A sudden stop of the refrigerator often causes panic, because this threatens the spoilage of a large supply of food. In most cases, the cause of failure is not the compressor itself, but its “assistant” - starting relay. This small but critical element is responsible for starting the engine and protecting it from overloads. If you notice that the engine hums, clicks, but does not start, or turns on only for a split second, there is a high probability that the problem lies in this unit.
Before calling a technician or buying a new unit, it makes sense to conduct independent diagnostics. Understanding this how to check a relay on a refrigeratorcan save you a significant amount of money and time. In this article, we will analyze the structure of the mechanism, methods for checking it using a multimeter and visual inspection, and also point out subtleties that are often overlooked when repairing household appliances.
It is worth noting that working with electrical components requires compliance with safety measures. Any manipulations inside the unit are permissible only after completely disconnecting the device from the power supply. Ignoring this rule may result in electric shock or damage to the electronics of the refrigerator.
Design and principle of operation of the starting relay
For high-quality diagnostics, it is necessary to understand how the unit functions. The start relay is an electromagnetic switch that energizes the compressor start winding only when it starts. As soon as the motor rotor reaches the required speed, the relay opens the circuit and the motor continues to operate on the main winding. In parallel with the starting function, it often works thermal relay, opening the circuit when the current increases critically.
Structurally, the device consists of a coil, a movable core and a contact group. When the refrigerator is turned on, the current in the windings is high, the magnetic field draws in the core, closing the contacts of the starting winding. When the motor starts, the current drops and the core is pulled down by gravity or a spring, breaking the circuit. Violation of this cycle leads to characteristic clicks.
⚠️ Attention: Some models of Indesit and Ariston refrigerators use relays with a posistor. Their operating principle is different: there the role of a switch is played by a heating element, and not by a mechanical core. Testing such devices requires a different approach.
It is important to distinguish between relay types, since they are not always interchangeable. There are devices with a vertical and horizontal rod arrangement, as well as differences in the number of contacts. Installing the wrong component can result in instantaneous burnout of the compressor windings.
What are the dangers of using the wrong relay?
Using a relay with incorrect cut-off current characteristics can result in the starting winding remaining energized for too long. This causes its overheating and interturn short circuit, which actually means the need to replace an expensive compressor.
External signs of a relay malfunction
You can determine the breakdown even before disassembling the unit, paying attention to the behavior of the refrigerator. The most common symptom is the motor cycling on and off with a characteristic clicking sound. You may hear a buzzing sound that lasts 3-5 seconds, followed by a loud clicking sound and silence. After some time, the cycle repeats.
Another sign is the lack of cold in the chambers when the fan is running (if there is one) and the hot walls of the condenser, which do not have time to cool down. The compressor tries to start, but due to the lack of a starting impulse, the rotor cannot move. Thermal protection is triggered, preventing the engine from burning out, but also preventing it from working.
- 🔊 Characteristic clicks: a loud knock is heard immediately after switching on or during operation, followed by the engine stopping.
- 🔥 Overheating of the case: the back wall of the refrigerator in the area of the motor gets very hot, you can smell it burning or scorched plastic.
- 💡 Power surges: at the moment of starting the attempt, the light in the room may dim or knock out the circuit breakers in the panel.
If you observe such symptoms, the probability of failure of the trigger mechanism is more 80%. However, other problems should not be ruled out, such as jamming of the compressor itself or faulty wiring. An accurate diagnosis will be made only by checking the internals.
Preparation for diagnostics and safety measures
Before you start checking the relay, it is necessary to ensure safe working conditions. The refrigerator must be completely defrosted if ice has accumulated in the system, and unplugged for at least 2 hours. This is necessary to discharge the capacitors and cool the components.
To carry out the work, you will need a minimum set of tools. The main device will be multimeter (tester) capable of measuring resistance and checking the integrity of the circuit. You will also need a screwdriver to remove the protective cover of the compressor and, possibly, pliers to carefully remove the terminals.
☑️ Preparing to check the relay
Inspect the compressor for visible damage. If traces of oil are visible on the motor housing, this may indicate a leak in the seal, which is often accompanied by moisture getting on the relay contacts. In this case, simply replacing the relay may not solve the problem.
⚠️ Attention: Never touch the copper pipes and compressor housing immediately after operating the refrigerator. The temperature of heated elements can reach 70-80 degrees Celsius, which can cause burns. Allow the unit to cool naturally.
Visual inspection and dismantling of the relay
The diagnostic process begins with dismantling. Remove the cardboard or plastic cover from the back of the refrigerator that covers the compressor. The relay is usually placed directly on the compressor terminals and secured with a bracket or latches. Carefully disconnect it, after remembering or photographing the wiring diagram.
The first stage of testing is visual. Carefully inspect the relay housing for melting, blackening or swelling. If the plastic turns black, this is a sure sign of overheating and a short circuit inside. It is also worth shaking the relay near your ear: if you hear the sound of parts coming off inside, the device is definitely faulty.
Pay attention to the contacts. Oxidation or carbon deposits on the terminals may prevent current flow. In some cases, it is enough to clean the contacts with fine sandpaper to restore functionality, but if the deposit is deep, it is better to replace the relay.
If there are no external defects, we move on to a deeper check. Disassembling the relay itself (if its design allows this without destruction) can reveal burnt contacts inside. However, modern disposable housings often have to be carefully opened, which makes reassembly impossible.
Checking the relay with a multimeter
The most accurate diagnostic method is checking the electrical parameters with a multimeter. Switch the device to resistance (Ohm) or continuity measurement mode. First, check the integrity of the coil: the resistance should be within normal limits (usually from 30 to 200 Ohms, depending on the model). If the device shows one or infinity, the coil has burned out.
Then check the contacts. In the initial position (the relay lies horizontally or vertically, depending on the type), the contacts of the starting winding must be open. When voltage is applied (which at home is emulated by turning the relay over to check the operation of the core), they should close. The resistance between closed contacts should tend to zero.
For thermal relays, checking the bimetallic strip is important. It should open the circuit when heated. Ring the contacts of the thermal relay: in a cold state they should ring (resistance is close to 0 Ohm). If the circuit is open on a cold relay, it is faulty.
| Test type | Normal reading | Malfunction symptom | Action |
|---|---|---|---|
| Relay coil | 30 - 200 Ohm | Infinity (break) | Relay relay |
| Contacts (closed) | 0 - 2 Ohm | High resistance | Cleaning or replacement |
| Thermal relay (cold) | 0 Ohm (circuit) | Open circuit | Replacing the thermocouple |
| Posistor | 10 - 50 Ohm | Short circuit | Replacing the posistor |
Pay special attention to checking for “breakdown” to the housing. Press one multimeter probe to the metal body of the relay, the other to the contacts. The device should not show any resistance. The presence of conductivity indicates an insulation failure, which is life-threatening.
Specifics of checking a relay with a posistor
In modern refrigerators, such as LG, Samsung or Whirlpoolstart-protective devices with a posistor are often used. This is a semiconductor element that changes its resistance when heated. When cold, its resistance is low and it passes current to the starting winding. Heating up from the passing current, the posistor sharply increases the resistance, actually opening the circuit.
Checking the posistor with a multimeter is possible only in a cold state. The resistance should be in the range of 10-50 Ohms. However, even normal resistance does not guarantee serviceability, since the key parameter is the change in resistance when heated. It is difficult to check this at home, so if a fault is suspected, the posistor is changed preventively.
The main difference between such systems is the absence of moving mechanical parts. There is nothing to knock or stick here, but the posistor can “go wild” and not increase the resistance, leaving the starting winding energized, which leads to its burnout.
⚠️ Attention: After trying to start a refrigerator with a posistor, you must let it cool for at least 5-7 minutes before turning it on again. The posistor takes time to return to its original low resistance. Frequent switching on without a pause can lead to false diagnosis.
Replacement and final recommendations
If diagnostics confirm a malfunction, the relay must be replaced. You need to buy a strictly similar model. The part number is usually stamped on the body (for example, PTMRS 14 K or R6). Using universal relays is possible, but requires precise selection of the cut-off current and compressor type.
When installing a new relay, make sure that it sits tightly on the compressor terminals. Poor contact will cause sparking and repeated failure. After assembly, turn on the refrigerator and check the first cycle of operation: the start-up should be smooth, without long hums and clicks.
If the situation has not changed after replacing the relay, the problem probably lies deeper - in the compressor itself (an interturn short circuit or wedge) or in the wiring. In this case, you cannot do without the intervention of a specialist with professional equipment.
Is it possible to repair the relay yourself?
Theoretically, you can clean the contacts or bend the plate, but practice shows that such relays do not work for long. The cost of a new element is low, and the risk of burning the compressor if it breaks again is too great to save.
Regular maintenance, including cleaning the condenser from dust and checking the tightness of the seals, will help reduce the load on the starting system. Taking good care of equipment extends the service life of even the most complex components.
FAQ: Frequently asked questions
Is it possible to start a refrigerator without a relay?
Technically, you can start a compressor by applying voltage directly to the starting winding, but doing this is strictly prohibited in domestic conditions. Without a protective relay, the compressor will burn out in a few seconds or minutes due to the lack of overload protection. This is a temporary measure for diagnosis by a technician, and not a method of operation.
Why does the relay heat up during operation?
A little heating is acceptable, but if the relay body is so hot that it hurts to touch it, this is a sign of a malfunction. Possible reasons: incorrect selection of relay (wrong cut-off current), sticking contacts or problems with the compressor, which consumes increased current.
How to distinguish a relay failure from a compressor failure?
If the relay clicks, but the compressor is silent, most likely the problem is in the relay or the starting winding. If the relay turns on, the compressor hums for 5-10 seconds and turns off due to thermal protection - the compressor may become wedged. Only measuring the current consumption and winding resistance will give an accurate answer.
Where can I find the number of the relay to replace?
The marking is applied directly to the plastic or metal body of the device. To see it, the relay must be removed from the compressor. You need to look for a code that usually starts with letters (R, PTM, CSR) and numbers. It is better to show a photo of the marking to the seller of spare parts.