When a household refrigerator breaks down, one of the most common diagnoses is the failure of the start-up relay. This small device is responsible for starting the compressor motor and protecting it from overloads. When the refrigerator stops freezing, and the compressor either hums but does not start, or clicks and immediately turns off, experienced technicians check this particular unit first.
However, when trying to find a replacement in stores or spare parts markets, the owner often encounters confusion in the markings. There may be RKT-1, RKT-2, RTK-1, RTK-2, RTK-3 many other modifications on the shelves. They may look similar visually, but the internal design and electrical characteristics are different. An incorrectly selected part can lead to repeated breakdown or even burning of the motor windings.
In this article we will analyze in detail the design features of various relay series, explain the logic of their numbering and help you determine which analogue is suitable for your case. Understanding the principle of operation starting winding and protective mechanism will allow you not only to replace the part, but also to understand the reason for its failure.
Principle of operation and design of the starting protection relay
To understand the difference between the models, it is necessary to briefly consider their internal structure. A classic electromagnetic relay consists of two main functional blocks: starting and protective. The starting part usually contains a coil, which, when voltage is applied, creates a magnetic field that closes the contacts of the compressor starting winding. As soon as the motor rotor picks up speed, the current drops and the contacts open.
The protective part is a bimetallic plate, which is heated by the current passing through the main winding. If the current exceeds the norm (for example, when the piston group is jammed or the network is overloaded), the plate bends and opens the circuit, preventing engine combustion. It is on the quality and calibration of this bimetallic plate reliability of the protection depends.
⚠️ Attention: Installing a relay with a protection response current exceeding the rated current of your compressor can lead to irreversible damage to the engine if overloaded. Always check the markings of the current characteristics.
The differences between the series RKT and RTK often lie precisely in the design of the trigger mechanism and the method of attachment to the compressor housing. Some models use rigid mounts, others use flexible leads. The location of the contacts also varies: in some relays they are located on the top, in others - on the side, which affects the possibility of installation in a specific refrigeration unit.
Decoding of abbreviations and nomenclature
The marking of domestic relays, which were massively installed in refrigerators of Soviet and post-Soviet production (such as Atlant, Biryusa, Zil, Don), was built according to a certain logic. The abbreviation RKT stands for “Coil Thermal Relay”. The number at the end indicates a series or modification developed for certain types of compressors.
There is also a series RTK (Thermal Coil Relay), which is often confused with RKT. The main difference lies in the type of trigger coil used and the current characteristics. For example, RTK-1 is intended for single-phase motors with increased starting torque, while RTK-2 and RTK-3 have other response parameters. An error of one character can cost the performance of the equipment.
It is important to consider that manufacturers could change the design within the same series. Therefore, when selecting an analogue, it is not enough to know only the name of the series. It is necessary to pay attention to:
- 🔌 Location and number of connection pins (2, 3 or 4 contacts).
- ⬇️ Installation orientation (contacts down or up), since some relays use the gravitational opening principle.
- 📏 Overall dimensions, especially the height of the case so that the part fits in the compressor niche.
Modern analogues may have a body shape different from the original, but retain identical electrical parameters. The main thing is that operation current i type of trigger mechanism meet the requirements of your refrigerator engine.
Comparative analysis of RKT and RTK models
Models with numbers 1, 2 and 3 appear most often in queries. Let's look at their key differences. Models of the series RTK-1 and RTK-2 are often interchangeable within the same line of compressors, but have different protection shutdown thresholds. RTK-3 usually designed for more powerful engines or have a modified coil design.
Series RKT often found in older models of refrigerators. Their main feature is the specific shape of the coil and the method of attachment to the frame. When replacing RKT-1 to RKT-2 it may be necessary to modify the seat or use an adapter frame, since the geometry of the fasteners is different.
Below is a table that helps systematize the main differences between popular models:
| Relay model | Trigger type | Approximate protection current (A) | Compatibility |
|---|---|---|---|
| RTK-1 | Electromagnetic | 1.3 - 1.6 | Low power compressors |
| RTK-2 | Electromagnetic | 1.8 - 2.2 | Average power, often analogous to RTK-1 |
| RTK-3 | Electromagnetic | 2.5 - 3.0 | More powerful engines |
| RKT-1 | Reel (old type) | Depends on modification | Old models of refrigerators |
It is worth noting that the data in the table are averaged. Actual parameters may vary depending on the year of manufacture and manufacturer. Therefore, when purchasing, always check rated currentindicated on the body of the old part.
Is it possible to install a relay with a high operating current?
Theoretically, the engine will start, but the protection will not operate in time when overload. This will lead to overheating and burning of the compressor windings. It is also impossible to install a relay with a lower current - the refrigerator will constantly turn off before it can start.
Installation nuances and interchangeability
When replacing a relay, it is important to take into account not only the electrical parameters, but also physical compatibility. It often happens that electrically RTK-2 it completely fits the compressor on which it was installed RTK-1, but the holes for the mounting screws do not match. In such cases, craftsmen use universal adapter frames or carefully resolder the contacts if the design allows.
Particular attention should be paid to the orientation of the relay during installation. Most electromagnetic starting relays (series RTK, RKT) are gravitational. This means that the moving contact closes and opens under the influence of gravity and magnetic field. If you install such a relay upside down or on its side (if this is not provided for by the design), it simply will not work.
☑️ Check before installation
⚠️ Attention: Before installing a new relay, be sure to inspect the contact pads on the compressor itself. If they are blackened or oxidized, they must be cleaned, otherwise the new relay will quickly fail due to poor contact.
In some cases, it is possible to replace domestic relays with foreign analogues (for example, Danfoss or Secop). For this purpose, special adapters are used, which come complete with universal relays. Such a replacement is often even more reliable, since modern components have better characteristics.
Diagnostics of relay faults
How to understand that the problem is in the relay and not in the compressor? There are several simple signs. If, when you turn on the refrigerator, you hear a characteristic click, followed by a hum that lasts 3-5 seconds, and then a click again (after which the hum stops) - this is a classic symptom of a faulty starter or a jammed compressor.
A visual inspection can also provide a lot of information. If you see traces of burning, melted plastic, or smell burnt insulation inside the relay housing, the part definitely needs to be replaced. It is also worth checking the starting coil for a break - for this you can use a multimeter in continuity mode.
Checking algorithm:
- 🔍 Remove the relay and shake it: if you hear a knocking sound from the internal parts, the core or contacts may be damaged.
- 📟 Test the circuit with a multimeter: there should be resistance between the contacts (for a coil) or a short circuit (for a bimetallic plate in a cold state).
- 🌡️ Check the thermal release: heat the bimetallic plate (carefully!), it should open.
It is important to distinguish between a breakdown of the relay itself and compressor malfunction. If, after replacing the relay with a known good one, the situation does not change (the clicks continue, there is no start), there is a high probability of an interturn short circuit in the motor windings or mechanical jamming of the piston group.
Frequent errors during selection and replacement
One of the most common mistakes is ignoring the type of refrigerant and compressor power when choosing a relay. Although the relay controls electricity, the performance of the engine directly depends on what kind of freon it runs on and what its performance is. An attempt to save money and install “any similar” relay often leads to a second visit to the spare parts store a week later.
Another mistake is a violation of the sequence of connecting the wires. In three-pin circuits, mixing up the phase, neutral and start windings can lead to a short circuit. Always take a photo of the connection before removing the old relay or use markings on the wires.
Keep in mind that specifications and parts availability are subject to change. Refrigerator manufacturers can update their model range by changing component suppliers.
⚠️ Attention: Relay compatibility information may be updated by manufacturers. Before purchasing expensive universal kits, check the current correspondence tables on the spare parts manufacturer’s website or consult with official dealers.
A competent approach to diagnosing and replacing the start-up relay allows you to restore the operation of the refrigerator at minimal cost. The main thing is attention to the details of marking and compliance with electrical safety rules.
Is it possible to install an RTK-2 relay instead of an RTK-1?
In most cases, this is possible, since they belong to the same series and have similar characteristics. However, it is necessary to check the tripping current of the thermal release. If the RTK-2 current is higher, the protection will be less sensitive, which is risky. If lower, false shutdowns are possible.
Why does a new relay burn out after a few days?
There may be several reasons: incorrect orientation during installation, mismatch in operating current, poor contact at the compressor terminals, or, worst of all, a malfunction of the compressor itself (turn-to-turn short circuit), which “kills” serviceable ones relay.
What is the difference between a relay for a single-compressor and a two-compressor refrigerator?
In principle - nothing if the power of the compressors is the same. In two-compressor refrigerators (for example, Atlant) there are usually two identical relays, one for each motor. The main thing is the power of a particular compressor, and not the number of chambers.