Sudden silence of the refrigerator or, conversely, its noisy operation without cooling often indicates problems with the heart of the unit - the compressor. It is this unit that is responsible for circulating the refrigerant, creating the necessary pressure in the system. When the equipment stops freezing, the first thing that comes to the owner’s mind is calling a technician, but initial diagnostics can be carried out independently, having a minimal set of tools at hand.
The most accessible and informative test method is measuring the electrical resistance of the motor windings. This procedure allows you to identify an open circuit, short circuit or breakdown to the housing, which in 80% of cases explains the failure of the device to start. Understanding the principle of operation of an electric motor and the ability to use a measuring device will save you from buying unnecessary spare parts or expensive but useless repairs.
Before taking active steps, you must completely turn off the power to the refrigerator. Unplug the power cord and gain access to the lower rear of the chassis. It is there, in the engine compartment, that compressor is located - a black metal barrel, to which copper tubes and an electrical cable are suitable. Accuracy and compliance with safety precautions play a decisive role here.
Preparation for diagnostics and safety precautions
Any work with electrical equipment requires strict adherence to electrical safety rules. Even if the refrigerator is unplugged, a residual charge may remain in the capacitors of the starting equipment. Before touching the contacts, make sure you are working in a dry area and your hands are not wet. To check, you will need a digital multimeter (tester), a set of screwdrivers and, possibly, pliers.
Remove the protective cover of the engine compartment. It is usually secured with latches or several screws. Inside you will see not only the compressor, but also a start-up relay, which is placed directly on the motor contact pins. To access the terminals of the relay windings, you must carefully dismantle it. It may be supported by spring clips or simply sit on the contacts, sometimes secured by a plastic frame.
⚠️ Warning: Never attempt to remove the start relay or touch the contacts while the power cord is plugged into the outlet. The risk of electric shock at this moment is maximum.
After removing the relay, three contact pins will open in front of you, forming a triangle. These are the conclusions of the windings starting, working i common wire. It is important not to confuse their purpose, although this is not critical for initial testing of circuit integrity. Visually inspect the contacts: there should be no traces of burning, oxidation or melting of the plastic. If obvious signs of thermal damage are visible, diagnostics may no longer be needed - the unit requires replacement.
Set the multimeter to resistance measurement mode (denoted as Ω), selecting a limit of 200 Ohm. Connect the probes to each other to make sure the device is working properly and see the zero value (or wire resistance value). Now you can start taking measurements directly at the motor terminals.
☑️ Preparation for testing
Identification of pins and connection diagram
The three pins on the compressor are not randomly located, they form an isosceles triangle. The top of this triangle is always general conclusion (Common). The other two pins, located at the base of the imaginary triangle, are the outputs of the starting and operating windings. To understand which is which, you need to take a series of resistance measurements between all three pairs of contacts.
Take a multimeter and measure the resistance between each pair of pins. Write down the three values you get. The logic here is simple: the sum of the resistances of the two smaller values should be equal to the largest value (taking into account the instrument error). The highest measured resistance is the resistance between the starting and working terminals.
The remaining two measurements will show the resistance of the starting and working windings relative to the common wire. Typically, the starting winding has a higher resistance (since it is wound with a thinner wire), and the working winding has a lower resistance. For example, if you get the values 30 ohms, 15 ohms and 45 ohms, then 45 ohms is the sum (between start and run). Therefore, 30 Ohms is the starting winding, 15 Ohms is the working winding, and the common terminal is located between them.
Color marking of relay wires
In some relay models, the wires to the windings are color-coded. The red wire usually goes to the starting winding, white or blue to the working winding, and black to the common one. However, you cannot rely only on color, since manufacturers can change standards.
Knowing the resistance of a working engine, you can immediately eliminate some of the faults. For household refrigerators, the operating winding resistance is considered normal in the range of 10–20 Ohms, and the starting winding resistance is 20–40 Ohms. The exact numbers depend on the power of the motor and the model compressor, but the order of the values is always preserved.
Checking for open circuits and short circuits
The most common reason why the refrigerator hums, but does not start, or is silent is an open circuit inside windings When testing, the multimeter should show a specific numerical value of resistance. If the unit in the leftmost digit (or the infinity symbol OL) lights up on the display, this means that the circuit is broken.
A break can occur in any of the windings. If the resistance is infinitely high between the common terminal and the working one, it means that the working winding has burned out. If between general and starting - accordingly, starting. In both cases the compressor will not work. It is almost impossible to restore a break inside a sealed casing; replacement of the unit is required.
The opposite situation is a short circuit. In this case, the resistance will tend to zero. However, an interturn short circuit is more dangerous, when the insulation between the turns of the wire is broken. In this case, the resistance drops below normal, but not to zero. A motor with an interturn short circuit can hum, jerk and quickly overheat, knocking out the thermal protection relay.
⚠️ Attention: If the resistance of one of the windings differs significantly from the passport data (for example, 2-3 Ohms instead of 15), this is a sure sign of an interturn short circuit. It is dangerous to operate such a compressor - it can completely burn out within a few minutes of operation.
For accurate diagnostics, a comparison with reference values for a specific model is sometimes required. Below is a table of typical resistance values for popular types of compressors.
| Compressor type | Working winding resistance (Ohm) | Starting winding resistance (Ohm) | Total resistance (Ohm) |
|---|---|---|---|
| Atlant (single-phase) | 12 – 18 | 25 – 35 | 37 – 53 |
| LG / Samsung | 10 – 15 | 20 – 30 | 30 – 45 |
| Danfoss (Secop) | 15 – 22 | 30 – 45 | 45 – 67 |
| Embraco | 11 – 16 | 22 – 32 | 33 – 48 |
Diagnostics of breakdown on the housing
A separate and extremely important type of test is diagnosis of breakdown of the insulation of the windings on the compressor housing. This is a situation where phase voltage can reach the metal casing of the motor. If the refrigerator is standing on the floor without grounding, this can lead to an electric shock when touching the case or even a fire.
To check, switch the multimeter to the continuity mode (where there is a speaker symbol) or resistance measurement to the maximum limit (2 MOhm and higher). Press one probe tightly to any clean metal place on the compressor body (you can lightly clean the paint with a knife or file for better contact), and with the second one touch all three contacts on the block in turn.
The device should be silent, and the screen should display a resistance tending to infinity. If you hear a squeak or see any resistance readings (even hundreds of kOhms), this means the insulation has failed. It is strictly forbidden to operate such a compressor, as it becomes deadly.
Hidden defects: interturn short circuit
The most insidious fault, which is difficult to detect with a conventional multimeter, is a slight interturn short circuit. The resistance may differ from the norm by only a few ohms, which is within the limits of measurement error or difference in copper temperature. However, when voltage is applied, such a motor begins to consume increased current.
An indirect sign of an interturn short circuit can be the behavior of a thermal relay. If the compressor starts, runs for 1-3 minutes, gets very hot and clicks when it turns off, this is a sign of overcurrent. This may also be indicated by humming and vibration without shaft rotation (if there is no jamming of the mechanics).
For accurate diagnostics at home, you can use the method of measuring current consumption. To do this you will need current clamps. When starting, a working compressor briefly consumes a high starting current, which then drops to the operating value (usually 0.5 - 1.0 A for household models). If the current immediately increases to 2-3 A and grows further until the protection is triggered, there is an interturn short circuit or wedge.
There is also an “old-fashioned” method of testing through an incandescent lamp, but it is less accurate and requires caution. The essence of the method is to connect a compressor in series with a powerful lamp (100-150 W). If there is a turn short, the brightness of the lamp will be much higher than usual, and the motor itself will hum.
Frequent errors during testing and their consequences
Beginners often make mistakes that lead to false diagnoses. One of the most common is checking without removing the start relay. In some designs, the relay blocks access to the pins, and trying to measure resistance through the relay contacts gives an incorrect result, since you are measuring the resistance of the internal elements of the relay, not the windings.
Another mistake is dirty or oxidized multimeter probes. If oxide deposits have formed at the ends of the probes, contact with the leads will be poor and the device will show a break or huge resistance. Always clean the contacts before measuring and press the probes tightly.
It is also worth remembering that some modern inverter compressors have a motor design that may differ from the classic three-phase or single-phase circuit. In such cases, standard testing of the three terminals may not be informative, since the control is carried out by complex electronics, and the windings may have a different connection.
⚠️ Attention: Technical specifications and connection diagrams may vary depending on the manufacturer and year of manufacture of the model. Before replacing the compressor, check the technical documentation for the specific refrigerator model.
If after all the checks it turns out that the windings are intact, there is no breakdown in the housing, and the refrigerator does not work, the problem may lie in the start relay, thermostat or control unit. However, the serviceability of the windings is the foundation, without which further diagnostics make no sense.
FAQ: Frequently Asked Questions
Is it possible to replace one compressor winding?
No, it is impossible. The windings are located inside a sealed steel casing, filled with oil and soldered. Rewinding a refrigerator motor is not economically feasible and technically difficult. If there is a break or short circuit, the entire compressor assembly changes.
Why does the multimeter show zero between all contacts?
This is a sign of a serious short circuit inside the motor, most likely melting of the insulation and collapse of the turns of both windings. Also check that the measuring range on the device is selected correctly. If the range is correct, then the compressor must be disposed of.
How to distinguish the starting winding from the working winding without a circuit?
The starting winding always has greater resistance, since it is wound with a thinner wire. The working winding has less resistance and is made of thicker wire to allow the main current to pass. By measuring all three pairs of contacts, you will calculate the resistance of each winding relative to the common terminal.
The compressor is humming, the windings are intact, what is the reason?
If the electrical part is working properly (there are no breaks or short circuits), but the compressor is humming and does not start, a mechanical wedge of the piston group is likely. Also, the cause may be a malfunction of the starting relay, which does not give a short-term impulse to the starting winding.
Is it dangerous to check the compressor under voltage?
Yes, it is life-threatening. The resistance test is carried out only with the device completely de-energized. Testing of operation under voltage (to measure current) should only be carried out by a qualified specialist in compliance with all safety precautions.