A sudden stop of the compressor and silence in the kitchen space are often the first signals of a malfunction of the refrigeration unit. If you notice that the engine hums but does not start, or clicks and immediately goes silent, most likely the problem lies in the engine starting system. Start relay is a compact but critical element that supplies the starting impulse to the compressor winding. Without its correct operation, the refrigerator turns into a useless box for storing food.
Before calling a technician or buying a new part, it makes sense to carry out initial diagnostics yourself. To do this, you will need a minimum set of tools, the main one of which is multimeter. This device allows you to accurately measure electrical resistance and circuit continuity, which gives an unambiguous answer to the condition of the component. In this article, we will analyze in detail the algorithm of actions that will help you with a high degree of probability determine whether the relay is working or it’s time to replace it.
It is worth noting that working with electrical appliances requires compliance with basic safety rules, which we will definitely mention. However, the process of contact testing itself does not pose a high danger if the refrigerator is first disconnected from the network. Diagnostics takes only a few minutes, but allows you to save a significant amount on calling a specialist if you decide to replace it yourself.
Design and principle of operation of the starting relay
To effectively carry out the test, you need to understand exactly how this node functions. The start relay is an electromechanical switch that closes the compressor start winding circuit only when it starts. As soon as the motor rotor reaches the required speed, the relay opens the contacts, and the motor continues to operate on the main winding. In modern models, most often there are devices with a posistor, where the role of a switch is played by a temperature-sensitive element.
Structurally, the device consists of a housing, a contact group and a coil (or posistor). When voltage is applied, current flows through the coil, creating a magnetic field that draws in the core and closes the contacts. If the system uses posistor, then when current passes it heats up, its resistance increases sharply, and the starting winding circuit is broken. Understanding this mechanism is important for interpreting multimeter readings.
The malfunction may lie in sticking contacts, burnt-out coils, or destruction of the posistor. It is not always possible to determine this visually, especially if there are no obvious traces of burning or melting on the body. That is why checking with a multimeter is the only reliable way to assess the condition of internal components without disassembling the compressor itself.
⚠️ Attention: Residues of freon or oil may remain inside the relay if the device is tightly connected to the system. When dismantling, avoid sudden movements and do not damage the copper tubes of the compressor, as this will require complex recharging of the system.
Relay types
electromagnetic and posistor: In older models of refrigerators, such as some series Atlant or Biryusa, electromagnetic relays with a vertical arrangement were often installed. They are noisier in operation. Modern units, including most models Indesit and LG, are equipped with posistor starters, which are considered more reliable and quiet, although the principle of checking them with a multimeter remains similar.
Preparation for diagnostics and safety measures
Any work with electrical components of household appliances begins with completely de-energizing the device. Unplug the power cord and make sure there is no obstruction to the back of the refrigerator. You will need free space to maneuver and good lighting of the work area. Also prepare a clean rag, since dust and technical grease often accumulate in the compressor niche.
To carry out high-quality diagnostics, you will need a digital multimeter set to resistance measurement mode (usually designated as Ω or 200 Ohm). Additionally, you may need pliers, a screwdriver, and possibly contact cleaner if you plan to service them. Make sure that the multimeter probes are in good condition and the wires do not have insulation damage.
It is also important to let the compressor cool down if it has been running recently. Hot metal can cause burns, and residual heat can affect the posistor readings during testing. If the relay just clicked, wait 10-15 minutes before starting. This time is also necessary for the pressure in the refrigerant system to equalize.
- 🔌 Completely disconnect the refrigerator from the power supply and wait for the capacitors to discharge.
- 🧤 Wear protective gloves to avoid getting your hands dirty with oil or getting hurt by metal burrs.
- 🔦 Provide bright lighting, since contact markings are often small and difficult to see in the shadows.
- 🛠️ Prepare a container to drain possible condensate or oil from the relay casing.
Removing the start relay from the compressor
The process of removing the relay may differ slightly depending on the manufacturer of the refrigerator, but the general algorithm is the same. First you need to gain access to the compressor, located at the lower rear of the unit. Remove the protective cardboard or metal panel, if present. You will see a view of a black cylindrical motor-compressor, to which a bundle of wires fits.
On the side or top of the compressor there is a plastic box - this is our desired relay. It is put directly on the three terminals of the compressor. In some models, for example, in refrigerators Stinol or Candy, the relay can be additionally secured with a metal bracket or a plastic clip. Carefully remove the retainer, being careful not to damage the plastic fastening ears.
It is not necessary to disconnect the wires from the relay itself at this stage if the length of the cables allows it to be removed from the compressor terminals. However, for a more accurate and convenient check, it is better to disconnect the terminals. Remember or mark with a marker which wire is connected where. Usually the wires are color-coded, but you shouldn’t rely on that alone, as the colors may have faded over the years of use.
⚠️ Attention: The compressor leads (plugs) are very fragile. When removing the relay, proceed carefully, loosening it from side to side, rather than yanking it upward. Incorrect movement can break the ceramic base of the terminals, which will lead to expensive repairs or replacement of the compressor.
☑️ Safe dismantling algorithm
External inspection and search for visible defects
Before handling the multimeter, conduct a thorough visual inspection of the removed device. Often the nature of the malfunction is obvious without measuring instruments. Shake the relay near your ear: if you hear a distinct knocking or ringing inside, it means the mechanical part is damaged or the core has come off. In good condition, the inside should be quiet or only a slight noise of the posistor can be heard.
Carefully inspect the internal cavity and contacts. The presence of black carbon deposits, melted plastic or traces of sparking indicates that the contacts are burnt and do not provide a proper connection. If you see cracks on the posistor body or it crumbles when touched, then the part definitely requires replacement. Such defects often arise due to power surges in the network.
Pay special attention to the condition of the springs and moving elements in electromagnetic relays. The spring should not be stretched or broken, and the movable core should move freely inside the coil. If the mechanism is stuck, the relay will not be able to perform its starting function. In such cases, even normal resistance readings do not guarantee the dynamic performance of the unit.
| Visual sign | Probable cause | Action |
|---|---|---|
| Black deposits on contacts | Sparking, poor contact | Cleaning or replacement |
| Cracks on the posistor body | Thermal destruction | Replacement only |
| Knock when shaking | Destruction of internal elements | Replacing the relay |
| Melted plastic | Overheating, short circuit | Replacing the relay and checking the wiring |
Step-by-step check with a multimeter: resistance and integrity
Now We move on to the most important stage - instrumental diagnostics. Switch the multimeter to resistance measurement mode (200 Ohm or 2 kOhm limit). If you have an electromagnetic relay, you need to ring the coil. Connect the probes to the coil contacts: the device should show a certain resistance, usually in the range from 20 to 60 Ohms, depending on the model. If the multimeter shows one (infinity) or zero, the coil is faulty.
For posistor relays the procedure is slightly different. A posistor in a cold state should have a low resistance, usually from 3 to 50 Ohms. Connect the multimeter probes to its terminals. If the resistance is normal, this does not guarantee 100% serviceability, since the posistor may lose its properties when heated. However, an open circuit (infinite resistance) or a short circuit (0 Ohm) indicates a definitive breakdown.
It is also necessary to check the contacts for short circuits among themselves when the relay is in the open state. The probes are connected to different pairs of contacts. The device should not show resistance (there should be one on the screen). If the multimeter beeps or shows low resistance where it should not be, it means that the contacts are “stuck” or the dielectric is broken.
⚠️ Attention: Technical characteristics of resistances may differ between different compressor manufacturers (for example, Secop, Embraco, GMCC). If you doubt the readings, find the technical documentation specifically for your refrigerator model to check the reference values.
- ⚙️ Set the multimeter to the
Ω(Ohm) mode to a limit of 200 Ohms. - 🔌 Check the integrity of the coil or posistor winding (there must be resistance).
- 🚫 Make sure there is no short circuit between the contacts (there should be one/open).
- 🔄 If necessary, check the mobility of the contacts in the dynamics (for electromagnetic relays).
Interpretation of results and common errors
Having received the readings of the device, it is important to decipher them correctly. If the multimeter shows "1" at the 200 ohm limit when testing a coil or posistor, this means an open circuit. The part is dead and cannot be restored. If the device shows “0” or a value close to zero where there should be resistance, this indicates a short circuit of the turns, which also requires replacement.
A common mistake for beginners is to ignore the condition of the wires going to the relay. Sometimes the relay itself is working properly, but the copper wire at the point of connection to the terminal has rotted. Be sure to feel the wires along their entire length and clean the contacts before final assembly. Copper oxidation can create additional resistance, which the multimeter may not notice, but which will prevent the powerful compressor from starting.
Another nuance: checking "by weight". Some types of relays only operate in a certain spatial position (usually pointing up). If you test an electromagnetic relay by holding it sideways, the contacts may not close due to gravity, and you will mistakenly assume that the relay is faulty. Always consider the orientation of the device when testing.
Can the relay be repaired?
Theoretically, an electromagnetic relay can be disassembled, the contacts can be cleaned with fine sandpaper and put back together. However, the seal of the housing will be compromised, which will lead to oxidation in the future. PTC relays are non-separable monoblocks. Considering the low cost of a new part, repairing an old relay is not economically feasible and less reliable.
FAQ: Frequently asked questions
Is it possible to start a refrigerator without a starting relay?
Technically, you can start a compressor by applying voltage directly to the starting winding through a button, but this requires qualification. It is strictly forbidden to operate a refrigerator without a relay: the engine will not be able to reach operating mode, will overheat and burn out in a few minutes due to operation only on the starting winding.
Why does a new relay burn out after a week?
This may indicate problems with the compressor itself (turn-to-turn short circuit of the windings), power surges in the network or incorrect selection of analogue. Make sure that the new relay has exactly the same characteristics (current, type, orientation) as the original one.
How to distinguish a starting relay from a thermal one?
Often they are combined in one housing. The starting one is responsible for the start (breaks the starting winding circuit), and the thermal (protective) one opens the entire power circuit in case of overheating or overcurrent. In modern refrigerators, this is most often a single unit that changes entirely.
Where can I find the markings for selecting a replacement?
The required numbers and letters are printed on the plastic body of the relay itself. This is usually the manufacturer's code (for example, PTC, R6) and the catalog number. You can also search by compressor model, information about which is on the sticker on its case.
Is it dangerous to change the relay yourself?
If you follow electrical safety rules (disconnect from the mains) and carefully handle the compressor terminals, the risk is minimal. The main thing is not to damage the copper tubes and connect the wires correctly according to the diagram.