A sudden stop of the compressor or a characteristic click, after which the refrigerator goes silent, often indicates problems with the engine starting system. It is starting relay responsible for supplying a starting impulse to the motor winding, allowing it to overcome inertia and start working. If this small but critical element fails, the compressor hums but does not start, or the thermal protection is constantly triggered.
Diagnostics of this unit is one of the most accessible procedures in the repair of household appliances, which can be done independently with a minimum set of tools. Relay is an electromechanical a switch that closes the starting winding only at the moment of start, and then opens the circuit. Understanding the principle of its operation and the ability to check the starting one use the device with a multimeter will help save time and money when calling a technician.
In this article we will analyze in detail the algorithm of actions, consider typical symptoms of a breakdown and provide a table of resistance values for various models. It is critically important to completely disconnect the refrigerator from the power supply before starting any work, since we are talking about direct contact with high-voltage components. You should not ignore safety rules, because capacitors can retain a charge even after the device is turned off.
Symptoms of a faulty start relay
The first sign that starting relay requires attention is the unnatural behavior of the compressor when trying to start. Most often, the user hears a dull click, followed by a motor hum that lasts a few seconds, followed by another click and complete silence. This means that the engine is trying to start, but without the help of the relay it cannot develop the required speed, and protection comes into play, opening the circuit to prevent overheating. thermal relay protection by breaking the circuit to prevent overheating.
Sometimes the situation looks different: the refrigerator works, but the cycle switching on and off becomes too short. The compressor may only run for 10–20 seconds before shutting down for a few minutes. This mode of operation is extremely harmful to the motor windings and can lead to expensive repairs or replacement of the compressor itself. It is also worth paying attention to external signs: if you see blackening or melting of the relay housing, the diagnosis is obvious without additional diagnostics.
⚠️ Attention: If you hear a loud cracking sound during startup or see sparks in the compressor area, immediately stop trying to connect the device to the network. This may indicate a short circuit inside the starter or a breakdown of the insulation of the windings.
In some cases, the malfunction manifests itself in the fact that the refrigerator stops freezing, although the light inside is on and the fan (if there is one) is working. The compressor may be cold because it simply does not start. If you hear that the motor is humming, but does not start, and at the same time it is very hot to the touch, the problem may be not only in the relay, but also in the jamming of the compressor itself or a problem with starting winding.
Preparing for diagnostics and dismantling of the relay
Before you begin check the start relayit is necessary to ensure safe access to the node. Modern refrigerators, be it Indesit, Atlant or Bosch, have a similar design of the lower part where the compressor is located. To get started, you will need to remove the rear panel covering the engine compartment. It is usually attached to bolts or latches, which can be easily removed with a Phillips screwdriver.
After removing the panel, you will see a black cylindrical or pear-shaped compressor tank. There is a plastic box on the side or top of the motor housing - this is the device you are looking for. It can be mounted on a frame or simply put on the contacts. Before removal, it is recommended to photograph the position of the wires and the relay itself so that during assembly there is no confusion with the connection.
☑️ Preparation for diagnosing the relay
Remove the relay carefully, without using excessive force. It is often secured with a metal bracket or plastic clips. If the device has thermal protection, it can be built into the housing or connected with a separate wire. Carefully inspect the wires for melted insulation. If you find traces of burning or a burning smell, this is a sure sign that electric arc the contacts inside the relay have been destroyed.
Why does the relay overheat?
A frequent cause of overheating and subsequent failure of the starting relay is Unstable voltage in the network or frequent power surges. This can also be caused by wear of the compressor windings when the engine consumes an increased starting current that exceeds the design standards for the relay. In such cases, replacing only the relay gives a temporary effect, and after some time the situation repeats.
External inspection and initial assessment of condition
After removing the relay from its seat, a thorough visual inspection should be carried out. The device body must be intact, without cracks or traces of thermal effects. If the plastic is blackened or deformed, further inspection may not make sense - the element requires replacement. Inside the case there is a contact group and, in the case of electromagnetic relays, a coil with a core, and in posistor relays there is a ceramic element.
Shake the relay near your ear. If you hear a ringing or knocking sound inside, it may mean that internal components are broken or have become loose. Electromagnetic relays are characterized by a slight knocking sound of the moving core when tilted, but it should not be loud. For posistor relays (PTC), which are more often found in modern models, the integrity of the ceramic disc is important. Any chips or cracks on it make the device inoperable.
Pay special attention to the contacts. They must be clean, without soot, oxides or greenish deposits. Oxidation of the contacts increases the resistance in the circuit, which leads to a voltage drop on the starting winding and the inability to start the compressor. If the contacts are slightly dirty, they can be carefully cleaned with fine sandpaper, but if they are burnt or welded to each other, the relay must be disposed of.
⚠️ Attention: The technical characteristics of the relay (operation current, connection type) must strictly correspond to the markings on the compressor. Installing an unsuitable relay may burn out the motor starting winding. Always check the codes and parameters before purchasing a new part.
Checking with a multimeter: step-by-step algorithm
The most accurate way to check the starting relay is to use an electronic one. multimeter. Switch the device to the resistance measurement mode (Ohm), selecting the 200 Ohm limit or the continuity mode. First, check for an open circuit. Depending on the type of relay, the methodology may differ slightly, but the basic principles remain the same for all devices.
If you have a posistor relay in your hands (usually a small plastic cube), measure the resistance between the main contacts. In a cold state, a working posistor should show a resistance in the range of 10–50 Ohms (the exact value depends on the model). If the multimeter shows one (infinity), then an open circuit has occurred and the circuit will not close. If it shows zero, a short circuit is possible.
For electromagnetic relays (larger, often with a coil inside), the test is performed differently. It is necessary to “ring” the coil. The resistance of a working coil is usually several tens of ohms. It is also important to check the contacts that close during startup. At rest they can be open (the resistance is infinite), but when voltage is applied (which is difficult to check at home without a stand) they must close. The integrity of the thermal protection circuit is often checked if it is built into the relay - the resistance should be close to zero.
| Relay type | Normal resistance (Ohm) | Fault symptom | Action |
|---|---|---|---|
| Posistor (PTC) | 10 - 60 Ohm | Infinity or 0 Ohm | Replacement |
| Electromagnetic (coil) | 20 - 100 Ohm | Open circuit | Replacement |
| Thermal protection | 0 – 1 Ohm | Open circuit (cold) | Replacement |
| Switching contacts | 0 Ohm (closed) | High resistance | Cleaning or replacement |
In the diagnostic process, it is important not only to measure the resistance, but also to understand the logic of operation. Start relay - this is a disposable element in terms of response cycle life. Even if it “rings” but does not start the engine, its response characteristics may have changed. A posistor, for example, may show normal resistance, but not warm up to the required temperature in the required time, which is why it does not open the starting winding in time.
Typical errors during self-diagnosis
Many amateur craftsmen, trying check the starting relaymake mistakes that can lead to false conclusions. One of the most common is checking a relay that is not disconnected from the compressor. In this case, you measure the resistance of the entire circuit, including the motor windings, which gives distorted results. Always remove the relay from its seat before taking measurements.
Another mistake is ignoring the thermal protection state. Often users change the relay, leaving the old thermal protection, which has already lost its properties. As a result, the new element burns out after a few days or weeks of operation. Always check the protection circuit separately. It should ring short when cold.
It is also a mistake to assume that if a relay “rings”, it is fully operational. Mechanical wear of contacts leads to an increase in contact resistance. The multimeter may show the norm, but under load (with a starting current of 10–15 Amps), the contact will heat up and spark. Therefore, if the relay has been in service for more than 10 years, its preventive replacement is often more advisable than a risky inspection.
⚠️ Attention: Do not attempt to repair the relay housing by gluing or insulating tape if it is cracked. Sparking occurs inside, and sealing (or at least protection from dust and moisture) is important for safety. It is cheaper to buy a new original or high-quality analogue.
Replacement of the relay and final assembly
If the diagnostics showed a malfunction, it is necessary to replace it. Make sure that the new relay has identical markings or matches the electrical parameters (operation current, compressor type). Installation is carried out in the reverse order of removal. Securely snap the relay onto the compressor contacts until you hear a characteristic click.
Connect the wires according to the photograph taken earlier. Mixing up the start and run winding wires can cause the compressor to hum but not start, or the fuse in the relay will blow. After assembling all electrical connections, install a metal bracket or retainer, if provided by the design.
Before closing the back panel, you can conduct a test run. Plug in the refrigerator and listen. The launch should be confident, without a long hum. After a few seconds, the extraneous sounds should stop, leaving only the smooth hum of the operating compressor. If everything went well, secure the panel and watch the temperature rise for several hours.
Frequently asked questions (FAQ)
Is it possible to start a refrigerator without a start relay?
Theoretically, some craftsmen try to start the compressor directly by closing the contacts manually, but this is extremely dangerous and ineffective. Without a relay, the motor will not receive the necessary starting torque and will quickly burn out from overload. In addition, without a posistor or electromagnetic breaker, the starting winding will remain in the circuit, which will lead to its instantaneous combustion. It is strictly not recommended to do this.
Why does a new relay burn out a week after replacement?
If a new one starting relay fails so quickly, the reason lies not in it, but in related problems. Most often, this is a poor contact in the circuit (oxidized wires), a faulty thermal protection that does not turn off the motor when overheated, or, worst of all, a “dying” compressor with an interturn short circuit that consumes too much current.
What is the difference between a starting and running capacitor?
In refrigerators these concepts are often confused. A starting relay (often with a posistor) switches the windings. The capacitor (if it is in the circuit, usually in older models or specific compressors) creates a phase shift for the starting torque. Most modern household refrigerators use a circuit with a starting relay, and the capacitor may be absent or built into the control system.
Where can I find the markings for selecting an analogue?
The markings are applied to the plastic relay case itself (for example, R6, PTMRS, K-13B, etc.) and to the compressor nameplate. It is also important to know the power of the compressor (for example, 1/5 HP, 1/4 HP) and the type of refrigerant (R134a, R600a), since relays with different response currents are used for different refrigerants and capacities.