The sudden stop of the refrigerator or strange clicking sounds often frighten the owners, but in many cases the reason lies in one small part - the start relay. This tiny component is responsible for starting the compressor, and its failure is one of the most common causes of refrigeration equipment stopping. Understanding how this unit works allows you not only to save on calling a technician, but also to quickly return the equipment to life by replacing an inexpensive spare part.
Symptoms of a malfunction can be different: from complete silence of the unit to chaotic attempts to start the engine, accompanied by a loud hum. Start relay is an electromagnetic or posistor mechanism that supplies the initial impulse to the motor windings. If this pulse does not arrive or is supplied incorrectly, the compressor cannot reach the required speed, and the protection system turns off the power to prevent the windings from burning out. That is why timely diagnosis is critically important.
Before disassembling the equipment, it is important to make sure that the problem really lies in the electrical part, and not in voltage surges or damage to the power cord. In this article, we will analyze in detail the physical signs of failure, instrumental testing methods and nuances that will help you accurately determine the condition of the device. Diagnostics requires care, but is quite within the capabilities of a person who knows how to use a multimeter.
Main signs of failure of the starting device
The first and most obvious signal of problems with the relay is the characteristic behavior of the compressor when the refrigerator is turned on. You may hear a loud click, followed by a motor hum for a few seconds, followed by another click and complete silence. This is a classic picture of how thermal relay overheating is triggered, since the engine cannot start due to the lack of a starting impulse. The cycle can be repeated endlessly until you disconnect the device from the network.
In some cases, the opposite situation is observed: the refrigerator is working, but the compressor is very hot, and the temperature inside the chambers is not low enough. This may indicate that the contacts inside the relay are burnt out and do not provide a full connection, which is why the motor is overloaded. It is also worth paying attention to the appearance of the part: if traces of soot, plastic melting are visible on the body, or a burning smell is felt, then visual inspection already gives a definite answer - the part requires replacement.
Another sign is the absence of a characteristic click when turned on. When in good condition, you will usually hear a slight knocking sound as the contacts close. If, when voltage is applied, there is silence and the compressor does not make any sounds, the control circuit may be broken or the electromagnet coil may have burned out. It is important not to ignore these signals, since constant attempts to start can damage the compressor itself, the repair of which will cost much more.
- 🔊 Loud clicks and humming followed by the motor turning off.
- 🔥 Strong heating of the compressor housing when the cooling is not working.
- 👃 Burning smell or visible traces of melting on parts.
- 🔇 Complete lack of engine response when plugged in.
⚠️ Attention: If you smell burnt wiring or see sparking, immediately disconnect the refrigerator from the power supply. Operation of faulty electrical equipment may result in a short circuit or fire.
It is also worth noting that symptoms may vary depending on the type of protection installed. Older models often use electromechanical systems, where contact wear occurs gradually. In modern units with electronic control, a relay breakdown may be accompanied by an error code displayed on the display, although this happens less frequently. Diagnostics It should always begin with a visual inspection and listening to the operation of the unit.
Types of starting relays and their design features
To correctly determine the malfunction, you need to understand what type of device is installed in your refrigerator. There are two main types: electromagnetic and posistor. An electromagnetic relay works on the basis of an inductance coil: when current passes through the starting winding, a magnetic field is created, which draws in the core and closes the contacts. After the motor starts, the current drops, the core drops, and the circuit opens. Such devices often have moving elements that can jam or wear out.
Posistor relay (or thermal start) has no moving parts. Its key element is a thermistor (posistor), which at room temperature has low resistance and allows current to pass through. When heated by passing current, its resistance increases sharply, actually breaking the starting winding circuit. This is a more reliable design, but is sensitive to overcurrent. If a posistor is “broken,” it remains conductive; if it “burns out,” it becomes a dielectric.
You can determine the type of relay by its appearance and markings. Electromagnetic devices often have a more massive body and the core can be heard moving inside when shaken. PTCs are usually more compact, lighter and do not have moving mechanical parts. There are also combined devices where the starting relay is combined with a thermal protective relay in one housing. In such cases, if one element breaks down, the entire unit is often replaced for reliability.
How to distinguish a posistor from an electromagnet?
An electromagnetic relay inside has a copper coil and a movable metal core, which can be seen by removing the cover. A posistor is a ceramic disk or tablet filled with a compound and has no moving parts.
Knowing the type of device helps you choose the right testing strategy. For electromagnetic systems, the mobility of the core and the integrity of the coil are critical. For posistor - resistance at different temperatures. Fault one type does not always mean a breakdown of the other, although the symptoms may be similar. Always check the markings of the new part with the old one before purchasing.
Visual diagnostics and external inspection of the part
The first stage of testing should always be visual, as it allows you to identify up to 50% of all possible problems without the use of tools. After unplugging the refrigerator and removing the protective cover at the back of the unit, carefully remove the relay. It is usually attached to the three contacts of the compressor and is held in place by a spring clip or screws. Carefully inspect the case for cracks, swelling or signs of thermal effects.
Pay special attention to the contact groups. If you see black deposits, oxidation or melted plastic around the terminals, this is a sure sign that excess current was passing through the device or there was poor contact. Oxidation contacts increases resistance, which leads to heating and eventual failure. Also check the condition of the wires going to the relay: they should not be brittle, have cracked insulation or signs of a short circuit.
Try to gently shake the relay near your ear. If something rattles or knocks inside, this may mean that the ceramic posistor has collapsed or the electromagnet core has broken off. In good condition, the device should be solid and not make sounds when shaken lightly. However, the absence of sound does not guarantee serviceability, so a visual inspection is only the first step.
- 👀 Inspect the case for cracks and melting.
- 🔌 Check the contacts for carbon deposits and oxidation.
- 👂 Shake the device: there should be nothing inside audible.
- 🧵 Assess the insulation condition of the suitable wires.
⚠️ Attention: Before removing the relay, be sure to photograph the wire connection diagram. By mixing up the contacts during assembly, you can burn the new component or damage the compressor windings.
If there are no visual defects, this does not mean that the device is working properly. Internal breaks or changes in the resistance of the posistor cannot be seen with the eye. Therefore, let's move on to an instrumental check. Multimeter will become your main assistant at the next stage.
Instrumental check with a multimeter
For accurate diagnostics, you will need a multimeter (tester) in resistance measurement mode (Ohms). Make sure the relay is completely cool before starting measurements, especially if you have just removed it from a running (or attempting to run) compressor. For posistor relays this is critically important, since their resistance depends on temperature. In a cold state, a serviceable posistor should show a resistance in the range of 10-50 Ohms (the exact value depends on the model).
Checking an electromagnetic relay involves checking the continuity of the coil. Connect the tester probes to the coil contacts. The device must show a certain resistance (usually from 30 to 300 Ohms, depending on the model). If the multimeter shows “infinity” (one in the most significant digit or OL), it means there is a break in the coil and the relay is not working. If it shows zero, a short circuit has occurred in the turns. Also check the contacts: in the initial position they can be open or closed depending on the design, but when voltage is applied (which is difficult to check at home without a stand), they should change state.
For a posistor relay, the technique is different. Measure the resistance between the main contacts. It should be small (the same 10-50 Ohms). Then you can try to gently heat the case with a hairdryer (not an open flame!) and measure the resistance again. When heated, a working posistor should sharply increase the resistance to several megaohms (actually break the circuit). If the resistance does not change or remains low even after heating, the part is faulty.
☑️ Check with a multimeter
It is also important to check the thermal relay, if it is built-in or comes as a separate “pill”. It is a bimetallic plate. When cold, it should “ring” (show zero or very low resistance). If the circuit is broken immediately, the protection is burned out. However, you cannot simply replace the thermal relay; you need to find the reason why it worked (overload, jammed compressor).
| Check type | Normal reading | Fault symptom | Probable cause |
|---|---|---|---|
| Resistance of the posistor (cold) | 10 - 60 Ohm | Infinity or 0 Ohm | Open circuit or short circuit |
| Coil resistance (electro) | 30 - 300 Ohm | Infinity | Open coil winding |
| Thermal relay contacts | 0 - 1 Ohm | Infinity (cold) | Bimetallic plate burned out |
| Insulation check | Infinity | Any value | Insulation breakdown on the body |
If your measurements coincide with the “Symptom of Malfunction” column, then the part definitely requires replacement. Do not attempt to repair burnt-out internal relay components - this is impractical and unsafe. The cost of a new spare part is low, and the reliability of the factory product is guaranteed.
Causes of frequent breakdowns and relay burnouts
Simply replacing a burnt-out relay is half the battle. In order for a new part to last a long time, you need to understand why the previous one failed. The main reason is unstable voltage in the electrical network. Voltage surges lead to a sharp increase in the inrush current, which causes overheating and degradation of the contacts or breakdown of the posistor. If lights in your home often flicker or light bulbs flicker, you should think about installing a voltage stabilizer for your refrigerator.
The second common reason is problems with the compressor itself. If the motor is worn out, jammed or has an interturn short circuit, it consumes increased current when starting. Start relay in this case, it takes the blow on itself, trying to start the “heavy” motor, and burns out. Therefore, if after replacing the relay the situation repeats after a short time, the problem is deeper and lies in the compressor.
The third factor is natural wear and tear and aging of materials. Over time, the contacts burn out, the plastic dries out, and the posistor changes its properties. This is a normal process of operation, especially in conditions of continuous operation 24/7. The quality of the spare part itself also affects: cheap analogues may not withstand the declared loads.
Do not forget about external factors: vibration, dust, high humidity in the refrigerator installation room can accelerate corrosion of contacts and destruction of internal elements. Regular cleaning of the rear grille of the refrigerator helps maintain the normal operating temperature of the components.
Replacing the relay: step-by-step instructions and safety measures
The process of replacing the start relay is quite simple and does not require special skills other than basic caution. The main rule is to complete shutdown equipment from the mains. Do not attempt any manipulation while the cord is plugged into the outlet. Also allow the compressor to cool down if it has been running recently to avoid getting burned.
Remove the cardboard or plastic cover on the back of the refrigerator that covers the compressor. You will see a black motor "tank" that has a relay attached to it. Carefully disconnect the wire terminals (after photographing their position!). Remove the retainer (spring or screw) and pull the relay off the compressor contacts. Sometimes it can fit tightly - do not pull sharply, it is better to slightly rock it from side to side.
Install the new part in the reverse order. Make sure that it fits tightly and all the way, the contacts fit into the grooves of the compressor without distortion. Secure the clamp and connect the wires according to the photo taken earlier. Plug in the refrigerator and listen: there should be a click, then the hum of the compressor, and after 10-20 seconds it should start working smoothly. If you hear a crackling sound or the buzzing stops after 3-5 seconds, turn it off immediately, there is an error in the connection or a defective new spare part.
⚠️ Attention: Technical characteristics and methods of mounting the relay may vary depending on the manufacturer (Indesit, Atlant, Bosch, LG). Always check the markings of the new part with the original. Using an unsuitable relay may damage the compressor.
After successful startup, check the operation of the refrigerator within a few hours. It should reach temperature and turn off normally. If everything went well, you saved a significant amount on calling a technician and gained useful experience.
Can a burnt relay be repaired or does it only need to be replaced?
In 99% of cases, the relay must only be replaced. The internal elements (posistor, coil, contacts) are filled with compound or compressed, and their restoration at home is impossible. Attempts to clean the contacts or glue the housing are temporary and dangerous.
Why did the new relay burn out immediately after installation?
Most likely, the problem is not in the relay, but in the compressor (interturn short circuit, wedge) or in a serious power surge in the network. There may also be an error when connecting the wires. Motor diagnostics are required.
Where can I find the relay markings to buy an analogue?
The markings are usually applied to the side or top edge of the relay body. Look for a combination of letters and numbers (eg RT, RAT, PTC). You can also find the spare part number in the technical documentation for your refrigerator model.
Does room temperature affect the operation of the relay?
Yes, indirectly. In a very hot room, the compressor works harder, turns on more often and runs longer, which accelerates wear on the starter. In the cold (below +10°C), the oil in the compressor thickens, starting is difficult, which can also lead to the relay burning out.
How long does a starting relay last on average?
The average service life of a high-quality relay is 5-10 years. However, with frequent power surges or power outages, it can fail much earlier. PTC relays are considered more durable than electromagnetic relays.