A sudden stop in the refrigerator is always stressful, because food supplies are at risk. Often the cause of the breakdown is compressor, which is the heart of the entire cooling system. Before calling a technician or buying new equipment, it makes sense to carry out an initial diagnosis to understand whether the game is worth the candle.
Checking the motor using multimeter allows you to identify an open circuit, short circuit or breakdown in the housing without complex equipment. This procedure requires minimal skills in handling electrical appliances and takes no more than 20 minutes. If you are ready to act carefully, you can independently determine the technical condition of the unit.
In this article we will analyze a step-by-step algorithm of actions that will help you understand whether your “motor” is alive or it’s time to change it. It is important to understand that an electrical test is only part of the diagnosis, but it provides 80% of the information about the condition of the electric motor.
Safety precautions and preparation for diagnostics
The first and most important rule is the total loss of power device. No manipulations inside the electrical circuit can be carried out while the cord is plugged into the outlet. Even briefly touching live contacts can cause serious injury or damage to the meter.
You will need access to the rear of the refrigerator. Usually the compressor is located in the lower niche, closed with a metal or plastic cover. To work you will need a Phillips screwdriver, pliers and, in fact, yourself multimeter. Make sure that the battery in the tester is charged, otherwise the readings will be incorrect.
⚠️ Attention: Before starting work, be sure to wait until the compressor has completely cooled down if it has been running recently. Hot windings may have altered resistance, and the risk of burning your hands on the metal casing is too great.
After removing the protective cover, you will see a black barrel with outgoing tubes and an electrical block. It is the terminals on this block that interest us. Carefully disconnect the connector coming from the relay and thermostat to gain free access to the motor contacts.
Visual inspection and search for external defects
Before taking up the tools, conduct a thorough visual inspection. Often the cause of the malfunction is visible to the naked eye. Pay attention to the condition of the wires: they should not be melted, broken or have signs of exposure to rodents. The insulation must be intact along its entire length.
Inspect the compressor housing itself. If you see traces of oil, especially around the tube fittings or in the lower part of the crankcase, this may indicate mechanical damage or depressurization. Oil smudges often accompany problems with the piston group, but can also be a result of vibration.
Check the condition of the starting and protective relay They are attached directly to the compressor terminals. If traces of burning, soot, or the smell of burnt plastic are visible on the plastic housing of the relay, this is a sure sign of a problem in the electrical circuit. However, a burnt relay does not always mean the death of the motor.
- 🔍 Look for blackened contacts on the connectors.
- 🔍 Check the integrity of the insulation of the supply wires.
- 🔍 Assess the presence of corrosion on metal elements.
- 🔍 Listen: if you hear a buzzing sound when you turn it on, but there is no startup, the problem may be jammed.
If there is no external damage, proceed to instrumental diagnostics. The absence of visible defects does not yet guarantee serviceability, since the windings can burn out inside the sealed casing.
Checking the integrity of the windings with a multimeter
Now we move on to the most important part - measurement resistance. There are usually three contacts on the compressor block: common (C or R), starting winding (S) and running winding (R or M). The location of the contacts depends on the model, but the principle of continuity is the same for all.
Switch the multimeter to the resistance measurement mode (Ohm), selecting the limit of 200 Ohm or 2 kOhm. First check each winding separately. Press one probe to the common contact, and the second to the contact of the starting winding. Record your readings. Then repeat the procedure for the working winding.
The normal resistance of the starting winding is usually higher than the working winding, and ranges from 20 to 50 Ohms. The work winding has a lower resistance, often in the range of 10-20 ohms. The exact values depend on the power of the engine and the model of the refrigerator.
Why are the resistances different?
The starting winding is made of thinner wire and has more turns to create the required starting torque. The working winding is designed for long-term operation and has less resistance to reduce heat losses.
If the device shows one (infinity) on any of the measurements, it means that there is an accident in the winding break. In this case, the compressor will not start, and it can only be restored by replacement. If the resistance is close to zero, this indicates an interturn short circuit.
After measuring individual windings, it is necessary to check the resistance between the starting and operating contacts. The sum of these readings should approximately equal the resistance measured between the two points directly. Any strong deviations indicate a violation of the structure of the coils.
Diagnostics of breakdown on the housing
One of the most dangerous types of malfunction is breakdown of the insulation of the windings on the housing. In this case, voltage may appear on the metal casing of the refrigerator, which creates a real threat to people's lives. It is imperative to check this condition.
Switch the multimeter to the dial mode (where there is a speaker icon) or resistance measurement to the maximum limit (2 MOhm and higher). Press one probe to any of the three contacts on the compressor block, and the second to a cleaned place on the metal body of the motor (for example, to a copper tube or fastening bolt).
If the device is silent or shows infinite resistance, the insulation is intact. If you hear a squeak or see resistance values in kilo-ohms and below, it means that something has happened Break on the body. It is strictly prohibited to operate such a refrigerator.
| Measurement type | Normal reading | Failure sign | Probable cause |
|---|---|---|---|
| Working winding | 10 - 25 Ohm | Infinity or 0 Ohm | Open or shorted turns |
| Starting winding | 20 - 50 Ohm | Infinity or 0 Ohm | Open or shorted turns |
| Breakdown to the body | Infinity (∞) | Any numbers or squeak | Insulation destruction, moisture |
| Interwinding | Sum R1+R2 | Significant difference | Insulation degradation between coils |
It is important to carry out this check for all three contacts in turn. Sometimes a breakdown may occur only on one of the windings, but this is enough to consider the motor faulty.
Analysis of the starting relay and thermal protection
Often the compressor itself is working, but does not start due to the failure of the attachments. The starting relay is responsible for short-term voltage supply to the starting winding, and thermal protection turns off the motor if it overheats. These elements can also be checked with a multimeter.
Remove the relay from the compressor contacts. Usually it is fixed with a bracket or simply sits tightly on the terminals. Carefully separate the parts. If the relay has a posistor (black cylinder inside), its resistance in the cold state should be low, but when heated it should increase sharply.
Thermal protection in the normal state should “ring” short (resistance is close to 0 Ohm). If the circuit is broken, it means that the protection has burned out or has worked and has not returned to its original position. In some cases, light tapping may return the contacts, but it is better to replace the element.
⚠️ Attention: Do not try to turn on the compressor bypassing the relay and protection to check for spark. This can lead to jamming of the piston group or final combustion of the windings due to lack of starting torque.
Check the contacts of the relay itself for the presence of carbon deposits. If they are blackened, the resistance at the point of contact will be high, which will prevent the motor from starting. Cleaning the contacts helps temporarily, but it is better to install a new set of relays.
Interpretation of results and further actions
After all measurements have been carried out, it is necessary to compare the data obtained. If the windings ring, there is no breakdown in the housing, and the relay is working properly, but the refrigerator does not work, the problem may be in the electronic control module or wiring. In this case, diagnostics become more complicated.
If measurements show a break, short circuit or breakdown, the compressor requires replacement. Repairing sealed units at home is impossible, since welding of pipes, evacuation of the system and refilling with freon are required.
It is also worth considering the age of the equipment. If the refrigerator is more than 10-12 years old, replacing the compressor may not be economically feasible. The cost of a new motor and the work to install it is often more than half the price of a new refrigerator.
In a situation where you doubt your conclusions, it is better to consult a specialist. Misdiagnosis can lead to the purchase of unnecessary parts. Remember that multimeter gives accurate numbers, but they need to be interpreted taking into account the overall picture.
Frequent errors when checking
Beginners often make common mistakes that lead to false conclusions. One of the most common is checking resistance on a hot engine. As mentioned earlier, temperature affects the resistance of copper, and the readings may differ from the passport data.
Another error is poor contact of the probes with the terminals. Oxidized contacts on the compressor block can produce high resistance, which the user mistakes for an open circuit. Always clean the contacts before measurements.
Also, do not ignore the condition of the multimeter itself. A dead battery or broken probes may show “infinity” where the circuit is intact. Test the device on a known good circuit (for example, a length of wire) before starting work.
- 🚫 Do not carry out measurements under voltage.
- 🚫 Do not ignore external signs (smell, color of wires).
- 🚫 Do not draw conclusions based on buzzing alone motor.
- 🚫 Do not forget to calibrate the device before starting.
Accuracy and attentiveness are the main tools of the master. Following these simple rules will save you from mistakes and help you accurately determine the cause of the breakdown.
☑️ Ready for testing
⚠️ Attention: Technical characteristics of compressors from different manufacturers may vary. The data in the article are averaged. For an accurate diagnosis, check the technical documentation for the specific model of your refrigerator.
Questions and answers (FAQ)
Is it possible to replace the compressor yourself without a vacuum sealer?
Theoretically, you can start the system without evacuation by blowing it with freon, but the service life of such a refrigerator will be extremely short. The remaining moisture and air in the system will lead to blockage of the capillary and combustion of the new motor. Professional refilling is required.
Why does the multimeter show different resistance values?
The spread of readings may be associated with the temperature of the windings, the quality of the contact of the probes, or the error of the device itself. Also, the resistance depends on the engine power: the more powerful the motor, the lower the resistance of the windings.
What to do if there is no breakdown, but the refrigerator does not turn on?
You should check the circuit to the compressor: thermostat, defroster, control module. Perhaps the voltage simply does not reach the motor. It is also worth checking the starting relay, even if visually it is intact.
Is it dangerous to touch the compressor during operation?
Yes, it is dangerous. In addition to the risk of electric shock if the insulation breaks down, the compressor gets very hot (up to 90-100°C). Touching may cause burns. All resistance checks are carried out only on a completely cooled and de-energized unit.
Can a new compressor burn out immediately after installation?
Yes, if the system has not been properly prepared (vacuuming, flushing from combustion products of the old motor) or if the starting relay is incorrectly selected. Also, the cause may be a power surge in the network.