How to connect a refrigerator thermal relay: complete replacement instructions

The sudden stop of operation of a refrigeration unit often takes you by surprise, but in many cases the cause of the breakdown is the failure of the start-up protection device. Thermal relay is a compact but critical element that protects the compressor motor from overload and overheating. If you notice that the motor hums but does not start, or it turns on and off immediately with a characteristic click, most likely the problem lies in this unit.

Independent replacement of this component requires a minimum set of tools and basic knowledge about the design of electrical circuits. However, before taking active steps, it is necessary to clearly understand the principle of operation of the mechanism and observe all precautions. In this article, we will analyze in detail how to correctly diagnose a malfunction, choose a suitable analogue and make a competent connection without calling a technician.

It is worth noting right away that working with the electrical components of the refrigerator implies the presence of a voltage in the network of 220 volts. Careless handling of the wiring can lead to a short circuit or electric shock. Therefore, the first and most important rule is to completely de-energize the equipment before starting any manipulations. Let's look at the stages of work sequentially to eliminate the risk of damage to the compressor.

The operating principle and design of the start-up relay

To successfully make the connection, you need to understand exactly how this unit functions. Structurally, the device is a housing, inside of which there are two main elements: a starting coil and a bimetallic plate. Bimetallic plate responsible for thermal protection: when a current higher than the nominal current passes through the motor windings, it heats up, bends and opens the contacts, stopping the motor.

The starting part of the mechanism is responsible for supplying voltage to the starting winding of the engine at the moment of start. As soon as the rotor reaches the required speed, the current drops and the relay turns off the starting winding, leaving only the main winding to work. Modern models often use posistor relays, where the role of a switch is played by a thermistor that changes its resistance when heated.

⚠️ Attention: Using a relay with unsuitable operating current characteristics can lead to burnout of the compressor windings or constant false shutdowns.

There are several types of devices, and their interchangeability is not always obvious. Some models are universal, others are tailored for specific brands, such as Indesit, Atlant or LG. It is important to pay attention to the position of the contacts and the method of attachment to the compressor housing, since the geometry of the housing may differ.

What is the difference between a posistor relay and an electromagnetic one?

A posistor relay does not have moving contacts and operates silently, changing resistance when heated by current. Electromagnetic uses a coil and core to open the circuit, which is accompanied by a characteristic click.

Fault diagnosis before replacement

Before ordering a new part, you should make sure that the problem is really in the relay. Often the symptoms of a compressor and starter failure are similar. Primary diagnosis is carried out visually and auditorily. If, when you turn on the refrigerator, you hear a loud click, followed by a hum, and after a few seconds the motor goes silent and clicks again, this is a classic sign of a malfunction of the starting group.

Remove the back cover of the refrigerator and get to the compressor. Carefully remove the plastic casing covering the relay and starting capacitor (if equipped). Remove the device from its seat. Visual inspection may reveal obvious signs of overheating: blackening of the plastic, melting of contacts or the presence of carbon deposits.

• 🔍 Shake the relay near your ear: if you hear a rattling sound, it means the inside has broken off core or contacts that require replacement.
• 🔌 Check the contacts with an ohmmeter: when cold, the resistance between certain terminals should be zero (closed), and when heated (or turned over for some models) it should open.
• 🌡️ Assess the condition of the bimetallic plate: it should not have cracks or severe deformation.

If there is no external damage, but the refrigerator does not start, it is recommended to check with a multimeter. Ring the circuit between the contacts. For electromagnetic relays, the coil resistance is usually several tens of ohms. If the device shows infinity or zero where it should not be, the part is faulty.

Selection of an analogue and labeling of devices

Choosing the right spare part is half the success of the repair. The body of the old relay is always marked, which contains information about the manufacturer, type and electrical parameters. You need to look for a replacement first of all using this code. However, if the original part cannot be found, you can select an analogue based on the technical characteristics.

The key parameter is rated current the operation of the thermal release. It must match the specifications of your compressor. If you install a relay with a lower current, the refrigerator will constantly turn off. If it is large, the protection will not work in case of overload, which threatens to burn out the engine.

It is also important to consider the type of compressor (low-speed or high-speed) and installation position (vertical or horizontal). Some relays only work in a certain position relative to the ground due to the characteristics of the gravitational shutdown mechanism.

When purchasing universal kits, carefully read the instructions inside the package. They are often supplied with a set of adapters and pins, which allows one relay to be adapted to many different compressor connectors. The main thing is to correctly compare the conclusions.

Preparation for replacement and safety measures

The replacement process begins with preparing the workplace and tools. You will need Phillips and flat-head screwdrivers, side cutters (nippers), electrical tape or heat shrink, and a multimeter for the final check. Do not forget to prepare a container for draining condensate if it has accumulated in the compressor niche.

The most important rule: before starting work, be sure to disconnect the refrigerator from the electrical network. Don't just remove the plug from the socket, but also make sure that there are no other voltage sources in the access area. The capacitor, if present in the circuit, can retain a charge, so its contacts should be carefully discharged by shorting it with a screwdriver with an insulated handle.

Ensure good lighting of the work area. The compressor area is often dusty, so it is recommended to first vacuum or wipe the surface around the motor to prevent small debris from getting inside the electrical contacts during disassembly.

⚠️ Attention: Never try to remove the relay from the compressor contacts while it is hot. Allow the unit to cool for 30-40 minutes after the last start to avoid damaging the plastic elements and causing burns.

Step-by-step instructions for connecting a relay

Now let's move directly to the process of dismantling the old part and installing a new one. Remove the retaining bracket or bar that holds the relay to the compressor housing. It is usually secured with two screws or snapped into place. Gently pull the relay down, removing it from the three pins of the compressor.

Pay attention to the wiring diagram. In older models, the wires may go directly to the relay terminals. In modern ones, they are inserted into connectors on the device body itself. Take a photo location of wires before disconnecting them. This will help avoid errors during assembly.

If your new relay has a different type of connector, you may have to transfer the contacts from the old housing. To do this, carefully cut the wires at the base of the old relay (leaving some extra length) or disconnect the terminals. Strip the ends of the wires by 5-7 mm, if necessary.

Connection diagram (standard):
Pin 1 (S) -> Start winding
Pin 2 (R) -> Working winding
Contact 3 (C) -> Common (phase)

Connect the wires to the new relay according to the diagram. If using a universal relay with an adapter set, choose one that fits snugly over your compressor pins. Make sure the contacts are tight and not loose. Push the relay onto the compressor pins as far as it will go.

• 🔌 Make sure that the markings on the relay correspond to the markings on the compressor terminals (S, R, C).
• 🛡️ Check whether the relay body does not overlap any other elements or tubes.
• 🔩 Securely fasten the retaining bar so that the vibration of the compressor does not break the relay.

First start-up and performance check

After installing all the elements in place, do not rush to immediately close the back cover. Plug in the refrigerator and listen. The compressor should start after a few seconds (or immediately, depending on the model) with a characteristic hum. A click at startup is acceptable for electromagnetic relays.

Check the heating of the relay housing during operation. After 10-15 minutes of compressor operation, touch the relay (be careful, it may be hot). It should be warm, but not hot. If you hear a crackling sound, sparking, or the relay constantly clicks, immediately unplug the appliance.

Make sure that the refrigerator has begun to get cold. Place your hand on the side wall inside the chamber - it should gradually cool down. If the compressor runs continuously for more than 40 minutes and there is no cold, perhaps the problem is not only in the relay, but also in a freon leak or a malfunction of the motor itself.

⚠️ Attention: If after replacing the relay the compressor hums, but does not start, and after a few seconds a shutdown click is heard, the compressor itself may be jammed. Attempts to turn it on frequently can permanently damage it.

Frequent installation errors and their consequences

Even with instructions, beginners often make mistakes, which ruin all your efforts. One of the most common is ignoring the polarity or mixing up the contacts of the starting and working windings. This may cause the motor to hum, rotate in the opposite direction (if possible), or immediately go into protection.

Another error is poor contact at the junction of the wires. If you used twist instead of soldering or a high-quality terminal, over time the contact point will oxidize and begin to heat up. This creates a risk of insulation fire and repeated breakdown of the equipment.

Also, you should not install a relay designed for a different type of refrigerant or compressor power, “just to fit it in size.” A difference in operating currents of even 0.5 Amperes can be critical for the durability of the motor.

If you are faced with a situation where a new relay burns out immediately after installation, do not continue the experiments. This is a sure sign that there is a short circuit in the circuit or that the compressor itself is faulty (turn-to-turn short circuit of the windings). Further operation without professional diagnostics is dangerous.

Is it possible to temporarily start a refrigerator without a relay?

Theoretically, you can apply voltage directly, but this is extremely dangerous. The compressor can burn out in a matter of seconds if it jams, and there is also a high risk of electric shock. This can only be done for short-term diagnostics by a technician.

Questions and answers (FAQ)

Is it possible to repair an old thermal relay, or just replace it?

In most cases, repairs are unprofitable and impossible. The relay body is often soldered or riveted, and the bimetal strip and contacts are strictly calibrated at the factory. An attempt to clean the contacts or bend the plate will disrupt the accuracy of the protection, which can lead to the burning of an expensive compressor. Only a complete replacement is recommended.

Why does the new relay click, but the refrigerator does not turn on?

If you hear the relay click, but the compressor does not start (does not hum), the engine starting winding may be faulty or the relay itself is not supplying voltage to the starting circuit. If the compressor hums, clicks and turns off, the relay may be selected incorrectly (the response current is too low) or the compressor is mechanically jammed.

Is a universal relay suitable for my refrigerator?

Universal relays (for example, 100N, 101N series) are suitable for most household refrigerators power up to 300-400 W. However, it is important to check the diameter of the pins and their location. Universal relays often come with adapter frames and additional contacts for adaptation to different models.

How often do you need to change a thermal relay?

The service life of a high-quality relay is 10-15 years or more. It does not require scheduled replacement. It is replaced only when it fails. Frequent relay burnouts (once a year or more often) indicate problems with the power supply (voltage surges) or a malfunction of the compressor itself, which consumes increased current.