A sudden stop in the operation of a refrigeration unit often takes people by surprise, causing panic about food spoilage and the need for expensive repairs. When independently diagnosing malfunctions, owners of household appliances often come across an abbreviation RKTprinted on a small plastic or carbolite block attached to the compressor. Understanding what exactly is hidden behind these letters is the first step to restoring the functionality of your equipment without calling a repairman.
This component is a start-up relay that plays a critical role in starting the compressor motor. If the refrigerator hums but does not start, or, conversely, turns on and off immediately with a characteristic click, the problem most likely lies in this unit. In this article we will analyze in detail the purpose of the marking, the principle of operation and methods for restoring the functionality of the device.
Deciphering the abbreviation RKT
The marking on the device body is not just a set of random symbols, but a standardized designation adopted in Soviet and post-Soviet technical documentation. The abbreviation RKT is deciphered as follows: “P” means relay, “K” means compressor, and “T” means thermal. Thus, we have before us a combined device that combines two independent functions of protection and starting.
The main task of this element is to briefly connect the starting winding of the electric motor at the time of start, as well as to turn off the power when overcurrent occurs. Thermal protection triggered if the current in the circuit exceeds permissible standards, preventing overheating of the motor windings and possible fire. Without a working RKT relay, normal operation of a single-phase asynchronous refrigerator motor is impossible.
It is worth noting that there are various modifications of these devices, which may have additional indices indicating specific characteristics or design features. For example, there are models RKT-1, RKT-2, RKT-3 and so on. The number at the end of the marking usually indicates the operating current or overall dimensions, which is important to consider when selecting an analogue for replacement.
It is critically important to understand that RKT relays are designed strictly to operate with alternating current of a certain frequency (usually 50 Hz) and voltage (220-230 V), and their installation in a circuit with other parameters is unacceptable. Violation of these conditions can lead to instant failure of not only the relay itself, but also an expensive compressor.
Operation principle and internal structure
Inside the RKT relay case two main elements are hidden: a starting relay and thermal protection relay. The starting device is most often made according to an induction circuit and contains a movable core, which, under the influence of a magnetic field, is drawn into the coil when voltage is applied. This movement closes the contacts, supplying power to the compressor starting winding, which creates the necessary torque.
Once the motor rotor reaches sufficient speed (usually about 75% of the rated speed), the current in the circuit drops, and the core, under the influence of gravity or a spring, returns to its original position, opening the contacts of the starting winding. The motor then continues to operate on the main winding. Thermal protection is a bimetallic plate that bends when heated, opening the power circuit when overloaded.
The design of the device may vary depending on the manufacturer and year of manufacture. Early models often had a black carbolite body, while modern counterparts may be made of heat-resistant plastic. Contacts made of silver or other alloys that are resistant to the formation of a spark arc may also be located inside.
⚠️ Attention: The internal structure of the RKT relay is not sealed. The ingress of moisture, condensation or aggressive cleaning agents into the housing can lead to oxidation of the contacts and incorrect operation of the protection, which is dangerous for the electric motor.
For clarity, let's look at the main components that make up a typical relay of this series:
- 🔌 Case: Dielectric shell that protects internal elements from dust and mechanical damage.
- ⚙️ Electromagnetic coil: Creates a magnetic field to retract the core during startup.
- 🔥 Bimetallic plate: The main thermal protection element that responds to heating.
- 🤝 Contact group: Moving and fixed contacts for switching circuits.
Why does the relay click?
If you hear frequent clicks, this means that the thermal protection is cyclically turned on and off. This happens because the bimetallic strip heats up from the increased current, opens the circuit, cools down and closes again. This mode of operation indicates a malfunction of the compressor (interturn short circuit) or the relay itself.
Typical symptoms of a relay malfunction
Diagnostics of the state of the start-up protection device does not always require sophisticated equipment. Often the nature of the refrigerator itself suggests where the problem lies. If you notice that the motor hums for a few seconds, then there is a click and there is silence, this is a classic sign that the starting winding is not connected or the protection current is triggered instantly.
Another common symptom is the situation when the compressor does not respond at all when turned on, although the light in the refrigerator is on. This may indicate an open circuit in the thermal relay or a complete lack of contact in the starting group. It is also worth paying attention to the appearance of the relay itself: blackening, melting of the plastic or a burning smell are clear signals that replacement is necessary.
Sometimes the refrigerator may operate unstably, turning on and off at short intervals without visible load. This phenomenon is called "clocking" and is often caused by sticking contacts or improper operation of the bimetal strip. In such cases, the relay may pass current, but not provide a reliable connection.
There are a number of signs by which you can preliminary assess the condition of the unit:
- 🔊 Characteristic click: Sounds 3-5 seconds after switching on and repeats cyclically.
- 🌡️ Heating of the housing: Excessive heating of the relay itself or the wires going to it.
- 💥 Knockout of plugs: Short-term short circuit when trying to start.
- 👃 Ozone smell: Indicates an insulation breakdown or a strong sparking arc inside the contacts.
Instructions for dismantling and inspection
Before starting any work, you must strictly follow the electrical safety rules. Be sure to disconnect the refrigerator from the electrical networkby unplugging the cord from the socket. Only after this can you remove the back panel at the bottom of the unit to gain access to the compressor and the relay attached to it.
Removing the relay is usually not difficult: it is fixed on the terminals of the compressor and can additionally be secured with a bracket or clamp. Carefully remove the retaining bracket and pull the relay down, disconnecting it from the motor contact group. Be careful not to pull sharply, so as not to damage the suitable wires.
For an initial check, you can use the “shaking” method. Take the relay in your hand and shake it near your ear. If you hear a bell-like noise inside, this means that the core has become detached from the damper or has collapsed. In this case, the relay must be unconditionally replaced, since it is impossible to restore its mechanical integrity.
☑️ Procedure for dismantling
More accurate diagnostics can be carried out using a multimeter in resistance measurement mode. Ring the contacts of the thermal relay - they should “ring” (have low resistance). The resistance of the start relay coil should also be low. If the device shows infinity (open) or zero (short circuit) where it should not be, the part is faulty.
Correspondence table and compatibility of analogues
When searching for a replacement, the issue of compatibility often arises. RKT relays have many modifications, and it is important to select a device with similar operating current characteristics. Using a relay with a cut-off current that is too low will lead to constant false alarms, and with a cut-off current that is too high, the compressor windings will burn out.
Below is a table that helps you navigate the main parameters of various modifications of the RKT series. Please note that these parameters may vary slightly depending on the manufacturer.
| Relay model | Rated current (A) | Trigger current (A) | Contact type | Compatibility |
|---|---|---|---|---|
| RKT-1 | 1.4 | 2.2 | Normally open | Low-power compressors |
| RKT-2 | 1.8 | 2.7 | Normal open | Average power |
| RKT-3 | 2.5 | 3.5 | Normally open | Powerful units |
| RKT-6 | 1.0 | 1.6 | Normally open | Low power |
It is important to consider that modern refrigerators often use relays of other series, for example RT, RTP, RSO or electronic starting devices. Direct replacement of the RKT with a relay of another series is possible only if the electrical parameters and mounting dimensions are completely identical.
Replacing the relay and installation features
The process of installing a new RKT relay is technically simple, but requires care. The main rule is the orientation of the device in space. There is always an arrow on the relay body indicating the direction “UP” (top) or marking “TOP”. The device must be installed exactly in the position in which it was originally operated, usually with the coil up.
Improper installation (for example, upside down or on its side) will result in gravity being unable to return the core to its original position after starting, and the starting winding will remain on. This will cause rapid overheating and burnout of the compressor starting winding. Therefore, before removing the old relay, it is recommended to take a photo or sketch its position.
After installing the relay on the compressor terminals, you must securely fix it with a bracket and connect the wires according to the previously made diagram or photograph. Make sure that the wires do not touch hot parts of the compressor and have sufficient length for vibration.
⚠️ Attention: Never attempt to solder the thermal relay contacts or jam the start relay core in the operating position. This turns off the motor protection, which, if an overload occurs, will lead to a fire or complete failure of the compressor.
After assembling all the components and installing the protective casing, you can turn on the refrigerator to the network. If the start-up was successful, the motor should start running smoothly, without buzzing or repeated clicks. In the first minutes of operation, it is recommended to periodically check the temperature of the new relay housing - it may warm up slightly, but should not be hot.
Frequently asked questions (FAQ)
Is it possible to replace the RKT relay with a universal one?
Yes, there are universal starting relays that are suitable for a wide range of compressor powers. However, when using them, you must carefully monitor the current range indicated on the packaging and make sure that the power of your compressor falls within this range. It may also be necessary to adapt the seat.
Why does a new relay burn out a short time after replacement?
If a new RKT relay fails soon after installation, this most often indicates a malfunction of the compressor itself. The motor may have an interturn short circuit, which creates an increased starting current, or a mechanical wedge. In this case, the relay performs its protective function, sacrificing itself to prevent a more serious accident.
Where can I find the current marking on the relay?
The marking is usually applied to the side or top edge of the case. Look for numbers next to letters In or just a numerical value (for example, 1.4, 1.8). Also, the parameters can be stamped on a metal plate inside the case if it is collapsible, but it is better to look for them on the outside.
Is it dangerous to change the RKT relay yourself?
Replacing the relay is safe provided that the device is completely disconnected from the network. However, if you are not confident in your abilities, do not have diagnostic tools, or suspect a compressor malfunction, it is better to contact a professional technician. Connection errors can lead to damage to the refrigerator wiring.