A sudden stop in the operation of the refrigerator or, conversely, its continuous hum without cooling often confuses the owner. If you notice that the compressor hums only for a split second and clicks, or is completely silent, in 80% of cases the start-up relay is to blame. This small element is responsible for starting the engine and protecting its windings from overheating, being a critical component of the entire system.
Before calling a technician or buying a new unit, it makes sense to conduct independent diagnostics. Understanding how the part works and how to identify if it is faulty will save you a significant amount of money and time waiting for repairs. In this article, we will analyze the relay design, methods for checking it with a multimeter, and visual signs indicating the need for replacement.
It is worth noting that not all breakdowns require sophisticated equipment. You can often tell if a component is malfunctioning by its characteristic sounds or appearance. However, for an accurate diagnosis you will need a basic set of tools and knowledge of safety precautions when working with electricity.
Design and principle of operation of a starting relay
A starting relay is an electromechanical switch that controls the supply of voltage to the compressor motor windings. When the refrigerator is turned on, the motor rotor is motionless, and to start it, a significant current is required, which is supplied to the starting winding. As soon as the shaft reaches the required speed, the relay opens the starting winding circuit, and the engine continues to operate on the main one.
The second important function is thermal protection. Inside the case there is a bimetallic plate that reacts to rising temperatures. If the compressor overheats due to prolonged operation or cooling problems, the plate bends and opens the contacts, completely de-energizing the unit. It is this dual function makes the relay an indispensable safety element.
There are two main types of devices: induction (electromagnetic) and posistor. Induction models use a coil to create a magnetic field that draws in the core and closes the contacts. The posistor relays, more modern, use a ceramic element that changes its resistance when heated by current, gradually opening the starting winding circuit.
Incorrect operation of any of these mechanisms leads to the fact that the compressor either cannot start or operates with overload, which can ultimately damage the motor-compressor itself.
Visual diagnostics and external signs of failure
The first stage of testing should always be an external inspection. Even without opening the refrigerator case, you can notice a number of alarming symptoms indicating a relay malfunction. If you hear a characteristic click, followed by a buzzing sound that lasts 3-5 seconds, and again a click that fades away, this is a classic sign that the trigger mechanism is not working.
It is also worth paying attention to the temperature of the case. If the compressor is very hot to the touch, but no cold is generated inside the chamber, this may indicate that the engine is trying to start but is stuck in the starting phase. In such cases, the thermal protection often kicks in and the unit shuts down for a long time until it cools down.
⚠️ Attention: If you smell something burning or see smoke coming from the back of the unit while the refrigerator is running, immediately unplug the appliance. Further operation may lead to a fire or complete failure of the compressor.
For deeper diagnostics, it is necessary to remove the relay. It is usually mounted on the side of the compressor and covered with a plastic cover. After removing the casing, inspect the unit itself: there should be no cracks, traces of melting or soot on it. If you see blackened contacts or a deformed case, further checking with a multimeter may no longer be necessary - the element definitely requires replacement.
Why does the relay burn out?
A frequent cause of failure is unstable voltage in the network or long-term power outages. Also, the relay can burn out if the compressor is overloaded due to a freon leak or a clogged capillary system.
Necessary tools for checking the relay
For high-quality diagnostics, you will need a minimum set of tools that most home craftsmen can find. The main device will be a multimeter (tester), which allows you to measure resistance and test circuits for breaks. Without this device, it is almost impossible to carry out an accurate check.
In addition to the multimeter, prepare the following accessories:
- 🔧 Screwdriver (Phillips or flat) for removing the protective cover and terminals.
- 🧤 Dielectric gloves for protection against residual voltage.
- 🔦 Flashlight for better illumination of the working area in the compressor niche.
- 🧹 Soft brush for cleaning contacts from dust and oxides.
It is important that the multimeter probes are in good working order and that the battery in the device is not discharged, otherwise the readings may be incorrect. Before starting work, make sure that the refrigerator is completely disconnected from the power supply.
☑️ Checking readiness for diagnostics
Step-by-step instructions: how to remove and disassemble the relay
The process of dismantling the relay is quite simple, but requires care. First, move the refrigerator away from the wall to allow easy access to the rear panel. Remove the cardboard or metal cover covering the compressor area.
Find the compressor itself - this is a black barrel-shaped cylinder at the bottom of the unit. On the side (or top, depending on the model) you will see a small box where the wires fit. This is our relay. It can be attached with latches, screws, or simply put on the contacts of the compressor.
Proceed according to the following algorithm:
- Take a photo of the location of the wires before disconnecting, so as not to mix up the contacts during assembly.
- Remove the fixing bracket or bar, if it available.
- Carefully pull the relay down or to the side, removing it from the three pins of the compressor.
- Disconnect the wires that go to the relay terminals, having previously noted their colors.
Now that you have the relay in your hands, you can start disassembling it. The case usually consists of two halves, held together by plastic latches. They need to be carefully loosened with a screwdriver. Inside you will see a coil, a core, contacts and, possibly, a posistor.
Checking the relay with a multimeter: measuring resistance
The most reliable way to check the serviceability of the part is to measure the resistance of the windings and contacts using a multimeter. Switch the device to the resistance measurement mode (Ohm) for a range of up to 2 kOhm.
For induction relays, the test is carried out as follows:
- 📏 Checking the coil: Attach the probes to the coil contacts. The resistance should be within normal limits (usually from 30 to 200 Ohms, the exact values depend on the model). If the device shows infinity (open circuit) or zero (short circuit), the coil is faulty.
- 📏 Checking the contacts: In a quiet state, the contacts of the starting winding should be open. If the multimeter beeps when testing these contacts, it means that they are stuck and the relay requires replacement.
- 📏 Thermal relay: Check the integrity of the bimetallic plate. The resistance should be close to zero. If the circuit is open at room temperature, the thermal protection is faulty.
For posistor relays, the technique is slightly different. The posistor in a cold state should have low resistance (20-50 Ohms). If you heat it up with a hairdryer, the resistance should rise sharply to several megaohms. If the resistance does not change or is initially equal to infinity, the element has burned out.
Below is a table of typical resistance values for different types of relays:
| Relay type | Coil/posistor resistance | Contact state (at rest) | Probable malfunction |
|---|---|---|---|
| Induction | 30-150 Ohm | Open | Coil break |
| POSISTOR | 20-50 Ohm (cold) | Closed (via POSISTOR) | POSISTOR burned out |
| Thermal protection | 0 Ohm (almost) | Closed | Open protection circuit |
| Any type | Infinity | Any | Complete failure |
⚠️ Attention: The technical characteristics of the relay may vary depending on the compressor manufacturer (Danfoss, Secop, Atlant). Always check the received data with the markings on the body of the part or the technical documentation of the specific refrigerator model.
Alternative methods of checking and replacement
If you don’t have a multimeter at hand, you can use the elimination method, although it is less accurate and requires caution. You can try to gently shake the relay near your ear. If the ringing of a fallen part is heard inside, it means that the mechanical part is destroyed or the coil has become detached from the core.
Another way is to test it by connecting a known-good relay from another refrigerator with similar parameters. If, when installing a new part, the compressor starts and the refrigerator begins to freeze, then the problem was in the relay.
When replacing, it is important to choose an analogue. The markings are usually applied to the body. You need to search by model number or technical parameters (starting current, compressor type). Universal relays often come complete with adapters for different types of compressors.
The process of installing a new element:
- 🔌 Place the relay on the compressor pins until it stops (you should hear a click).
- 🔌 Connect the wires to the terminals according to photo taken earlier.
- 🔌 Install the fixing bar or bracket.
- 🔌 Close the compressor protective casing.
After assembly, turn on the refrigerator. Normal operation is characterized by a smooth hum of the compressor and the absence of frequent clicks. After 10-15 minutes, check whether the evaporator inside the chamber has begun to cool.
Frequent errors in diagnostics and repairs
Many beginners make mistakes that can aggravate the situation. One of the most common is trying to clean the contacts with sandpaper. In modern relays, the contacts have a special coating, and its violation will lead to rapid burning and repeated failure.
The condition of the compressor itself is also often ignored. If the relay burns out, this could be due to the fact that the motor is difficult to spin (jamming, lack of freon). Installing a new relay on a faulty compressor will lead to instantaneous combustion of the new part.
Do not forget about safety. Even after disconnecting from the network, a charge may remain in the capacitors. Be careful when touching metal parts.
Is it possible to temporarily start a refrigerator without a relay?
Theoretically, it is possible by manually closing the contacts, but this is extremely dangerous and can lead to a fire or electric shock. This can only be done for a split second to check the motor by professionals.
Questions and answers (FAQ)
Is it possible to repair a burnt-out relay yourself?
In most cases, repairing a relay is impractical. The cost of a new part is low, and restoring the factory parameters of the coil or replacing a posistor at home is almost impossible without special equipment. It is easier and more reliable to buy a new unit.
Why does the relay click, but the refrigerator does not turn on?
The click means that the thermal relay or timer is trying to start the compressor, but the start relay does not work or the motor cannot turn over. This may be a sign of a malfunction of the relay itself, a break in the compressor windings, or mechanical jamming of the piston group.
How often do you need to change the relay in the refrigerator?
The service life of the relay is designed for the entire life of the refrigerator (10-15 years). However, power surges in the network can shorten this period. Scheduled replacement is not required, they are changed only when malfunctions occur.
Is a relay from one brand of refrigerator suitable for another?
Yes, if the technical characteristics match: type of compressor, power, voltage and type of fastening. Many manufacturers use compressors from the same factories (for example, Danfoss/Secop), so the relays can be interchangeable.