The refrigerator has stopped freezing, and the compressor is silent or humming, but does not start? In most cases, the problem lies in the electrical part of the motor. Independent compressor diagnostics allows you to save a significant amount on calling a technician and understand exactly whether the unit can be repaired or requires a complete replacement. The main tool for such a check is a conventional digital multimeter.
Before grabbing the tools, you need to understand that compressor is the heart of the refrigerator, and its failure is often associated with external factors, such as power surges or wear of the start relay. Checking the integrity of the stator windings is the first and most important stage of troubleshooting. If the multimeter shows an open or short circuit, further operation of the device is impossible without intervention in the electrical circuit.
To carry out the work, you will need not only a measuring device, but also basic skills in working with electrical equipment. In this article we will look in detail at how to correctly measure the resistance between the terminalsdetermine the type of fault and interpret the obtained values on the tester display.
Preparation for diagnostics and safety measures
Any work with electrical appliances begins with ensuring your own safety. The first step should always be to completely unplug the refrigerator. Unplug from the socket and make sure that the rear of the unit is freely accessible. Often, to access the compressor, you need to move the refrigerator away from the wall and remove the bottom protective panel or casing.
After gaining access to the motor, you need to remove the start-up relay. It is under this plastic block that there are three contacts coming from the motor windings. To remove the relay, pliers or a simple screwdriver are usually enough, but you need to be careful not to damage the fragile plastic latches or wires. Before disconnecting the wires, it is recommended to photograph the connection diagram so as not to mix up the contacts during assembly.
⚠️ Attention: Before starting measurements, be sure to discharge the capacitor (if there is one in the circuit) and make sure that there is no residual voltage at the motor terminals. Also check the integrity of the multimeter probes - damaged wire insulation can lead to electric shock if the device is accidentally turned on in the future.
Visual inspection of the compressor can also provide a lot of information. If you see melted plastic, blackened wires or smell burning, then the probability of electrical breakdown inside the windings approaches 100%. In such cases, testing with a multimeter is more of a confirmatory nature, but it is still necessary to carry it out for the final verdict.
Compressor design and winding diagram
To correctly interpret the multimeter readings, you need to understand that there are two main electrical circuits inside the motor: the start winding and the (working) winding. They are wound on the stator and have different resistances. The third contact is common. Understanding this structure is critical for correct diagnosis.
Usually the starting winding is made of thinner wire and has a larger number of turns, so it is electrical resistance always higher than that of the working winding. The working winding is wound with a thicker wire and is designed to maintain rotor rotation after start. The difference in resistance is a key marker of engine health.
On the compressor terminal block, the contacts may be located differently, but their markings are standardized. The following designations are most often used:
- 🔌 C (Common) - common contact.
- 🚀 S (Start) - starting winding (has greater resistance).
- ⚙️ R (Run) - working winding (has less resistance).
In some models, especially old Soviet or specific ones brands like Atlant or Birius, the markings may differ or be applied to a metal tag next to the terminals. If there are no markings, you will have to determine the contacts empirically, measuring the resistance between all pairs of terminals.
Setting up the multimeter and the dialing process
For diagnostics, we will need a resistance measurement mode, indicated on the device as Ω (Ohm). If your multimeter does not have autoranging, set the limit to 2 kΩ (2000 Ω). Before starting measurements, connect the probes to each other: the device should show zero or one in the last digit, which will confirm the serviceability of the probes.
The testing process consists of three main stages. First, we measure the resistance between the common contact and the terminal of the working winding. Then - between the common contact and the starting winding. And finally, we check the resistance between the starting and working windings directly. The sum of the first two measurements should be approximately equal to the third measurement.
Measurement results must be compared with reference values. For most household refrigerators, the compressor power is in the range of 100-200 W, which corresponds to certain resistance values. Below is a table of approximate values for different types of engines.
| Compressor type | Starting winding resistance (Ohm) | Working winding resistance (Ohm) | Total resistance (Ohm) |
|---|---|---|---|
| Low power (up to 100 W) | 40 - 60 | 15 - 25 | 55 - 85 |
| Medium power (120-150 W) | 25 - 35 | 10 - 18 | 35 - 53 |
| Powerful (more than 200 W) | 15 - 25 | 6 - 12 | 21 - 37 |
| Inverter (BLDC) | Depends on models | Depends on the model | Requires special. diagnostics |
It is important to understand that the readings may differ slightly depending on the temperature of the engine. Cold engine will show less resistance than a warm one. Therefore, if the refrigerator has just been running, let it cool for at least 30 minutes before checking.
☑️ Checklist for checking with a multimeter
Analysis of results: normal, open and shorted
Having received the numbers on the screen, you need to be able to read them correctly. If the multimeter shows one in the most significant digit (for example, 1 or OL), this means infinite resistance. In the context of checking windings, this is a signal about open circuit. The wire inside the winding has burned out and no current flows through it. Such an engine cannot be repaired.
If the device shows a value close to zero (for example, 0.0 or 0.5 Ohm), this indicates a short circuit of the turns. In this case, the resistance drops critically low, which, when connected to the network, will cause instant burning of the wiring or knocking out plugs. An interturn short circuit is often accompanied by a characteristic hum and an attempt by the shaft to turn, but there is not enough power to start.
A separate case is a “floating” fault. It happens that when the engine is cold, the continuity test shows normal, but when it heats up to 50-60 degrees, the resistance increases sharply or drops to zero. This occurs due to expansion of the metal and loss of contact inside the winding. It is difficult to identify such a defect with a regular test; you need a heat chamber or a hair dryer for local heating.
⚠️ Attention: Do not confuse a short circuit of the windings with a working thermal protection relay. The thermal relay in good condition should “ring” (show 0 Ohm), and in emergency condition it should show a break. Check it separately, disconnecting it from the general circuit.
It is also worth paying attention to the stability of the readings. If the numbers on the multimeter display jump randomly, the contacts on the terminal block may be oxidized or the contact inside the probe itself may be broken. Clean the contacts with fine sandpaper and repeat the measurement.
Checking for insulation breakdown (housing)
The most dangerous type of malfunction is a breakdown of winding insulation on the metal body of the compressor. In this case, the phase gets on the body of the refrigerator, and when touching the metal, a person may receive an electric shock. You can only check this with a multimeter, but it is better to use a megohmmeter if you have one.
To check with a regular tester, switch it to the maximum sensitivity mode (usually 200 kOhm or 2 MOhm). Press one probe to a cleaned area on the copper tube or metal compressor housing (where there is no paint or rust), and with the second one touch all three contacts on the terminal block in turn.
In a working engine, the resistance between the housing and any of the contacts should be infinite (one in the most significant digit). If the device shows at least some value, even 50-100 kOhm, this indicates an insulation failure. Operating such a refrigerator is strictly prohibited without grounding and installing an RCD, but it would be more correct to replace the unit.
Specifics of inverter compressors
Modern refrigerators are increasingly equipped with inverter compressors that operate on the principle of frequency conversion. Their design differs from classic linear models. In such motors, the windings often have three phases, and there is no starting relay as a class.
The inverter motor continuity test LG, Samsung or Hitachi has its own characteristics. The resistance between any two contacts out of three must be the same. If you see a spread of values, for example, 10 Ohms, 10 Ohms and 5 Ohms, then one of the windings has a defect. Usually the resistance there is very low, in the range of 4-15 Ohms.
The main difficulty in diagnosing inverters is that they are controlled by a complex electronic module. Even if the windings are intact, the compressor may not start due to a failure in the control board. Therefore, for inverter models, testing with a multimeter provides only 50% of information about the health of the system.
⚠️ Attention: Inverter compressors are sensitive to static electricity. When working with their contacts, do not touch the terminals with your hands and use antistatic gloves, if possible, so as not to damage the sensitive electronics inside the motor.
If after testing it turns out that the windings are intact, but the refrigerator does not work, the problem may lie in the control module or temperature sensors. In this case, simply replacing the compressor will not solve the problem, but will only lead to new costs.
Frequent diagnostic errors
Beginners often make mistakes that lead to incorrect conclusions. One of the most common is trying to measure resistance without disconnecting the compressor from the control board. The presence of parallel circuits in the electronics of the refrigerator will distort the multimeter readings, and you may get a false resistance value.
Another mistake is ignoring the state of the probes. Dirty or oxidized probe ends create additional contact resistance. Always test the meter with a known resistance or by shorting the probes before making an important measurement. An error of 1-2 Ohms can be critical for low-power windings.
Also, do not forget about the temperature coefficient. As already mentioned, the resistance of copper increases with heating. If you just tried to start the refrigerator and it hummed, the windings may have become hot. Allow the equipment to cool to room temperature to obtain correct data.
Sometimes users confuse the start relay with the compressor itself. If the relay is faulty (the contacts are burnt or the rod is jammed), the compressor may be absolutely fine. Therefore, always start diagnostics by checking the relay and only then proceed to checking the motor.
Questions and answers (FAQ)
Is it possible to check the compressor without a multimeter?
It is impossible to accurately determine the condition of the windings without a measuring device. You can only indirectly judge by the signs: if, when turned on, the machine knocks out or the fuse burns out, there is probably a short circuit. If the motor hums and hums, but does not start, the starting winding may be broken or jammed. But for an accurate diagnosis you need a tester.
What is the normal resistance for the Atlant refrigerator compressor?
For most models Atlant with motors of the SKN or SKND series, the resistance of the working winding is 12-18 Ohms, and the starting winding is 25-35 Ohms. The exact values depend on the specific modification and year of manufacture.
What to do if the multimeter shows 0 Ohm between the contacts?
This is a sign of a short circuit of the turns. Such a compressor will not work; it will immediately trip the circuit breaker or burn out. Engine replacement required. Sometimes 0 Ohm may indicate a faulty multimeter itself or poor contact of the probes, check the device at another object.
Is it possible to revive a compressor with a breakdown in the housing?
In domestic conditions, it is impossible to restore broken winding insulation. Attempting to fill the engine with varnish or epoxy will not give a long-lasting result, since there is high pressure and temperature inside. Such a unit is dangerous to life and must be disposed of.
Why does the compressor ring but does not start?
If the windings are intact, but the motor is silent or humming, the reason may be a jammed mechanical part (piston group), a malfunction of the start relay, condenser, or lack of refrigerant in the system. Also, the thermal protector inside the motor could have worked due to overheating.