seated tightly until it stops. Connect the wires according to the photograph or diagram you took earlier. Make sure the connectors snap into place. Replace the compressor protective cover.
| Parameter | Inductive relay | Posistor relay |
|---|---|---|
| Operation principle | Electromagnetic | Thermal (resistance) |
| Moving parts | Yes (core) | No |
| Sensitivity to position | High | Low |
| Restart time | Immediately after the protection has cooled | Requires 1-5 minutes to cool down |
After assembly, turn on the refrigerator. Listen to the start-up sound: it should be confident, without long hums before the start. If the compressor starts working smoothly, you can consider the repair successful.
Frequent errors during repair and maintenance
One of the most common mistakes is an attempt to “reanimate” an old relay by stripping the contacts or bending the plates. In a refrigerator, this gives only a temporary effect, since the internal processes of degradation of materials have already started.
Another mistake is installing a relay of the wrong power or type. For example, installing an induction relay instead of a posistor relay (or vice versa) without changing the connection diagram can lead to the compressor burning out in a few minutes. Compatibility is a key factor.
Some users ignore the condition of the compressor itself. If the motor has high starting winding resistance or is mechanically jammed, even a new relay will not help it start. In this case, the relay will constantly click, trying to start the faulty unit.
- ❌ Trying to start the compressor bypassing the relay ("screwdriver") is dangerous to life and equipment.
- ❌ Using a relay from another refrigerator model without checking the electrical parameters.
- ❌ Ignoring blackening wires leading to the relay, which indicates poor contact.
⚠️ Attention: The characteristics of starting relays (operation current, cut-off time) may differ even for visually identical models. Always check the markings on the body of the new part with the technical documentation of your refrigerator.
Also, current surges can lead to welding of contacts or premature operation of the protection. To extend the life of equipment, it is recommended to use a voltage stabilizer.
Is it possible to repair a burnt-out relay yourself?
Theoretically, you can only replace the posistor or tighten the spring, but in practice this is not economically feasible. The cost of a new relay is low, and the reliability of the restored part will be questionable. It is better to completely replace the unit.
Why does the relay heat up during operation?
Slight heating of the housing is acceptable, especially for posistor models that operate by heating the element. However, if the relay becomes so hot that it cannot be touched, this is a sign of a compressor malfunction or poor contact in the circuit.
How often should the start relay be replaced?
The service life of the relay usually coincides with the service life of the compressor (10-15 years). No scheduled replacement required. They change it only when signs of a malfunction appear: problems with starting or characteristic clicks.
Does the tilt of the refrigerator affect the operation of the relay?
Yes, especially for induction relays. If the refrigerator is tilted too much, the core may not fall due to gravity and open the starting winding. For posistor relays, the slope is less critical, but also not desirable during long-term operation.