A sudden breakdown of a refrigerator often becomes an unpleasant surprise, especially when there are perishable foods left inside. One of the most vulnerable components responsible for starting the compressor is start-protection relay. It is this small element that supplies voltage to the motor windings and protects it from overloads at the time of start.
Understanding the operating principle of this device allows owners of household appliances to independently diagnose simple faults. If the refrigerator hums but does not start, or the compressor runs for only a few seconds and turns off, there is a high probability of failure of this particular component. In this article we will analyze in detail the design of the relay, the symptoms of its breakdown and the algorithm of actions to restore the unit's functionality.
It is important to note that modern models of refrigerators can be equipped with various types of starting devices, from simple induction to more complex electronic units. However, the basic protection and startup function remains unchanged for all modifications.
⚠️ Attention: All work on diagnosing and replacing electrical components of the refrigerator should be carried out only with the power completely disconnected from the network. Failure to comply with safety rules can lead to electric shock.
The operating principle and functions of the start-up relay
The main task of the device is to supply a short-term pulse to the starting winding of the compressor motor. At the moment of switching on, the refrigerator requires significant effort to move the piston group from its place. Start relay closes the starting winding circuit, creating the necessary torque, and opens it immediately after the rotor picks up speed.
The second, no less important function is thermal protection. Inside the case there is a bimetallic plate that reacts to rising temperatures. If the current in the circuit exceeds permissible limits or the engine begins to overheat, the plate bends and opens the contacts, completely de-energizing the compressor. This prevents melting of the windings and failure of the motor.
The actuation process occurs automatically and takes a fraction of a second. After the bimetallic plate has cooled down or the refrigerator has been turned on again, the startup cycle resumes. If the system is working properly, you can hear a characteristic click in the rear of the unit before the engine starts.
Main types of relays: induction, posistor and electronic
On the household appliances market you can find several types of start-protective devices. The choice of a specific type depends on the compressor model and year of manufacture of the refrigerator. The most common are induction and posistor relays, which differ in their internal structure and principle of operation.
Induction (or electromagnetic) relays operate due to the magnetic field created by the current in the winding. When the inrush current is high, the core retracts and closes the contacts. After the current decreases to operating values, the core returns to its original position under the action of the spring, opening the circuit. Such devices are often marked RT or RTP.
Posistor relays use a thermistor with a positive temperature coefficient of resistance. When cold, the crystal resistance is low, and current flows freely through the starting winding. Under the influence of current, the thermistor heats up, its resistance increases sharply, and the current practically stops. To restart such a relay, it takes time to cool down (usually 1-2 minutes).
- 🔌 Induction: reliable, but subject to sticking of contacts and mechanical wear of moving parts.
- 🔥 Posistor: have no moving mechanical parts, operate silently, but are sensitive to changes voltage.
- 💻 Electronic: installed in inverter compressors, controlled by a microprocessor and provide a smooth start without current surges.
You can determine the type of relay by its appearance and markings on the case. PTC devices are usually more compact and lighter, while induction devices may have a more massive body with a visible hole for the coil.
Typical symptoms of a malfunction and signs of burnout
Diagnosing a malfunction of the start-up relay does not always require disassembling the unit. Often the symptoms manifest themselves in the behavior of the refrigerator, which is impossible not to notice. The first and most obvious sign is the failure of the compressor to start when the lighting inside the chamber is on.
If you hear the motor trying to start, making a humming sound, but after a few seconds there is a click and silence sets in - this is a classic picture of thermal protection tripping. The relay gives an impulse, the engine does not start, the current increases, and the protection emergency shuts down the system. After some time, the cycle may repeat.
In some cases, a faulty relay may “stick” in the on position. This leads to the fact that the starting winding remains energized constantly, which causes severe overheating of the compressor and can lead to its combustion. Therefore, you cannot ignore strange sounds or lack of cold.
⚠️ Attention: If, after replacing the relay, the refrigerator stops starting again after a short time, the problem may not be in the new part, but in the compressor itself (turn-to-turn short circuit) or in low voltage in the network.
It is also worth paying attention to the appearance of the part. If during a visual inspection traces of burning are visible, melted plastic or the smell of burnt wiring is felt, Replacing the start relay it is necessary immediately. Operating a refrigerator with damaged electrical equipment is a fire hazard.
Diagnostics and checking the relay with a multimeter
Before going to the store for a new spare part, you need to make sure that the old part is faulty. To do this, you will need a regular multimeter (tester) set to resistance measurement mode (Ohm). The verification procedure is quite simple and does not require deep knowledge in electronics.
First you need to remove the relay from the compressor. It is usually mounted on three pins coming out of the motor and secured with a plastic frame or clip. Carefully disconnect the wires, having previously photographed their location so as not to confuse the contacts during assembly.
When checking a posistor relay in a cold state, the resistance between the main contacts should be low (several tens of ohms). If the device shows infinity (break) or, conversely, zero (short circuit), the part is faulty. For induction relays, the integrity of the coil and the mobility of the core are checked.
☑️ Checking the relay with a multimeter
Pay special attention to the contacts. If a black coating of oxide or carbon deposits is visible on them, this may interfere with the normal flow of current. In some cases, the contacts can be carefully cleaned, but given the low cost of the part, replacement is often more appropriate.
Parts compliance and compatibility table
When purchasing a new relay, it is important to consider not only the type of device, but also its compatibility with a specific compressor model. Different manufacturers use different mounting standards and electrical parameters. Below is a table to help you navigate the markings.
| Marking | Relay type | Compatibility | Features |
|---|---|---|---|
| RT-21, RT-23 | Induction | Refrigerators Atlant, Minsk | Vertical mount, coil |
| RTP-1, RTP-2 | Posistor | Biryusa, Saratov, Indesit | Horizontal mount, thermistor |
| PTC (Generic) | Posistor | Universal (Danfoss, Secop) | Requires selection according to motor power |
| 3-pin | Combined | Modern models | Built-in thermal protection |
If you do not If you find an exact analogue according to the article number, you can choose a universal relay. The main condition is the coincidence of the compressor power (indicated in Watts or Horse Power) and the contact configuration. An incorrectly selected part may burn out on the first start.
Where can you find the compressor power?
The engine power is usually indicated on a sticker located on the compressor itself at the bottom of the refrigerator. Look for the value in watts (W) or fractional numbers (such as 1/4 HP). If the sticker is not readable, you can focus on the volume of the fridge compartment: for models up to 250 liters, relays with 1/4 - 1/5 hp are usually suitable.
Instructions for replacing the start-up relay with your own hands
Replacing a part is a procedure available to any home craftsman. The main thing is to act consistently and not use excessive physical force, so as not to damage the compressor tubes. Before starting work, make sure that the refrigerator is disconnected from the power supply for at least 15-20 minutes.
Remove the rear protective panel (