Sudden stoppage of the compressor and silence in the kitchen instead of the usual humming often indicate a failure of the start-up relay. It is this small but critical element that is responsible for starting the engine and protecting it from overloads. If the refrigerator has stopped freezing and the motor does not make any sounds or, conversely, hums and clicks, but does not start, then first of all you should check the starting circuit. Many owners of household appliances Indesit, Atlant or LG try to solve the problem by calling a technician, although diagnostics are often possible even for a beginner with a basic set of tools.
The process of checking a relay requires a minimum set of tools, the main one of which is a multimeter. Understanding the operating principle of this unit will help you not only save on service center services, but also quickly bring your equipment back to life. In this article we will analyze in detail the relay device, the symptoms of its failure and a step-by-step diagnostic algorithm. It is important to understandthat ignoring the malfunction can lead to more serious damage, even burning out the compressor windings, so you should not delay checking.
Before you start disassembly, you need to make sure that the problem lies in the relay, and not in the lack of voltage in the network or a breakdown of the thermostat. Often users confuse the symptoms, believing that the motor itself has broken down, when the culprit is a cheap part. We will look at how to distinguish a relay malfunction from other problems and how to correctly measure resistance. The critical point is to completely disconnect the device from the power supply before starting any work with electrical components.
Design and principle of operation of a starting relay
A starting relay is an electromechanical switch, which closes the circuit of the compressor starting winding only at the moment of start. As soon as the motor rotor reaches the required speed, the current in the circuit drops and the relay opens the contacts, leaving only the main winding to work. In modern refrigerators, electromagnetic and posistor devices are most often found. Electromagnetic models operate due to the magnetic field of the coil, which draws in the core and closes the contacts, while posistor models use the property of the semiconductor material to change resistance when heated.
Structurally, the relay consists of a housing, an inductor (in electromagnetic models), a movable core, a contact group and, in some cases, a bimetallic plate for thermal protection. When voltage is applied, the current passes through the coil, creating a magnetic field. Current strength at the moment of start-up, it is significantly higher than the nominal one, which allows the magnet to overcome the resistance of the spring and close the circuit. If the motor does not start or a short circuit occurs, the current increases even more, heating the bimetallic plate, which opens the circuit, preventing the windings from burning out.
Posistor relays, often used in models Bosch i Siemens, work on a different principle. Inside them is a disk of barium titanate, which at room temperature has low resistance and allows current to pass through. When current passes, the disk heats up, its resistance increases sharply, and the current through the starting winding practically stops. This is a more reliable system with no moving mechanical parts, but it is also susceptible to aging and breakdown from overheating. Understanding your relay type is important for proper diagnosis.
⚠️ Attention: Residual charges may accumulate inside the relay, and the contacts may be hot immediately after attempting to start. Always let the equipment cool down and make sure there is no voltage before touching the internal components.
Typical symptoms of a relay malfunction
You can determine that it is the starting relay that has failed by the characteristic signs that appear immediately after turning on the refrigerator. The most common symptom is a distinctive clicking sound, followed by a humming sound from the compressor that lasts a few seconds, followed by a second clicking sound and silence. This cycle can be repeated at regular intervals until the thermostat cuts off power to the compressor to prevent overheating. Such symptoms indicate that the starting winding is not connected or the engine cannot gain speed.
Another sign is the complete lack of reaction of the refrigerator when turned on: no hum, no vibration, although the light in the chamber is on. In this case, the relay could simply “stick” in the open state or burn out completely. 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 the diagnosis is obvious without additional diagnostics. Visual inspection Often allows you to immediately identify the problem, especially if the relay has been in use for a long time.
Sometimes the refrigerator may work, but with interruptions: do not reach the temperature for a long time or switch off frequently. This may indicate that the thermal protection of the relay has become too sensitive and is triggering prematurely, preventing the compressor from reaching operating mode. In such cases, replacing the relay often solves the problem of unstable operation. If the compressor hums, but does not start even after replacing the relay, the problem may lie in a jammed motor itself or an interturn short circuit.
Preparation for diagnostics and the necessary tools
To carry out high-quality diagnostics, you will need a minimum set of tools that most home craftsmen can find. The main device is a multimeter (tester), which allows you to measure resistance and test circuits for integrity. You will also need screwdrivers (Phillips and flathead) to remove the back cover and dismantle the compressor casing, pliers to carefully remove the terminals and, possibly, a knife to clean the contacts if they are oxidized. It is a good idea to have isopropyl alcohol on hand to clean contacts from carbon deposits.
Before starting work, it is necessary to ensure safe conditions. The refrigerator should be unplugged by unplugging the cord from the outlet. Then you need to move the unit away from the wall to gain free access to the rear panel. Remove the metal or plastic cover covering the compressor compartment. It is usually secured with latches or several screws. Be careful not to damage the condenser tubes located nearby.
☑️ Checklist for preparing for repairs
After removing the cover, find the compressor - this is the black “barrel” at the bottom of the rear wall. At its end or side there is a plastic casing in which the relay is located. It is this detail that we have to extract and check. Before removing the relay, it is recommended to photograph the position of the wires and terminals so as not to mix up the contacts during assembly. Although the connection diagram is standard, reinsurance is never superfluous, especially for models Stinol or Beko, where the layout may differ.
Step-by-step instructions: how to remove and disassemble the relay
Removing the relay is a simple process, but it requires accuracy. First you need to remove the retaining bracket or strip that presses the relay housing to the compressor terminals. It can usually be removed with a slight movement of pliers or a screwdriver. After this, the relay can be pulled down, removing it from the three pins of the compressor. Do not pull sharply so as not to break the wires going to the terminals.
If the wires are connected directly to the relay through connectors, they must be carefully disconnected, holding the collets with pliers. In some models, for example, in old refrigerators ZIL or Minsk, the wires may be soldered. In this case, you will need a soldering iron to disconnect, but most often removable terminals are used. After removing the relay from the compressor casing, you can begin disassembling it. The case usually consists of two halves, fastened with latches.
Carefully pry off the housing with a flat-head screwdriver at the junction of the halves. Inside you will see a coil, a core, a contact group and a posistor (if the relay is combined). Inspect the insides for obvious defects: blackening, melting of plastic, destruction of the ceramic element. If there are no visual defects, we proceed to instrumental inspection. It is important not to lose small parts, such as springs or the core, during disassembly.
⚠️ Attention: When disassembling an electromagnetic relay, monitor the position of the movable core. If it falls out or is lost, it will be extremely difficult to assemble the relay back into working condition, and the part will have to be replaced.
Diagnostics with a multimeter: checking circuits and contacts
Testing a relay with a multimeter is the most reliable way to determine its performance. Switch the device to resistance measurement mode (Ohm) to the limit of 200 Ohm or 2 kOhm. First check the solenoid coil circuit. Connect the multimeter probes to the contacts that correspond to the terminals of the main winding of the compressor (usually they are located vertically). The device should show a resistance in the range from 3 to 15 ohms, depending on the model. If the resistance is infinitely high (open) or zero (short circuit), the coil is faulty.
Then check the starting circuit contacts. In a cold state (when the posistor has cooled down), the resistance between the contacts of the starting winding should be low (several ohms) for electromagnetic relays or about 20-50 ohms for posistor relays. If the multimeter shows one (open) in the circuit where there should be resistance, then the circuit is open. It is also necessary to ring the thermal protection (bimetallic plate). The resistance should be close to zero. If the circuit does not ring, the protection is burnt out or the contacts are oxidized.
To be completely sure, you can carry out a “hearing” and vibration test. Apply 220V voltage to the relay input contacts (using extreme caution!). A working electromagnetic relay should make a distinct click when the core retracts. If there is no click and the coil is working properly, it means that the mechanism is jammed or the contacts are burnt out. When voltage is applied, posistor relays begin to quietly crackle and heat up - this is a normal operating process.
The nuances of checking a posistor
A posistor is a temperature-sensitive element. It makes sense to check its resistance only when it has completely cooled down. If you apply voltage to a hot posistor, it may not allow current to pass through, since it is already in a state of high resistance. Allow the part to cool for 15-20 minutes before testing.
The table below provides estimated resistance values for different types of relays to help you interpret multimeter readings:
| Relay Type / Element | Normal Resistance | Symptom of malfunction | Action |
|---|---|---|---|
| Electromagnet coil | 3 – 15 Ohm | ∞ (infinity) or 0 Ohm | Replacing the relay |
| Thermistor (cold) | 10 - 50 Ohm | ∞ (break) | Replacing the posistor or relay |
| Thermal protection | 0 - 1 Ohm | ∞ (no contact) | Replacement of thermal protection |
| Starting circuit contacts | 0 Ohm (closed) | ∞ (open at rest) | Cleaning or replacement |
Replacement of the relay and final assembly of the refrigerator
If the diagnostics showed a malfunction, the relay must be replaced. The selection of an analogue is carried out according to the markings indicated on the body of the old part, or according to the compressor model. Universal relays are suitable for many models, but it is better to look for an original or a high-quality analogue from well-known brands, such as Danfoss or Secop. Installation of a new part is carried out in the reverse order of removal. Push the relay onto the compressor pins until it stops, making sure that it is seated tightly and evenly.
Fasten the fixing bracket and connect the wires to the terminals according to the previously taken photograph or diagram. Make sure all connections are secure and not loose. After installing the relay, replace the compressor protective cover and secure it. Now you can carefully install the back metal cover of the refrigerator in its place and secure it with screws or latches.
After complete assembly, turn on the refrigerator. Listen: a characteristic start-up click should be heard, and the compressor will begin to hum evenly. Within 10-15 minutes, check whether the evaporator inside the chamber begins to cool. If the cold has started and the compressor operates without cyclic stops and clicks, it means the repair was successful. If the problem persists, perhaps the fault lies deeper - in the compressor itself or the control system.
⚠️ Attention: After replacing the relay, do not load the refrigerator with food immediately. Let it run idle for 1-2 hours to ensure stable operation and reach operating temperature.
Frequently asked questions (FAQ)
Is it possible to repair a burnt-out relay yourself or just replace it?
In most cases, relays are non-separable or their repair is not economically feasible. If a coil burns out or a posistor breaks, it is easier and more reliable to buy a new part. Cleaning the contacts is only possible if the relay can be easily disassembled and the damage is minimal, but this is a temporary measure.
Why does a new relay burn out a short time after replacement?
A common reason is a jammed compressor. If the motor cannot turn over, the starting current remains high for too long, causing the new relay to overheat and burn out. Also, the cause may be a malfunction of thermal protection or problems with the voltage in the network.
Is a universal relay suitable for an old-style refrigerator?
Universal relays are often suitable for replacement, but it is important to match the compressor power and the type of refrigerant. Older models with R12 freon and modern ones with R600a may require different starting torque characteristics. It is better to select an analogue strictly according to the compatibility catalog.
Is it dangerous to operate a refrigerator with a faulty relay?
Yes, it is dangerous. In addition to food spoilage, a faulty relay can lead to overheating of the wiring, melted insulation, and even a fire. In addition, constant attempts to start “kill” the windings of the compressor, making its repair impossible.