A sudden stop of the compressor or its inability to start often indicates a malfunction of the start protection relay. In Soviet and Russian refrigerators, such as Atlant, Biryusa or Saratov, the most common devices are the RTK series. It is this small black box that is responsible for supplying voltage to the motor windings and protecting against overloads. If the refrigerator hums but does not turn on, or the compressor only works for a few seconds, the problem most likely lies in this unit.
Checking the RTK relay is a procedure that you can perform yourself, having at hand basic set of tools Start relay is a mechanical switch that operates at a certain current, closing the starting winding. Over time, the contacts can burn and the thermoplastic washer can become deformed, leading to failure of the entire cooling system. In this article, we will look at how to accurately diagnose a malfunction and understand whether a part needs to be replaced.
The operating principle and design of the RTK relay
The RTK series device is a current starting relay with thermal protection. Inside the plastic case there are two main functional parts: the trigger mechanism and the bimetallic strip. When you turn on the refrigerator, current passes through the coil winding, creating a magnetic field. This field draws in the core, which closes the contacts of the starting winding of the electric motor.
After the rotor starts, the current in the circuit drops, the magnetic field weakens, and the contacts open under the influence of gravity or a spring. Thermal protection operates in parallel with this process. If the current exceeds the norm (for example, when the piston group is jammed), the bimetallic plate heats up and opens the circuit, preventing the motor from burning out. Thermal relay in this circuit it plays the role of a fuse that saves an expensive compressor from overheating.
Design RTK-X, where "X" often indicates a modification or manufacturer (for example, Cold), assumes vertical installation on the side fitting of the compressor. It is important to understand that there are no electronics inside, only mechanics and metal. This makes the device quite reliable, but susceptible to physical wear of the contacts and deformation of the plates during frequent power surges.
What is the difference between RTK and RTP?
RTK relays are current-operated, they are triggered by the current flowing through the winding. RTP relays are positional, their movable core moves depending on the position of the relay itself (vertically or horizontally). They are not interchangeable without modifications, since they have different operating principles and contact designs.
External signs of a starter malfunction
Before disassembling the refrigerator and getting tools, you should pay attention to the characteristic symptoms that a faulty relay produces. Often the breakdown manifests itself in the cyclical behavior of the unit: the motor tries to start, makes a click, hums for a few seconds and turns off again. This cycle can be repeated endlessly until you unplug the device.
Another obvious sign is the characteristic smell of burning or melted plastic in the compressor area. If the relay sparked for a long time or the contacts were stuck in the closed state, the plastic case could melt. In this case, a visual inspection will immediately show blackening, traces of soot, or deformation of the device body.
⚠️ Attention: If, after clicking the relay, the compressor continues to hum quietly for more than 5-10 seconds, immediately turn off the refrigerator! Prolonged supply of voltage to a blocked rotor or faulty starting winding will lead to an interturn short circuit and complete combustion of the engine.
It is also worth listening to the sound of operation. A working relay makes a clear, single click when starting up. If you hear a rattling sound, a series of rapid clicks, or a humming sound that ends abruptly, this is a sure sign that contact group needs attention. Sometimes the relay may simply not click at all, which indicates an open circuit inside the coil or a thermal release.
Preparation for diagnostics and safety precautions
Any work with electrical equipment requires strict adherence to the rules security. The first and most important step is to completely disconnect the refrigerator from the electrical network. It is not enough to simply turn off the button on the thermostat - you need to unplug the plug from the socket. The residual voltage in the capacitors (if they are in the circuit) must have time to discharge, so it is recommended to wait 2-3 minutes before starting work.
To check, you will need a minimum set of tools: a screwdriver for removing the compressor protective casing, pliers and, most importantly, a multimeter (tester). Without a measuring device, diagnostics will be only approximate (“at random”), which can lead to the purchase of unnecessary spare parts. Also have a clean rag and possibly some contact spray ready to clean oxidized surfaces.
Get to the compressor, which is usually located at the lower rear of the unit. Remove the metal or plastic cover covering the motor-compressor. You will see a black cylindrical tank with matching tubes and a black plastic box attached to the side - this is our relay. Carefully remove the retaining bracket or strip holding the relay to the fitting and disconnect it.
☑️ Safety precautions during repair
Visual inspection and mechanical check
After removal conduct a thorough external inspection of the RTK-X relay from the seat. Shake the device near your ear: there should be no rattling or sound of parts falling off inside. If you hear the metal core knocking against the walls of the case, it means that the mechanism is damaged and requires replacement. The integrity of the housing is also critical: cracks can lead to moisture ingress and a short circuit.
Inspect the contact groups. To do this, you may need to carefully open the relay case, if its design allows this (it is often assembled with latches or screws). Inside you will see copper contacts and a moving core. They should not have soot, oxides or traces of melting. Contact they should be clean and shiny; black deposits indicate a poor connection and sparking.
Check the condition of the bimetallic plate of the thermal release. It should be smooth, without signs of severe overheating (blue or blackening). If the plate is bent or deformed, the thermal protection will not operate correctly - either too early or not at all, which is dangerous for the motor. Also check the integrity of the inductor: it should not have any broken turns.
Electrical test with a multimeter
The most accurate result is obtained by checking the electrical parameters with a multimeter. Switch the device to resistance measurement mode (Ohms). First check the integrity of the start relay coil. Apply the probes to the corresponding coil contacts: the device should show low resistance (usually from 3 to 10 ohms, depending on the model). If the screen shows “1” or “OL” (infinity), then there is a break in the coil and the relay is faulty.
Then check the thermal relay. When cold, its contacts should be closed. The resistance between the input and output of the thermal release should be close to zero (0.1–0.5 Ohm). If the multimeter shows a break, it means that the thermal protection has already tripped and has not been restored, or the plate is permanently deformed. You can gently press the plate (if you have access) to hear an opening click, but in operating condition it is closed.
Pay special attention to checking for short circuits. Ring contacts that should not be connected to each other (for example, input and housing, or different phases). Here the multimeter should show infinity. Any resistance at these points indicates an insulation breakdown, which makes the use of the relay dangerous.
| Validation parameter | Normal value | Malfunction |
| :--- | :--- | :--- |
| Coil Resistance | 3-10 ohms | Open (∞) or short circuit (0 Ohm) |
| Thermal relay contacts