A sudden failure of the refrigerator to work, accompanied by a characteristic clicking and humming sound, often indicates problems with the compressor starting mechanism. Start relay is critical a unit that ensures engine starting and normal operation. If you notice that the unit has stopped freezing, and the motor is trying to start, but immediately stalls, most likely this component needs to be replaced.
Replacing the relay yourself is a procedure available to a home craftsman with basic tool handling skills. It allows you to save a significant amount on calling a specialist and purchase a new compressor or a whole refrigerator. The main thing is to strictly follow safety precautions and sequence of actions so as not to damage the motor windings.
In this article we will analyze in detail the design of the protective starting mechanism, methods for diagnosing faults and the step-by-step process of installing a new part. You will learn how to distinguish a burnt out relay from a working one and what nuances to pay attention to during installation.
The operating principle and design of the starting relay
To understand the replacement process, you need to briefly familiarize yourself with the device start-protective relay. This element is an electromagnetic switch that supplies current to the starting winding of the engine only at the moment of starting. As soon as the rotor reaches the required speed, the current in the circuit drops, and the relay opens the contacts, turning off the starting winding.
In parallel with the starting function, the device acts as a thermal fuse. Inside the case there is a bimetallic plate that opens the circuit when the temperature or current increases critically. This protects electric motor from combustion during overloads or jamming.
- 🔌 Contacts: provides voltage to the compressor windings.
- 🔥 Bimetal plate: reacts to heating and opens the circuit when overheated.
- 🧲 Electromagnetic coil: creates a field for closing the starting contacts.
- 🏠 Case: protects internal elements from moisture and mechanical damage.
There are two main types of relays: inductive (old style, often with one contact) and positronic (modern, with three contacts). PTC models are more reliable and do not have moving mechanical parts, relying on the properties of the ceramic element to change resistance when heated. Replacing an induction relay with a posistronic one is possible only if you have the appropriate connection diagram and adapter.
Is it possible to repair an old relay?
Repairing a starting one Do-it-yourself relays are usually impractical. Mechanical jamming of contacts or burnout of a posistor is easier to eliminate by replacing the part. Attempts to clean the contacts often lead to repeated failure after a short time due to a violation of the calibration of the plate.
Fault diagnosis before replacement
Before buying a new part, you need to make sure that the problem lies in the relay, and not in the compressor itself or wiring. Primary diagnosis is carried out visually and auditorily. If, when you turn on the refrigerator, you hear a loud click, followed by a buzzing sound that lasts several seconds, and a second shutdown click, this is a classic symptom of a malfunction of the starting mechanism.
For a more accurate check of the relay, it is necessary to remove it from the compressor. Unplug the refrigerator, remove the rear protective panel and disconnect the connector. Shake the part near your ear: if a ringing or knocking sound is heard inside, it means that the internal elements are destroyed or melted. The whole relay should not make any extraneous sounds when shaken.
⚠️ Attention: If after replacing the relay the situation repeats, and the new element also burns out or does not start the motor, there is a problem may lie in the interturn short circuit of the compressor windings. In this case, the unit itself must be replaced.
You can also check the integrity of the posistor or contacts using a multimeter. The resistance of a working posistor at room temperature should be several tens of ohms. If the device shows infinity or zero, the part is faulty. For induction relays, it is important to check whether the contacts are stuck in the closed state, which will lead to constant voltage on the starting winding and its combustion.
Preparation of tools and selection of a new part
The success of the operation directly depends on the correctness of the selected spare part. Relays are selected strictly for the compressor model, and not for the refrigerator brand. There are always markings on the body of the old relay, for example RKT, PTC, 100N or manufacturer codes like Danfoss, Secop. This data must be rewritten or photographed before going to the store.
To carry out the work you will need a minimum set of tools. It is important that the screwdrivers have insulated handles and that the wire cutters are sharp so as not to damage the wire strands when stripping. Also, do not forget about gloves, since the internal parts of the compressor may be coated with technical oil.
☑️ Tools for replacing relays
If an exact copy of the relay is not found, you can use a universal analogue, but you will need to carefully study the connection diagram. Universal models often come complete with a set of adapters for different types of connectors. Make sure that the current characteristics of the new relay match or exceed those of the old device.
Connection diagram and pinout
The most critical stage is the correct connection of the wires. An error in the connection can lead to a short circuit or failure of the compressor windings. On the body of most relays there is a connection diagram, where the contacts are indicated: S (Start - starting winding), R (Run - working winding) and C (Common - common).
In modern three-pin relays (PTC) contacts are usually arranged in a triangle. The top contact is most often the common one, the bottom left one is the working one, and the right one is the starting one. However, manufacturers may change this configuration, so always check the markings on the case or technical documentation.
| Designation | Function | Wire color (often) | Position on relay |
|---|---|---|---|
| C | Common (phase) | Black / White | Upper or central |
| R | Working winding | Red / Blue | Lower left |
| S | Start winding | Green / Yellow | Bottom right |
| GND | Ground | Green with stripe | Separate screw on the housing |
If you change the type of relay (for example, from inductive to posistronic), the number of contacts may change. In such cases, a special adapter harness or reconnection circuit is used. Induction relays often have one input wire and one output, completing the circuit in series, while positronic ones require connection to the three terminals of the compressor.
Step-by-step instructions for installing the relay
Start work only after completely disconnecting the refrigerator from the power supply. Remove the plug from the socket. Remove the cardboard or plastic cover covering the compressor at the lower rear of the unit. In front of you will be a massive black cylinder - this is the motor-compressor.
Carefully remove the old relay. It can be secured to the compressor terminals simply by a tight fit or held on to a metal retaining bracket. If there is a staple, bend it back with pliers. Disconnect the wires after first remembering or photographing their location. If the wires go directly into the relay body, they may need to be bitten off.
⚠️ Attention: When removing the old relay, be careful not to damage the three copper leads sticking out of the compressor. They are fragile and, if handled carelessly, can break off at the base, which will require expensive repairs with unsoldering the cover.
Install a new relay on the compressor terminals. It should be put on tightly, with slight effort. Orient it so that the inscription UP (if any) faces up, or following the shape of the footprint. Connect the wires according to the diagram: common wire to contact C, working wire to R, starting wire to S. If terminal clamps are used, make sure that they are securely crimped.
Secure the relay with a metal bracket, if provided by the design. Make sure that the wires do not touch hot parts of the compressor and are not stretched. Replace the protective cover and plug in the refrigerator. After 1-2 minutes, a characteristic switch-on click should be heard, and the compressor will start working smoothly, without humming.
What to do if the relay does not stay on the terminals?
Sometimes the seat of the new relay is wider than the old one. In such cases, you can carefully tighten the plastic walls of the connector with pliers or use a layer of heat shrink on the compressor terminals to seal, but only if this does not interfere with contact.
Frequent errors and safety measures
One of the most common mistakes is ignoring the orientation of the relay. Many models, especially positronic ones, are sensitive to position in space. Installation upside down can lead to the posistor not cooling down or, conversely, overheating and the refrigerator will stop starting.
Another error is poor contact in the connections. If you are twisting wires, be sure to use electrical tape or heat shrink. Poor contact causes sparking, heating and may cause a fire. All connections must be mechanically strong and reliably insulated.
- 🚫 Do not turn on refrigerator without an installed protective casing.
- 🚫 Do not use a relay from another type of compressor without checking the circuit.
- 🚫 Do not leave exposed wires inside the case.
It is also important to remember about condensation. If the refrigerator has been in a cold room, allow it to warm up to room temperature for several hours before turning it on. Moisture inside the relay or on the contacts can cause a short circuit at the very first moment of operation.
Is it possible to install a relay from another refrigerator model?
Yes, it is possible if the electrical characteristics (current, voltage) and connection diagram match. The brand of the refrigerator (Indesit, Bosch, LG) is not important, the type of compressor is important (Danfoss, Secop, Embraco). The main thing is that the connector fits or it is possible to transfer the contacts.
Why does a new relay burn out immediately after installation?
This may indicate a malfunction of the compressor itself (jamming, interturn short circuit), problems with the wiring (short circuit in the circuit) or an incorrect choice of relay model (insufficient current load). Also, the cause may be a power surge in the network.
How long does the starting relay last?
The average service life of a high-quality relay is 5-10 years. However, frequent voltage fluctuations in the network, overheating of the compressor due to contamination of the condenser or aging of the refrigerant can significantly reduce this period.
Is it necessary to change the thermocouple along with the relay?
The thermocouple (thermal relay) is often built into the housing of the starting relay or is a separate element. If the thermal protection has tripped due to overheating, it can restore functionality after cooling down. If it is short-circuited or broken, replacement is required along with the trigger mechanism.