You hear a loud click, followed by a hum, but the compressor still does not start, or the refrigerator is silent, although there is voltage in the network is there? In 80% of cases, the cause lies in a small but critical element of the electrical circuit, often called the start relay. This device is responsible for starting the compressor engine, providing the necessary torque to start the cooling system. Without a working relay, a modern household refrigerator turns into a useless box, and food begins to deteriorate.
Many owners of household appliances perceive starting relay as complex electronics, inaccessible to understanding without a deep knowledge of physics. In fact, the principle of its operation is based on simple mechanics and the basic laws of electrical engineering. In this article, we will analyze in detail how exactly this component controls the start of the motor, why it fails, and whether it is possible to carry out diagnostics yourself without calling a technician.
Understanding the structure of the refrigerator helps not only at the time of breakdown, but also when choosing new equipment. Knowing that compressor and its piping are the heart of the unit allows you to be more careful in its operation. If you notice that the refrigerator has started to work incorrectly, you cannot ignore this, since a malfunction of one element can lead to the burning of an expensive engine.
The principle of operation of the start relay
To understand what is a relay in a refrigerator, you need to consider the process of starting the engine. A refrigerator compressor is an electric motor with a squirrel-cage rotor, which has two windings: the main (working) and additional (starting) windings. At the moment the voltage is turned on, no torque appears on the rotor, so a short-term impulse is required through the starting winding to move it.
It performs exactly this task starting relay. Classic models use a device with a posistor (thermistor). When voltage is applied, the posistor resistance is low, current flows freely through the starting winding, creating a magnetic field to start the rotor. Within a split second, the posistor heats up from the passing current, its resistance increases sharply, and the starting winding circuit actually breaks. The engine continues to operate on the main winding.
There are also induction-type relays, where the contacts open under the influence of a magnetic field created by the current in the working winding. When the engine speed reaches the nominal speed, the current drops and the contacts open. Relay malfunction often manifests itself precisely at the stage of opening or closing: if the contacts are “stuck”, the engine will hum and overheat, and if it does not close, the motor will not start at all.
It is important to note that the switching process occurs hundreds of times a day, which leads to natural wear of the contacts or a change in the properties of the posistor. That is why The service life of the starting relay is usually 5-7 yearsafter which the probability of failure increases sharply. Modern inverter refrigerators operate on a different principle, but in classic models the relay remains a key element.
Main symptoms of a malfunction
Diagnostics begins with carefully listening to a working (or trying to work) unit. If you hear a characteristic click, followed by a buzzing sound lasting 3-5 seconds, and then another click and silence, this is a sure sign of a problem. The compressor tries to start, but starting device cannot switch the windings correctly or hold the contacts.
Another alarming symptom is the strong heating of the compressor housing in the lower part of the refrigerator. If the motor hums but does not start, the current in the windings increases, causing overheating. In such cases, a thermal protection relay is activated, which breaks the circuit to prevent fire or melting of the insulation. After cooling, the cycle repeats.
- 🔊 Frequent clicks: Periodic sounds of turning on and off every few minutes indicate attempts to start.
- 🔥 Heating housings: The bottom of the refrigerator (where the motor is located) becomes hot to the touch, although there is no cold inside.
- ❄️ Lack of cold: The food in the chambers begins to deteriorate, the ice in the freezer melts, despite the working light and fan (if there is one).
- ⚡ Knocking out plugs: In rare cases, a short circuit inside the relay can lead to the operation of circuit breakers in the electrical panel.
⚠️ Attention: If the compressor hums for more than 10-15 seconds in a row and does not start, immediately unplug the refrigerator. Prolonged operation in this mode (“humming on a jammed shaft”) can (burn out) the motor windings, which will lead to an expensive replacement of the entire compressor.
Sometimes the symptoms can be vague. For example, the refrigerator works, but the cycles become too short. This may indicate that thermal protection the relay inside worked ahead of time due to a violation of the calibration of the bimetallic plate. In this case, the unit does not have time to reach the desired temperature, but already turns off.
Types of starting relays and their differences
There are several types of starting devices on the household appliances market. Understanding the differences between them is necessary for the correct selection of spare parts. The most common type is POSITOR relay. It is a plastic case, inside of which there is a tablet made of ceramic material (posistor) and contacts. Such devices are cheap, reliable and do not have moving mechanical parts subject to wear.
The second type is inductive (electromagnetic) relays. They were more often found in Soviet refrigerators (Atlant, Zil, Biryusa) and some older foreign-made models. Inside such a device there is a coil and a movable core with contacts. When starting, the current is high, the magnetic field draws in the core, closing the starting circuit. When the motor accelerates, the current drops, and the core falls under the influence of gravity and the spring, opening the circuit.
| Characteristics | Posistor relay | Induction relay |
|---|---|---|
| Principle of operation | Change in resistance when heated | Magnetic field and gravity |
| Location | Any (often on the side) | Strictly in a certain position (marked with an up arrow) |
| Resource | High (no rubbing parts) | Medium (contact wear) |
| Sensitivity | To voltage surges | To tilts and vibration |
Modern combined relays can combine both the starting function and thermal protection. In such models, both a posistor and a bimetallic protection plate are located in one housing. When purchasing a spare part, it is important to pay attention to the markings and power of the engine for which the device is intended. Universal relays does not exist: a device designed for a powerful compressor will not be suitable for a low-power one, and vice versa.
Can I use a relay from another brand?
Often it is possible if the technical characteristics match: compressor power (in watts or HP), connection type (number of contacts) and mounting geometry. However, it is better to look for an original analogue or a proven substitute.
Step-by-step diagnostic instructions
Before buying a new part, you need to make sure that the problem is in the relay, and not in the compressor or wiring. To carry out diagnostics, you will need a multimeter (tester) and a minimum set of tools. Safety first: before starting any work, the refrigerator must be disconnected from the electrical network!
Remove the back cover at the bottom of the refrigerator to gain access to the compressor. The relay is usually placed on the side or bottom fitting of the compressor and covered with a plastic casing. Carefully remove the casing and disconnect the wires. Now you can begin visual and instrumental inspection.
☑️ Checking the relay with a multimeter
The first stage is visual and tactile. Pick up the relay and shake it. If a clear ringing or knocking sound of parts coming off is heard inside, the device is definitely faulty. Next, inspect the contacts: they should not be blackened, melted or oxidized. The presence of carbon deposits indicates poor contact and sparking during operation.
The second stage is testing with a multimeter. Switch the device to resistance measurement mode (Ohm).
1. Checking the posistor: measure the resistance between the contacts to which the starting winding is connected. It should be within normal limits (usually several tens of ohms, depending on the model). If the resistance is infinitely high or equal to zero, the posistor is faulty.
2. Checking thermal protection: test the circuit going to the working winding. The resistance should be close to zero (short circuit). If the circuit does not ring, it means that the bimetallic strip has burned out or lost contact.
⚠️ Attention: Do not try to test a relay that is energized. All resistance measurements are carried out only with the device completely de-energized and disconnected from the wires. Failure to follow this rule may result in electric shock and failure of the multimeter.
If there are no visual defects and the tester shows normal values, but the refrigerator does not work, the problem may be deeper. Perhaps the relay “breaks through” only under load or when heated. In such cases, it is recommended to replace it with a known-good device, since the cost of the relay is low, and the risk of burning the compressor is high.
Replacing the starting relay with your own hands
If diagnostics have confirmed a malfunction, you can make the replacement yourself. This is one of the simplest operations in refrigerator repair, not requiring soldering or special equipment. The main thing is to buy the right spare part. The model number is usually indicated on the body of the old relay or in the technical documentation of the refrigerator.
The replacement process takes no more than 15-20 minutes. First, remove the old device by carefully disconnecting the terminals. Make a note or take a photo of which wire was connected where. Clean the contacts on the compressor from possible oxide if they are dirty. The new relay is put on the compressor contacts until a characteristic click is heard.
Connect the wires according to the diagram. They are usually color-coded or labeled (S—starter, R—operational, C—general). Make sure the connections are tight and not loose. If the terminals are oxidized, it is better to clean them or replace them. After assembly, install the protective cover and secure it.
After installation is complete, plug in the refrigerator. You should hear the compressor start confidently without a long hum. After a few minutes, check whether the condenser (grid at the back) begins to heat up - this is a sign that the refrigerant has circulated and the system is working correctly.
Causes of frequent breakdowns and prevention
Why do relays fail? The main enemy of electronics and electricians is power surges in the network. Sudden changes can lead to breakdown of the posistor or burning of contacts. To protect expensive equipment, it is recommended to use voltage stabilizers or at least good quality surge protectors.
Another reason is compressor overheating. If the refrigerator is standing close to the wall, the ventilation is poor, and the motor is working with increased load. The thermal relay operates more often, the bimetallic plate gets tired and loses its properties. Frequent switching on and off is also harmful: if you just turned off the refrigerator, wait 5-10 minutes before starting it again so that the pressure in the system has time to equalize.
- 🧹 Cleanliness: Regularly vacuum the condenser at the back of the refrigerator. Dust acts as a heat insulator, interfering with cooling.
- ⚖️ Smooth installation: Make sure the refrigerator is level. Misalignment can disrupt the operation of the oil in the compressor and the mechanics of the relay.
- 🔌 Network quality: Monitor the condition of the socket. Poor contact in the socket causes sparking and heating of the plug, which affects the entire power circuit.
Timely replacement of door seals also indirectly affects the life of the relay. If the door does not close tightly, the compressor is forced to work almost without stopping, which shortens the service life of all its components, including the starting group.
Can the relay be repaired?
Theoretically, the induction relay can be disassembled and the contacts can be cleaned with fine sandpaper or a burnt-out coil can be replaced. However, given the low cost of a new spare part and the labor intensity of the process, repairing old relays is not economically feasible.
How can you understand that it is the compressor that has burned out, and not the relay?
If, after replacing a working relay, the compressor still does not start (hums or is silent), and at the same time, testing the windings with a multimeter shows a break (infinite resistance) or short circuit (resistance is close to zero between the windings or to the housing), which means the motor itself is faulty. Also, a sign of the death of the compressor may be the absence of the characteristic sound of “suction” with a finger to the fitting when turned on.
Where can I find the relay markings?
The marking is usually applied to the plastic body of the relay itself. Look for the manufacturer's logo (Danfoss, Ranco, Siemens, etc.) and model code (for example, 112N0011, PTCR, etc.). Also, information may be on a sticker inside the refrigerator compartment or in the technical data sheet of the device.
Is it dangerous to change the relay yourself?
Replacing the relay itself is safe, since it does not affect the refrigerant (freon) circulation system. The only danger is electric current, so the main rule is to completely unplug the device from the outlet before starting work. If you are not confident in your abilities, it is better to call a specialist.
How much does a starting relay cost?
The cost depends on the type and manufacturer. Simple posistor relays are inexpensive (from 500 to 1500 rubles). Combined or rare models may cost more (up to 3,000 rubles). Original spare parts are always more expensive than universal analogues.