A sudden stop of the compressor often becomes an unpleasant surprise for the owner of household appliances, leading to food damage. In most cases, the cause of failure is not the motor itself, but a failed starting or thermal relay, which is responsible for protecting the motor from overloads and overheating. Understanding the operating principle of this unit and the ability to carry out its initial diagnostics allows you to save significant money on calling a technician and quickly bring the refrigerator back to life.
Before proceeding with disassembly, you must clearly understand that thermal relay is a safety mechanism that breaks the circuit when the temperature or current rises critically. If this element is faulty, it will either not turn on the motor or will not protect it in the event of an accident, which can lead to burnout of the compressor windings. Therefore, correct and timely testing is a key step in the repair of any model of refrigeration unit, be it Indesit, Bosch or Atlant.
In this article we will analyze in detail the design of protective mechanisms, consider the signs of their breakdown and provide a step-by-step diagnostic algorithm using a multimeter. You will learn to distinguish a real malfunction from false alarms and understand when a part requires replacement, and when the problem lies deeper.
Signs of a faulty protective mechanism
You can determine that the problem lies in the relay by the characteristic external signs that appear when operating or attempting to start the refrigerator. Most often, users are faced with a situation where the compressor tries to start, makes a short beep or click, and then immediately goes silent. After some time, the cycle repeats, which indicates that the protection has tripped or the engine cannot be started.
Another striking symptom is the complete absence of sound from the running motor when the refrigerator is plugged in, although the light in the chamber is on. In this case start relay it may be completely broken or have oxidized contacts that do not allow current to pass through. It is also worth paying attention to the temperature of the compressor housing: if it is excessively hot to the touch, but does not work, there is a high probability that the thermal protection is not reset or is activated instantly.
Sometimes the malfunction manifests itself in the form of a characteristic burning smell or melted plastic in the area of the engine compartment. This indicates that the contacts inside the relay may have burned out due to arcing, causing conduction failure. A visual inspection in this case will often reveal a blackened housing or traces of soot on the terminals.
⚠️ Attention: If you hear a loud cracking sound or see sparking inside the engine compartment, immediately unplug the refrigerator. Operating equipment with faulty electrics can lead to a fire.
Design and principle of operation of the relay
For proper diagnostics, you need to understand how this unit works. Modern refrigerators often use a combined device that combines the functions of starting and thermal protection, but the principle of their operation differs. Start relay It is an electromagnetic or posistor mechanism that briefly supplies voltage to the starting winding of the motor to create torque.
Thermal protection, in turn, works on the basis of a bimetallic plate. When an electric current passes through it, the plate heats up and, having reached a certain temperature, bends, opening the contacts and stopping the engine. After cooling, the plate returns to its original position, closing the circuit again. This cycle ensures safe operation of the motor within acceptable temperature limits.
In older models of refrigerators, such as some series ZIL or Minsk, there may be separate protection units attached directly to the compressor housing. In new units, for example LG or Samsung, compact posistor starters are more often used, which do not have moving mechanical parts, but are also subject to failure.
The difference between posistor and electromagnetic relay
A posistor relay works by changing the resistance of the crystal when heated by current, has no moving parts and is considered more reliable, but expensive. Electromagnetic relays use a coil and a moving core; they are cheaper, but over time they can stick or wear out mechanically.
Necessary tools for diagnostics
A high-quality check is impossible without a basic set of tools, which any home craftsman should have on hand. The main device for diagnosing electrical circuits is multimeter (tester). With its help, you can ring the windings, check the integrity of the contacts and measure the resistance, which will give an accurate answer about the condition of the part.
You will also need a set of screwdrivers (phillips and flat) to dismantle the protective cover of the engine compartment and remove the relay itself. Pliers for careful removal of the terminals and, possibly, fine-grained sandpaper for cleaning the contacts will not be superfluous if you plan to restore the part, although in the case of thermal relays replacement is more often recommended.
- 🛠️ Multimeter with the function of continuity and resistance measurement
- 🔧 A set of screwdrivers of various sizes and form
- 🧤 Dielectric gloves for safety
- 📸 Smartphone (for photographing the connection diagram before removal)
It is important to make sure that your multimeter is working and has a charged battery, since readings with a discharged battery may be incorrect. Before starting work, be sure to disconnect the refrigerator from the electrical outlet by removing the plug from the socket to eliminate the risk of electric shock.
Removal and visual inspection
The inspection process begins by gaining access to the compressor, which is usually located in the lower rear part of the refrigerator. Remove the back metal or cardboard panel by removing the retaining bolts or latches. You will see a view of the motor-compressor with a protective starting block attached to its terminals.
Carefully remove the plastic casing, if any, and disconnect the connector with wires. Pay attention to exactly how the relay is secured: in some models it is simply put on the compressor bayonets, in others it is fixed with a metal bracket or clamp. Before removing, be sure to photograph the location of the wires so that during assembly you do not confuse the polarity or purpose of the contacts.
After removing the part, perform a thorough visual inspection. Look for signs of soot, carbon deposits, melted plastic, or corrosion on the metal contacts. If a blackened posistor or burnt contacts are visible inside the relay housing, further checking may no longer be necessary - the part requires replacement. Also check the integrity of the bimetallic plate, if it is visible: it should not have cracks or signs of severe overheating.
Instructions for checking with a multimeter
The most reliable way to determine the condition of a relay is to check its electrical parameters using a multimeter. Switch the device to resistance measurement mode (Ohm) or continuity mode. If you are checking thermal protection, connect the probes to its terminals: a working “heater” in a cold state should show zero resistance (short circuit), since the contacts are closed.
To check the starting relay with a posistor, measure the resistance between the corresponding contacts. The normal value for a working posistor is usually from 3 to 16 ohms, depending on the model and manufacturer. If the device shows infinity (break) or the resistance differs significantly from the nominal value, the part is faulty.
When diagnosing electromagnetic relays, you must also check the coil for a break. The winding resistance must be within the specified values. If the multimeter shows “1” or “OL” (Over Limit) at the measurement limit, then the circuit inside is open. Also check the contacts for a short to the body: the resistance between any terminal and the metal body of the relay should be infinite.
☑️ Test algorithm with a multimeter
If after checking it turns out that the thermal protection does not “ring” (resistance is infinite) in a cold state, this means that the bimetallic plate has lost its elasticity or the contacts are burnt and do not close. In this case, the relay will not start the compressor, even if the motor itself is working.
Table of typical resistance values
For ease of diagnosis, below is a table with approximate resistance values for various types of relays found in household refrigerators. Remember that the exact parameters may vary depending on the manufacturer and the specific series of equipment.
| Relay type | Normal resistance (Ohm) | Fault symptom | Manufacturers |
|---|---|---|---|
| Posistor (starting) | 3.5 – 16.0 | Open (>1000) or short circuit (0) | Electrolux, Beko, Indesit |
| Thermal protection | 0 (shorted in cold) | Infinity in cold | Universal |
| Electromagnetic | 30 – 100 (coil) | Break coil winding | Atlant, Minsk |
| Combined | Depends on the circuit | Lack of conductivity through the circuits | LG, Samsung |
Use these data as values. If your measurements differ radically from those listed, there is a high chance that the part is defective. However, even if the resistance is normal, the relay may not work under load due to loss of contact pressure or deformation of the plate.
Replacement and precautions
If the diagnostics confirmed a malfunction, the only correct solution would be to replace the relay with a similar one. You must select a new part strictly according to the markings of the old one or according to the compressor model. Installing the wrong relay can result in the engine not starting or, worse, burning out due to improper operation of the protection.
When installing a new element, make sure that it sits tightly on the compressor terminals and is locked in the correct position (usually the arrow or inscription UP should face up). Incorrect orientation may impair the operation of mechanical parts or thermal protection. After installation, reassemble everything in the reverse order and turn on the refrigerator.
⚠️ Attention: Do not try to repair the thermal relay by stripping the contacts or flattening the plate. This disrupts the calibration of the protection, and the next time the compressor overheats, it may burn out irrevocably.
After replacing and turning on, listen to the operation of the motor. The launch should be confident, without prolonged beeps or clicks. If the compressor started working and began to gain cold, it means the repair was successful. If the problem persists, the compressor itself may be faulty or there are problems with the wiring.
Frequently asked questions (FAQ)
Is it possible to start a refrigerator without a relay?
Theoretically, you can start the engine by applying voltage directly to the windings, but doing this is strictly not recommended for constant operation. Without thermal protection, the compressor may burn out at the first overheat or jam, since there will be no emergency shutdown.
Why does a new relay burn out immediately after installation?
A common reason is a malfunction of the compressor itself (turn-to-turn short circuit), which causes consumption currents to increase, or problems with the thermostat that force the motor to work non-stop. Also, the cause may be unstable voltage in the network.
How to distinguish a starting relay from a thermal one?
A starting relay usually has a more complex design with a coil or posistor and is connected to the starting winding. The thermal relay is often a simple bimetallic element in a plastic case, placed directly on the compressor terminals in series with the working winding. In modern models, they are often combined into one unit.
How much does it cost to replace a relay in a service?
The cost consists of the price of the part itself (usually from 500 to 2000 rubles, depending on the model) and the work of the technician. Self-replacement allows you to save on the cost of services, since the procedure does not require complex equipment.