A sudden stop in the operation of a refrigeration unit is often accompanied by silence, which is more frightening than a constant hum. If you hear that the motor is humming, the relay is clicking, but the cold does not appear, or the unit is silent, the first thing to do is to suspect a malfunction compressor. It is this unit that is the heart of the system, ensuring the circulation of the refrigerant.
Before calling a technician or buying new equipment, 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 will allow you to determine the integrity of the engine's electrical circuits and identify obvious defects in the windings without disassembling the complex hydraulic system.
However, it is worth understanding that an electrical test is only part of the diagnosis. Mechanical failure of the piston group or loss of compression is not always visible on the tester, but the absence of resistance or a short to the housing will immediately indicate the need to replace the unit. In this article, we will analyze in detail the algorithm of actions that will help you make the right decision about repairs. wedge piston group or loss of compression is not always visible on the tester, but the absence of resistance or a short to the housing will immediately indicate the need to replace the unit. In this article we will analyze in detail the algorithm of actions that will help you make the right decision about repairs.
Safety precautions and preparation for diagnostics
Working with electrical appliances connected to a 220 Volt network is always associated with the risk of electric shock. Even if the refrigerator appears to be turned off, there may still be a charge in the capacitors, and careless handling of live wires is dangerous. Therefore, the first rule is complete decontamination equipment before starting any manipulations.
You need not just turn off the refrigerator with the button, but also physically remove the plug from the socket. Only after this can you begin to dismantle the rear protective panel to gain access to the motor. If you plan to ring contacts during startup (which is rare and requires experience), make sure your hands are dry and your shoes have non-conductive soles.
⚠️ Warning: It is strictly forbidden to touch exposed contacts or compressor terminals while the power cord is plugged into the outlet. The risk of receiving an electric shock when checking live circuits is extremely high.
To conduct high-quality diagnostics, you will need a digital or dial multimeter capable of measuring resistance in the range from 0 to 20 kOhm. Also, pliers, a screwdriver and electrical tape will not be superfluous. Before starting work, wipe the compressor housing with a dry rag, removing any dust that may affect the accuracy of measurements when checking for breakdown.
Electric motor design and winding diagram
To correctly interpret the readings of the device, you need to understand how the asynchronous motor refrigerator works. Inside the sealed casing are the stator and rotor. There are two main windings wound on the stator: starting and working. They have different resistance and number of turns, which allows you to create torque.
The starting winding usually has a higher resistance and is made of thinner wire, since it only works at the moment of starting. The working winding, on the contrary, is designed for long-term operation and has less resistance. The third contact is generalthrough which current flows to both windings. Understanding this logic is critical for correct diagnosis.
The compressor terminal block typically has three terminals, which may be labeled with letters or symbols. Depending on the manufacturer (Atlant, Indesit, LG), the marking may differ, but the physical principle remains the same. If the markings are erased, the contacts can only be determined by measuring the resistance between them.
Below is a table showing typical resistance values for various types of compressors. Please note that the numbers may vary depending on the power and model of the engine.
| Winding type | Resistance (Ohm) | Characteristics | Wire color (often) |
|---|---|---|---|
| Operating | 10 - 25 Ohm | Less resistance | Red/White |
| Starting | 25 - 50 Ohm | Higher resistance | Blue/Black |
| Total sum | Sum R1+R2 | Integrity check | - |
| Case | Infinity | Dielectric | Green/Yellow |
Why are the resistances different?
The difference in resistance is due to the thickness of the wire and the number of turns. The starting winding must create a strong magnetic flux to move the rotor from its place, so it has more turns and thinner wire, which gives more resistance.
The process of taking readings with a multimeter
The testing procedure begins with a visual inspection of the terminal block. Make sure that the contacts are not oxidized or have any traces of carbon deposits. If there is rust on the contacts, sand them with fine sandpaper to a metallic shine, as the oxide film can distort the measurement results.
Switch the multimeter to the resistance measurement mode (usually indicated as Ω) at the 2 kOhm or 20 kOhm limit. Connect the probes to each other - the device should show zero or one (depending on the type of device), which will confirm the serviceability of the tester itself and the probes. Now you can start taking measurements on the compressor.
Apply the probes sequentially to pairs of contacts. You need to get three values: between the first and second, second and third, first and third pins. Write down the numbers you get. The sum of the resistances of the two smaller values must be equal to the largest value. This is the basic law Kirchhoff for this circuit.
☑️ Algorithm for checking the windings
If you received values, for example, 20 Ohms, 40 Ohms and 60 Ohms, then the circuit is intact. If the device shows one (infinity) on some segment, it means in this winding break. If it shows zero, a short circuit of the turns has occurred.
Pay special attention to the cleanliness of the probe contacts. Dirty or oxidized probes can produce an error of several ohms, which can be confusing when diagnosing low-power windings. Wipe them before the final measurement.
Checking for insulation breakdown (housing)
The most dangerous defect in the electrical part of the compressor is the breakdown of winding insulation on the metal body. In this case, the phase gets on the refrigerator casing, which creates a real threat to human life when touching the device. It is imperative to check this parameter.
For diagnostics, set the multimeter to the maximum resistance measurement limit (200 kOhm or 2 MOhm). Press one probe tightly to any of the three contacts on the terminal block, and the second to a place on the compressor housing that has been cleared of paint (you can use a tube fitting or a grounding bolt).
The device should show infinity (one in the most significant digit). If you see any numbers, even large ones (for example, 50 kOhm), this indicates a violation of the dielectric properties of the insulation. Operating such a refrigerator is prohibited without grounding and installing an RCD, and ideally, the compressor requires replacement.
⚠️ Attention: The presence of resistance between the winding and the housing, even 10-50 kOhm, indicates the beginning of insulation destruction. Over time, this parameter will deteriorate until a complete breakdown occurs.
Sometimes a breakdown appears only when the engine heats up. In a cold state, the insulation can hold, but during operation, when the copper expands, contact appears. Therefore, if the refrigerator knocks out the machine after some time of operation, checking with a multimeter in a cold state may not show anything, but the suspicion of a breakdown remains.
Analysis of results and typical faults
Having received the numbers, you need to interpret them correctly. A condition is considered normal when the resistances fall within the ranges specified in the technical documentation or the table above, and the sum of the two smaller ones is equal to the third. Any deviation requires analysis.
Interturn short circuit is an insidious defect in which the winding resistance drops below normal. The engine may hum, the hum will be louder than usual, and the current consumption will increase. The multimeter will show a value significantly less than expected (for example, 2-5 ohms instead of 15). In this case, the compressor often burns out completely in a short time.
If the device shows a break (infinity) on the starting winding, the refrigerator will not start, only a click of the relay will be heard. If there is a break in the working winding, the motor is silent. In both cases, replacement of the unit or rewinding is required (which is not economically feasible in modern conditions).
It is also worth considering the influence of temperature. Copper resistance depends on temperature: the hotter the motor, the higher the resistance. Therefore, it is better to carry out measurements on a cold compressor that has been standing for several hours.
Mechanical causes of failure with working electrics
There are situations when the multimeter shows ideal resistance values, the insulation is intact, but the refrigerator does not work. This indicates mechanical or a hydraulic problem. The engine is electrically functional, but cannot perform its function.
The most common reason is a wedge of the piston group. The motor tries to start, it hums, the relay clicks, trying to give a starting impulse, but the shaft does not turn. After a few seconds, the thermal relay opens the circuit and there is silence. Attempts to “revive” such a compressor by applying voltage are directly dangerous and rarely give long-term results.
The second reason is loss of compression. The valves inside the compressor could burn out or break. The motor spins and hums, but does not create the necessary pressure for freon circulation. In this case, the outlet tubes will be barely warm, but there will be no cold in the evaporator. It is difficult to check this without a pressure gauge station, but you can indirectly look at the sound: a compressor operating without load hums differently, more “lightly.”
The third reason is a clogged capillary tube or a freon leak. In these cases, the compressor itself may be absolutely fine, but the system does not work. Diagnostics of these components requires other equipment and skills that go beyond a simple test with a multimeter.
⚠️ Attention: If, after replacing the start relay and checking the windings, the compressor hums but does not start, do not try to forcefully rotate the shaft or knock on the housing. This can lead to depressurization of the casing and the release of oil.
Frequently asked questions (FAQ)
Is it possible to check the compressor without removing it from the refrigerator?
Yes, an electrical test (winding resistance and breakdown to the housing) can be performed without removing the compressor. Simply remove the back cover and gain access to the terminal box. However, to check the pressure or mechanical wedge, the compressor often has to be dismantled.
What to do if the resistance of the starting and operating windings is the same?
In asynchronous refrigerator motors, the resistances of the starting and operating windings are almost never the same. If the device shows equal values, most likely the motor has a specific circuit (rare) or, more likely, one of the windings has an interturn short circuit that has changed its parameters. Replacement is required.
Why does the multimeter show "1" when checking the windings?
The number "1" in the most significant digit on digital multimeters means infinity (open circuit). This indicates that there is a wire break inside the winding. It is impossible to restore such a winding at home; the compressor must be disposed of or replaced.
Does the oil inside the compressor affect the multimeter readings?
Motor oil is a dielectric and does not conduct current. Therefore, the presence of oil on the terminal block contacts should not affect winding resistance measurements unless it is mixed with metal shavings or dirt that creates a conductive bridge. It is better to wipe the contacts with alcohol before taking measurements.