A sudden stop in the operation of a refrigeration unit or characteristic clicks, after which the compressor is silent, often throws owners of household appliances into a stupor. Many people immediately call a repairman or look for a new refrigerator, not suspecting that the problem may lie in a small part costing several hundred rubles. This part is called a starting relay, and it is responsible for starting the compressor engine, without which it is impossible to create cold.
Understanding the operating principle of this unit allows you not only to save on expensive repairs, but also to extend life refrigerator in general. If you ignore the signs of a relay malfunction, you can easily lead to the combustion of the motor windings, which will require a complete replacement of the compressor. Therefore, knowing how this component works and how it interacts with the rest of the system is a basic skill for any homeowner.
In this article we will analyze in detail the design of various types of relays, algorithms for testing them with a multimeter and the nuances of choosing a replacement. You will learn why old models with a posistor differ from modern induction systems, and how to correctly carry out diagnostics without damaging the remaining components of the unit.
Operating principle and main functions of the device
The main task of the starting relay is to briefly connect the starting winding of the compressor electric motor at the time of its startup. A refrigerator motor is an asynchronous motor that requires the creation of a rotating magnetic field to start rotating. The work winding produces only a pulsating field, so it needs the help of the starting winding, which is turned on for just a few seconds.
Once the engine reaches the required speed (usually about 75% of the rated speed), the relay should automatically break the starting winding circuit. If this does not happen, the current in it will increase to critical values, which will lead to overheating and burning of the insulation. Thus, starting relay performs a double function: it provides starting torque and protects the winding from overload in operating mode.
The process of opening the circuit is often accompanied by an audible click. In some designs, a separate thermal switch is responsible for this function, which is triggered when the bimetallic plate is heated by the current passing through the starting winding. In more modern models, this role is taken on by a posistor, which changes its resistance when heated.
⚠️ Attention: Frequent clicks of the relay without starting the compressor indicate that the engine is trying to start, but cannot turn the piston group. Long-term operation in this mode is guaranteed to disable the compressor.
Design features: posistor and induction relays
In household refrigerators, there have historically been two main types of starting devices, each of which has its own design features and operating logic. Understanding the difference between them is critical when selecting spare parts, since they are not always interchangeable.
The first type is induction (electromagnetic) relays. They are based on a coil connected in series with the working winding of the motor. When voltage is applied, current passes through the coil, creating a magnetic field that draws in the core and closes the contacts of the starting winding. At the same time, the normally closed contacts open, breaking the circuit after the current decreases (when the motor is running). Such devices often have a lever switching mechanism.
The second type is posistor (thermal) relays. They do not have moving mechanical contacts inside the relay itself. The circuit contains posistor a ceramic element, the resistance of which increases sharply when heated. When the refrigerator is turned on, the posistor is cold and passes current to the starting winding. The current heats it up, the resistance increases, and the current practically stops. To restart, the posistor requires time to cool down (usually 1-2 minutes).
- 🔹 Induction relays are more sensitive to voltage imbalances and require precise orientation during installation.
- 🔹 PTC models are more compact, cheaper to manufacture and less susceptible to vibrations.
- 🔹 The service life of posistors is often lower due to the degradation of the ceramic element during frequent switching cycles.
There are also combined devices where a starting relay and a thermal protection relay (RTK) are combined in one housing. They protect the motor from overcurrent and overheating, breaking the power circuit completely in emergency situations.
Why does a posistor relay click when cooling?
After turning off the power, the posistor remains hot. When cooling, microscopic changes in the structure occur inside the ceramic, which may be accompanied by a quiet crackling or clicking sound. This is normal and does not indicate a malfunction if the refrigerator itself is working correctly.
Typical symptoms of a faulty start relay
Diagnostics of a refrigerator often begins with analyzing the sounds it makes. A faulty relay rarely fails without a trace, and an attentive user can notice the first signs long before the unit completely stops.
The most striking symptom is that the compressor hums, but does not start, and after a few seconds there is a click and the hum stops. This indicates that the starting winding does not receive a pulse or the relay does not open the circuit, and the thermal protection is triggered. The motor tries to start, but to no avail.
Another sign is that the refrigerator turns on and works normally, but after a while there is a click and shutdown again. This may indicate sticking contacts or a malfunctioning thermal breaker. It is also worth paying attention to the appearance of the part: a blackened case, melted contacts or a burning smell clearly indicate the need for replacement.
Sometimes there is a situation when the compressor starts, but works intermittently or does not develop full power, which is why the temperature in the chamber does not build up. In this case, the contacts may be oxidized or burnt, creating a high contact resistance.
Diagnostics and testing with a multimeter
Before you go to the store for a new part, you need to make sure that it is faulty. To do this, you will need a multimeter (tester) and a minimum set of tools. The verification procedure is quite simple, but requires compliance with safety precautions.
First you need to turn off the power to the refrigerator and gain access to the compressor by removing the back panel. The start relay is usually mounted on the side of the compressor and secured with a clamp or latches. Carefully remove it, first remembering or photographing the position of the wires.
To check the posistor relay, shake it next to your ear. If you hear a rattling sound (like a broken ceramic element), the part is definitely faulty. Next, switch the multimeter to resistance measurement mode (Ohm) and test the contacts. The resistance must be either close to zero (short circuit) or correspond to the passport data. Infinite resistance (one on the screen) indicates an open circuit.
When checking an induction relay, it is important to evaluate the condition of the contacts. They must be clean, free of carbon deposits. The mechanical part must move freely. Check the coil for a break - the resistance should be within the normal range specified in the documentation.
☑️ Algorithm for checking the relay
Table of compatibility and replacement parameters
When selecting an analogue, it is important to consider not only the type relay, but also the power of the compressor, as well as the brand of the refrigerator. There are no universal solutions, although some models are suitable for a wide range of equipment.
Below is a table to help you navigate the markings and parameters. Please note that the current and power ratings must match or be slightly higher than the parameters of your motor.
| Relay type | Marking (example) | Compressor power | Compatible brands |
|---|---|---|---|
| Posistor | PTC 110/120 | 1/8 - 1/6 hp | Indesit, Ariston, Beko |
| Induction | RTK-1, RTK-2 | Up to 130 W | Atlant, Minsk |
| Combined | RTK-X-136 | 1/5 hp | Modern Atlanta |
| Universal | CSR-U2 | 4-6 A | Suitable for many models |
If you have not found an exact analogue by number, you can use universal starting relay. They are often equipped with a set of adapters for different types of connectors. The main thing is that the operating current of the universal relay overlaps the starting current of your compressor.
When purchasing, pay attention to the number of contacts. There may be two, three or more. You don’t have to use extra contacts, but all the necessary ones must be connected correctly according to the diagram.
Instructions for replacing the starting relay with your own hands
Replacing a part is a procedure that is accessible even to a beginner, if you act carefully. The main rule: all work is carried out only with the refrigerator completely disconnected from the network.
Remove the old relay by disconnecting the wires. Do not pull on the wires themselves, hold on to the connector blocks. If the wires are oxidized, clean their contacts or replace the terminals. Install the new relay in place, making sure that it is seated tightly and until it clicks (if provided for by the design).
Connect the wires according to the diagram, which is often marked on the body of the relay itself or the compressor. If the diagram is erased, take photographs of the disassembly process. After assembly, plug in the refrigerator and listen. The start-up should be confident, without prolonged buzzing.
⚠️ Attention: If after replacing the relay the situation has not changed (the compressor hums and does not start), the problem may be in the compressor itself (an interturn short circuit or a piston wedge) or in the wiring. Further diagnostics require the qualifications of a specialist.
Frequently asked questions and answers (FAQ)
Is it possible to start a refrigerator without a starting relay?
Theoretically, you can start the engine by artificially applying voltage to the starting winding, but the refrigerator will not be able to operate in this mode. Without a relay, the starting winding will burn out in a matter of seconds, since it is not designed for long-term operation. Operation without a working relay is strictly prohibited.
Why does a new relay burn out immediately after installation?
This can happen for several reasons: the power is incorrectly selected (the relay is weak for a given compressor), there are problems with the voltage in the network, or, most often, the compressor itself is faulty (difficult start-up, wedge). It is also possible that there is a short circuit in the wiring of the refrigerator.
How often do you need to change the start relay?
This part does not have a strict replacement schedule. It serves until it fails. On average, the resource is 5-10 years, but depends on the quality of electricity in the network and the frequency of switching on the refrigerator. It makes no sense to change it “for prevention.”
Does the room temperature affect the operation of the relay?
Yes, this is especially true for posistor models. In a very cold room, the posistor cools down faster, which can change the readiness time for restart. In a hot room, the cooling time increases, increasing the pause between startup attempts.