Sudden stop of the refrigerator when the compressor tries to start, makes a loud click and goes silent, often indicates to a problem in the motor control circuit. Start relay is a critical component that ensures the start of the electric motor, and its failure is one of the most common causes of malfunctions of household appliances. If you notice that the unit hums but does not cool, or turns on and off cyclically, do not immediately panic and call a technician, as you can carry out diagnostics yourself.
Understanding the operating principle of this element will help save a significant amount on repairs and restore the device to functionality as soon as possible. Relay serves as a kind of switch that supplies voltage to the starting winding of the engine only at the moment of start, and then turns it off, allowing the compressor to operate normally. In this article we will analyze in detail the structure of the mechanism, the symptoms of its breakdown and a step-by-step verification algorithm.
Before starting disassembly, it is necessary to ensure safety and prepare a minimum set of tools. You will need a screwdriver, pliers and, preferably, a multimeter to accurately diagnose electrical circuits. Ignoring electrical safety rules can lead to electric shock or damage to working components of the refrigerator.
⚠️ Attention: Before starting any diagnostic or repair work, be sure to disconnect the refrigerator from the electrical network. Working with live electrical wiring is deadly.
Design and principle of operation of the starting relay
To effectively diagnose a malfunction, you need to understand exactly how this small but important component functions. Start relay is an electromagnetic a switch that responds to changes in current strength in the windings of an electric motor. When the refrigerator is turned on, the compressor rotor is stationary, and the current in the operating winding reaches its maximum values. This creates a magnetic field that draws in the solenoid core, closing the contacts of the start winding.
Once the engine reaches the required speed (usually 75% of the rated speed), the current drops, the magnetic field weakens, and under the influence of gravity or a spring the core returns to its original position, breaking the circuit starting winding. This cycle takes a fraction of a second, but it is what ensures the start of a powerful asynchronous motor. Modern models often use devices like PTC (posistors), which operate on the principle of changing resistance when heated, rather than mechanically opening.
Structurally, the relay is attached directly to the output contacts of the compressor or to the frame next to it. Inside the housing there are contacts, an inductor and a moving core. Critically important: in a relay with a mechanical breaker, the moving contact must move freely under the influence of gravity, so the installation position (marked with an up arrow) plays a decisive role. Violation of the orientation leads to sticking of contacts or impossibility of starting.
What is the difference between RTP and RTK relays?
RTP relays (posistor) do not have moving mechanical parts and work by heating a ceramic element, which increases the resistance. RTK (induction) relays use an electromagnetic core and a moving contact that opens when the current drops. PTC resistors are considered more reliable and durable.
Typical symptoms of a faulty start relay
Diagnostics begins long before removing the casing, if you carefully listen to the operation of the refrigerator. The most striking sign of failure starting relay is a characteristic click that repeats every few minutes. The compressor tries to start, hums for 2-5 seconds, then there is a click and there is silence. After some time, the cycle repeats, as the thermal motor protection relay cools down and supplies power again.
Another symptom may be a complete lack of reaction from the refrigerator when plugged in, while the light inside is on. If the engine is silent and does not make any sounds, the contacts inside the relay may have oxidized or become so burnt that the circuit is not closing at all. In rare cases, a faulty relay may not open the start winding, which leads to overheating of the compressor and its emergency shutdown by the thermal protector.
Visual inspection can also provide important clues. If you remove the protective cover and see traces of soot, melted plastic, or smell a burning smell coming from the relay, then replacing it is necessary in any case. Even if the device is still functioning somehow, its insulation is broken, which creates the risk of a short circuit.
- 🔊 Frequent clicks: The compressor hums for several seconds and suddenly turns off with a loud sound.
- 🌡️ Overheating of the housing: The back wall of the refrigerator or the compressor itself becomes excessive hot.
- 🚫 No starting: The engine is completely silent, although there is voltage at the input.
- 👃 Smell of burning: There is a smell of melted wiring or plastic in the area of the motor-compressor.
Dismantling and visual diagnostics of the part
To carry out a detailed check of the relay, it must be removed from the refrigerator. It is usually located in a niche at the lower rear of the unit, next to the compressor. First, remove the cardboard or plastic protective panel covering the engine compartment. Fastening can be done with latches or screws, so be careful not to damage the plastic.
After gaining access to the compressor, you will see a box placed directly on the motor contact group. Take a photo of the location of the wires before removal - this will help to avoid errors during assembly. Disconnect the connectors, having previously noted their color and markings, and remove the relay from the contacts. Often it is fixed with a metal bracket or plastic “ears” that need to be slightly pressed out.
Initial visual inspection allows you to identify obvious defects. Shake the relay near your ear: if you hear the sound of a detached contact or core inside, the part is definitely faulty. Inspect the housing for cracks, and the contact groups for black deposits or sparks. For relays of type RTK it is important to check the condition of the movable rod: it should not jam.
⚠️ Attention: When dismantling, be careful with the wires. Old insulation may crack and contacts may oxidize. Do not apply excessive force to the plastic fasteners, as they become fragile over time.
☑️ Removing the relay
Checking the relay with a multimeter: step-by-step instructions
The most accurate diagnostic method is to check the electrical resistance using a multimeter. Switch the device to resistance measurement mode (Ohm) for a range of up to 20 kOhm. First, check the continuity of the circuit between the input and output contacts. In the normal state (when the relay is lying on the table), the circuit can be open or closed depending on the type of device.
For induction relays (with a movable core) in a horizontal position, the contacts of the starting winding must be open. If you turn the relay strictly according to the markings (arrow up), the core will lower under the influence of gravity and close the contacts. If, when turning over, there is no click and the circuit does not close, it means that the mechanism is jammed or the contacts are burnt. The resistance between the contacts of the working winding should tend to zero.
When checking posistor relays (PTC) the situation is different. The resistance of the posistor itself in a cold state is usually from 15 to 50 Ohms. When voltage is applied, it should increase sharply to thousands of ohms, breaking the circuit. At home, it is difficult to check the dynamic change in resistance, so they often focus on static ones: if the multimeter shows infinity (open) or zero (short circuit) in a cold state, the relay is faulty.
| Relay type | Resistance in a cold state | Reaction to overturn | Probable malfunction |
|---|---|---|---|
| Induction (RTK) | 0 Ohm (closed) | Click, open | Contact sticking |
| Posistor (RTP) | 15-50 Ohm | Absent | Open or short circuit of the posistor |
| Combined | Depends on the circuit | Possible | Contact burnout |
| Any | Infinity | No reaction | Open circuit |
Replacement of the start relay and test run
If diagnostics confirm a malfunction, you need to purchase an analogue. Start relay selected strictly according to the compressor model or technical characteristics (engine power, type of refrigerant). There are no universal solutions, so it is best to look for the part by the catalog number indicated on the body of the old relay or in the technical documentation of the refrigerator.
The process of installing a new relay takes a few minutes. Install the device on the contact group of the compressor, observing the orientation (arrow UP or ⬆ should look straight up). Attach the retaining bracket or snap the plastic holders into place. Connect the wires in accordance with the previously taken photo or color coding of the terminals.
After assembly, do not rush to close the back panel. Plug in the refrigerator and listen to it start. The compressor should start working on the first try, without long hums and repeated clicks. Let the unit run for 10-15 minutes, monitoring the temperature of the motor housing and the absence of extraneous noise. If the startup was successful, install the protective cover in place.
Frequent errors in diagnostics and repair
One of the common mistakes is an attempt to “reanimate” the relay by cleaning the contacts with sandpaper. In modern devices, the contacts are coated with a special alloy (often containing silver), and mechanical cleaning only worsens the situation, accelerating burnout. In addition, this does not solve the problem of spring wear or changes in the properties of the posistor.
Also, novice craftsmen often ignore the orientation of the relay during installation. As mentioned earlier, for induction devices, the upside down position makes starting impossible, since the core cannot fall due to gravity. Always look for the marking UP or arrow on the body of the part.
Do not forget about checking the compressor itself. If replacing the relay did not help, and the engine still hums and knocks out the protection, the problem may lie in an interturn short circuit of the motor windings or jamming of the piston group. In this case, simply replacing the relay will not help; a more complex repair or replacement of the compressor will be required.
- ❌ Cleaning the contacts: It breaks the factory coating and leads to rapid re-failure.
- 🔽 Incorrect orientation: Installing the relay with the arrow pointing down blocks the operation of the mechanical breaker.
- 🔌 Ignoring wires: Bad contact in the connectors can simulate a broken relay.
- 🛑 Lack of compressor testing: If the motor is faulty, the new relay will burn out instantly.
Is it possible to start a refrigerator without a starting relay?
Theoretically, you can start an asynchronous motor by forcibly applying voltage to the starting winding, but this is absolutely impossible to do in a domestic environment. This requires precise control of timing and current, otherwise the compressor will burn out in a few seconds. In addition, without a relay, thermal protection will not work, which creates a fire hazard.
Why does the relay heat up during operation?
Slight heating is acceptable, but if the relay body becomes hot (cannot be touched), this indicates poor contact in the connections, a mismatch between the relay power and the engine, or a malfunction of the compressor itself (high consumption current). In this case, operating the refrigerator is dangerous.
How often do you need to change the starting relay?
The service life of a high-quality relay is designed for 10-15 years of operation. However, power surges, frequent power outages and overheating can shorten this period. A scheduled replacement is not required; the part is changed only when signs of malfunction appear.
Will a relay from another brand of refrigerator be suitable?
The brand of the refrigerator (Indesit, LG, Bosch) does not matter. It is important to comply with the compressor parameters (power, type of refrigerant R134a or R600a) and the mounting geometry. If the technical characteristics are the same, a relay from another manufacturer is quite suitable.