A sudden stop in the operation of a refrigeration unit often causes panic, but in many cases the breakdown lies in the failure of a small but critical component - the starting relay. This compact element is responsible for starting the compressor electric motor, providing the necessary impulse to the starting winding. If you notice that the refrigerator hums but does not start, or there is a loud click followed by silence, most likely the problem lies in this unit.
Replacement or connection starting relay is a procedure that can be performed at home if you have basic skills in working with electrical circuits and tools. Understanding the operating principle of this device will help not only restore the functionality of household appliances, but also save significant money on calling a technician. It is only important to observe safety precautions and strictly follow the algorithm of actions, since the work is carried out with electric current and refrigerant.
In this article we will analyze in detail the design of various types of relays, methods for diagnosing them and the step-by-step connection process. You will learn how to distinguish a faulty compressor winding from a burnt-out starting coil, and get comprehensive answers to technical questions. A correctly selected and installed component will ensure stable operation of the refrigerator for many years.
Principle of operation and types of starting relays
The starting relay is an electromechanical switch that closes the circuit of the engine starting winding at the time of start-up and opens it when the rotor reaches a certain speed. Depending on the design and principle of operation, these devices are divided into two main types: induction and posistor. Induction relays, often called "pill" relays, operate by electromagnetic induction and the opening of contacts by gravity or a spring as current increases. PTC models use a temperature-sensitive element that changes its resistance when heated, breaking the circuit.
The key element in induction relay is a movable core, which is drawn into the coil when the starting current is applied, closing the contacts. As soon as the engine reaches operating mode and the current drops, the core drops, opening the starting winding circuit. In posistor devices, the role of a switch is played by a ceramic element with tungsten contacts. When voltage is applied, the posistor heats up, its resistance increases sharply, and the current through the starting winding practically stops.
The choice of the correct type of relay directly depends on the compressor model and its technical characteristics. An incorrectly selected device can lead to overheating of the windings, frequent trips of thermal protection, or complete motor failure. Modern refrigerators, such as Indesit or Atlantare often equipped with posistor models due to their reliability and the absence of moving parts.
For the correct operation of the system, the condition of the windings of the compressor itself is also important. If the starting or operating winding has an interturn short circuit or open circuit, even a working relay will not be able to start the engine. Therefore, before replacing, a primary diagnosis of the electrical circuit is always carried out.
Fault diagnosis before replacement
Before proceeding with the dismantling and installation of a new component, you need to make sure that the problem is in the start relay, and not in the compressor itself or the heat removal system. Primary diagnosis begins with a visual inspection and listening to the operation of the unit. If you hear a characteristic click when turning on, followed by a hum that lasts a few seconds and a second stop click, this is a classic symptom of a faulty starter or a jammed compressor.
The next step is to check the integrity of the motor windings using a multimeter. It is necessary to remove the back cover of the refrigerator, gain access to the compressor and carefully disconnect the terminals. By measuring the resistance between the contacts, you can determine the state of working and the starting windings. The normal resistance of the working winding is usually 10-30 Ohms, and the starting winding is 20-50 Ohms, although the exact values depend on the specific engine model.
⚠️ Attention: If the multimeter shows infinity (open) or resistance close to zero (short circuit) on any of the windings, Replacing the relay will not help. In this case, serious repairs to the compressor or its complete replacement are required, since the internal windings of the motor have burned out.
You should also inspect the relay itself for external damage. The plastic should not be melted, there should be no burning or burning smell inside. If the relay is induction, when shaking near the ear, no rattling of internal parts should be heard, which may indicate destruction of the core. For posistor models, the absence of cracks in the ceramic element is critical.
The thermal protection relay, which is often combined with the starting relay in the same housing or located nearby, also requires checking. It is responsible for turning off the power when the compressor overheats. If the bimetallic strip inside is deformed or the contacts are burnt, the motor will not receive power at all. Checking the integrity of the thermal relay circuit should be done in a cold state.
Hidden signs of compressor malfunction
If, after replacing the relay and checking the electrical system, the compressor still does not start, but at the same time consumes a current higher than the rated one (measured with current clamps), this may indicate a mechanical wedge of the piston group. In this case, an attempt to start multiple times may lead to the final failure of the node. It is recommended to let the unit cool completely for 10-12 hours and try to start it again. If the result is the same, the compressor needs to be replaced.
Tools and preparation for work
To successfully complete the work of replacing the start relay, you will need a minimum set of tools that can be found in the arsenal of most home craftsmen. First of all, you need a multimeter to check the circuits and resistance. You will also need pliers, screwdrivers (Phillips and flathead), side cutters and, possibly, a wire stripper. It would be a good idea to have electrical tape or heat-shrink tubing to insulate connections.
Safety is priority number one. Before starting any manipulations, you must completely disconnect the refrigerator from the power supply. Unplug from the socket and make sure that access to the rear wall of the unit is clear. If the refrigerator is built-in, it will have to be pulled out of the niche, providing access from all sides. Working under voltage is strictly prohibited.
It is important to prepare a workplace with good lighting. The compressor is located at the bottom of the refrigerator, so you may have to sit down or lay the unit on its side (although the latter is not recommended for models with an open oil drain system; it is better to work on a tilt). Prepare a container for small parts in advance so as not to lose screws or terminals.
When purchasing a new relay, be sure to take accurate data from the old device. Marking, number of contacts, type of connection (vertical or horizontal) and motor power - all these parameters must match. Universal relays exist, but they require correct settings or may work less stably than original spare parts for models LG, Bosch or Stinol.
☑️ Preparing to replace the relay
Connection diagram and contact table
The process of connecting the start relay depends on its type and the specific compressor model, but the general logic remains the same. The relay fits onto three contact pins coming out of the compressor housing. These pins form a triangle, and each of them is responsible for a specific function: supplying power to the working winding, supplying power to the starting winding and a common zero (or phase, depending on the circuit).
There are usually contact markings on the compressor housing or in the technical documentation. They are often designated by letters or symbols: C (Common - general), R (Run - working), S (Start - starting). Some circuits, especially European ones, use the designation L (Line) instead of a common contact. An incorrect connection will result in the engine either not starting or the starting winding burning out.
For clarity, consider the typical pinout of contacts for most single-phase compressors:
| Designation on the diagram | Contact function | Wire color (typical) | Position on triangle |
|---|---|---|---|
| C (Common) | Common power input | Black or White | Top or upper left |
| R (Run) | Working winding | Brown or Red | Bottom right |
| S (Start) | Start winding | Blue or Green | Bottom left |
| Grounding | Protective grounding housing | Yellow-green | Separate screw on housing |
When installing a new relay, it is important to observe the orientation. The relay body often has an arrow UP or inscription indicating that this side should face up. This is critical for induction relays where the movable core must move freely under the influence of gravity. If you install such a relay upside down, the contacts will not open after starting, and the starting winding will burn out.
For posistor relays, orientation in space is less critical, but it is still recommended to install them according to the factory markings. The contacts inside the relay should fit snugly around the compressor pins. If the contacts are oxidized or loose, they can be carefully tightened with pliers, but you must act carefully so as not to break the ceramic insulator.
Step-by-step instructions for replacing the relay
Start by dismantling the compressor protective casing. It is usually secured with latches or screws. Removing the cover gives you access to the rear of the motor. Carefully remove the terminal block from the compressor contact group. This may require slightly rocking it from side to side. Do not pull the wires, hold on to the plastic housing of the block.
Disconnect the wires from the old relay. In some models, the wires are inserted directly into the relay body, in others an intermediate block is used. If the wires are soldered, they must be carefully desoldered, first remembering or marking with a marker which wire went where. When installing a new relay, use crimp terminals for reliable contact; soldering is also acceptable, but requires skill.
Install the new start relay on the compressor contact group. It should fit tightly, with slight effort. Make sure the pins are fully seated in the holes. If the relay has a metal clip, secure it. Check the markings UP or TOPif required for your model.
Connect the wires to the corresponding terminals of the new relay according to the previously made diagram or photograph. Make sure that the wires do not touch hot parts of the compressor or each other in areas without insulation. Secure the wires with clamps, if necessary, so that vibration does not break the connection.
⚠️ Attention: It is strictly forbidden to turn on the compressor without the protective cover and grounding installed. This can lead to electric shock, since the compressor housing may become energized if the insulation breaks down.
After assembling all connections, turn on the refrigerator. Pay attention to the launch pattern. The engine should start with a characteristic hum, after 1-3 seconds there should be a quiet click of the starting circuit opening, and the compressor will go into smooth operation. If the start-up was successful, replace the protective cover.
Typical errors and troubleshooting
Even if you carefully follow the instructions, difficulties may arise. One of the most common mistakes is using a relay of the wrong power. If the relay is rated for less power than the compressor, it will overheat and quickly fail. If it is too high, the contacts may not close tightly enough for a reliable start, which will lead to a buzzing sound.
Often technicians forget to check the condition of the contact group on the compressor itself. If the pins are oxidized or burnt, the new relay will not work correctly. In this case, it is necessary to clean the contacts with fine sandpaper or a file, being careful not to damage the insulation around them. It is also worth checking whether the contact group itself is loose on the compressor terminals.
Sometimes the problem lies not in the relay, but in the thermal protection relay, which can be built into the overall design. If it is faulty, it will break the circuit immediately after turning on or prevent it from starting at all. Checking the integrity of the thermal relay with a multimeter is mandatory. In some cases, it is necessary to replace the entire unit (relay + thermal protection).
It is worth considering that the technical characteristics and designs of compressors may vary depending on the year of manufacture and manufacturer. For example, compressors Danfoss (now Secop) have their own connection features that differ from Italian Aspera or Chinese analogues. Always check the technical documentation for your specific model.
⚠️ Note: Technical standards and spare parts availability are subject to change. If you cannot find an exact analogue of the relay, consult with a specialist or refer to the official catalogs of manufacturers, since universal solutions may require modification of the circuit.
If, after replacing the relay, the compressor starts, but after a while it knocks out the protection again or stops cooling, the problem may be deeper. This may indicate a loss of freon, a clogged capillary system, or wear on the compressor itself. In such cases, simply replacing the electrics will not solve the problem completely.
Frequently asked questions (FAQ)
Is it possible to start a refrigerator without a starting relay?
Theoretically, you can start the engine by manually applying voltage to the starting winding, but this is extremely dangerous and is not recommended. Without a relay, the engine will not be able to switch to operating mode on its own and will burn out in a few seconds. It is impossible to operate a refrigerator without a working starting relay.
Why does a new relay burn out immediately after installation?
There may be several reasons: incorrect orientation of the relay (for induction), sticking compressor contacts, interturn short circuit in the motor windings or power surges in the network. It is also possible that a relay has been selected with unsuitable response current characteristics.
How to distinguish a posistor relay from an induction relay?
An induction relay is heavier, a knocking sound of the moving core is heard inside when shaken, and it has a strict installation orientation. The posistor is lighter, there are no moving parts inside (you can only hear the posistor if it dangles), and it is less sensitive to position in space, although it also has a recommended orientation.
How much does it cost to replace a starting relay?
The cost of the relay itself varies from 500 to 2000 rubles, depending on the model and manufacturer. If you do it yourself, the costs will be minimal. The replacement services will cost more, including the cost of spare parts and labor.
Can a universal relay be used?
Yes, there are universal starting relays that are suitable for a wide range of compressors. However, they may work less efficiently than the original ones and require careful selection of engine power. It is better to look for an original or a high-quality analogue for your refrigerator model.