A sudden stop of the refrigerator often causes panic, but in most cases the cause of the breakdown is the electrical part of the motor-compressor. Before calling a technician or buying a new unit, it is worth conducting an initial diagnosis, which can save significant money. The main component that requires checking is the compressor winding, since it is this that ensures the rotation of the shaft and the compression of the refrigerant.
To carry out an accurate diagnosis, you will need a minimum set of tools, the main one of which is a multimeter. Understanding the principle of operation single-phase asynchronous motor will help you not only measure the numbers on the device screen, but also correctly interpret the data received. In this article we will analyze in detail the process of troubleshooting in the electrical circuit of the motor.
It is worth immediately noting that any work related to electricity and internal components of the refrigerator requires strict adherence to safety precautions. Improper handling of the tool or ignoring the rules can lead to electric shock or permanent failure of the equipment. If you are not confident in your abilities, it is better to entrust the repair to professionals.
Preparation for diagnostics and safety measures
The first and most critical step before starting any work is to completely disconnect the refrigerator from the electrical network. Remove the plug from the socket and make sure that the rear of the unit is freely accessible. For ease of operation, it is best to move the refrigerator away from the wall, providing good access to the compressor, which is usually located in the lower niche.
You will need to remove the protective casing (if any) and remove the start relay to gain access to the compressor contacts. Usually, this requires carefully pressing the latches or unscrewing the screws holding the plastic relay housing. After removing the relay, you will see three leads sticking out of the motor housing in the shape of a triangle.
⚠️ Warning: Before touching any metal parts, make sure that there is no charge left in the capacitor (if there is one in the circuit), although this is rare in modern household models. Work only with dry hands and use a tool with insulated handles.
To test, you will need a digital multimeter set to resistance measurement mode (Ohms). If you have a pointer instrument, it must be calibrated before use. It would also be a good idea to prepare insulating tape and a marker to mark the contacts if their markings have been erased.
☑️ Preparation for testing
Determining the type of windings and connection diagram
Before starting measurements, it is necessary to understand exactly what conclusions we are dealing with. Most household refrigerators use compressors with three contacts: two of them belong to the working and starting stator windings, and the third is common. Correctly determining the purpose of each pin is the key to successful diagnosis.
The contacts are usually located at the end of the compressor and can be marked with letters or numbers. Depending on the manufacturer (for example, Atlant, Indesit or LG), the labeling may differ. The most common designations are C (Common), S (Start) and R (Run). Sometimes numbers 1, 2, 3 are used instead of letters.
It is impossible to visually determine which output is responsible for what without dialing. However, knowing the typical layout helps you navigate faster. The working winding always has less resistance and is made of a thicker wire, while the starting winding has a higher resistance and is wound with a thinner wire to create a starting torque.
If the markings on the case are erased or missing, you will have to use the elimination method, measuring the resistance between all pairs of contacts. This is a standard procedure for older models, where the factory designations may have disappeared over time.
Features of inverter-type compressors
Inverter compressors have a different wiring diagram and often do not have a classic starting relay. Checking their windings requires specific knowledge and equipment, since they are controlled by complex electronics. The standard method of testing three contacts here may not give a complete picture of the engine's performance.
The process of testing windings with a multimeter
The process of measuring resistance itself is quite simple, but requires care. Set the multimeter switch to the 2 kOhm position (or 200 Ohm, depending on the model of the device). Touch any two contacts with the probes and write down the value obtained. Then repeat the procedure for other pairs of contacts.
You need to get three resistance values: between the first and second contacts, between the second and third, and between the first and third. The sum of the two smaller values must equal the largest value. This is the fundamental law of physics for this circuit: resistance between the starting and working windings equal to the sum of their resistances relative to the common wire.
For example, if between contacts A and B the resistance is 20 Ohms, between B and C - 50 Ohms, and between A and C - 70 ohms, then pin B is common. In this case, a winding with a resistance of 20 Ohms (between A and B) will be working, and with a resistance of 50 Ohms (between B and C) it will be starting. The total sum (20 + 50 = 70) confirms the correctness of the measurements.
It is important to carry out measurements carefully, without touching the metal parts of the probes with your fingers, since the resistance of the human body can distort the readings of the device, especially at high measurement limits. Hold the probes only by the insulated handles.
Analysis of the results obtained and table of values
After taking measurements, it is necessary to analyze the obtained figures. Normal resistance values depend on the power of the compressor and the model of the refrigerator. For household units, the resistance of the working winding is usually from 10 to 30 Ohms, and the starting winding is from 20 to 50 Ohms.
Below is a table with approximate values for popular types of compressors. Remember that small deviations are acceptable, but a critical discrepancy indicates a problem.
| Compressor type | Work winding (Ohm) | Start winding (Ohm) | Total (Ohm) |
|---|---|---|---|
| Low power (up to 100 W) | 25 – 35 | 40 – 55 | 65 – 90 |
| Medium power (100-150 W) | 15 – 25 | 30 – 45 | 45 – 70 |
| Powerful (more than 150 W) | 10 – 18 | 20 – 35 | 30 – 53 |
| No Frost compressors | 12 – 22 | 25 – 40 | 37 – 62 |
If the device shows one (infinity) in any of the sections, this indicates an open circuit. In this case, no current flows and the compressor will not work. Most often, the starting winding breaks due to overheating or a power surge.
If the multimeter shows zero or values close to zero, a short circuit of the turns can be diagnosed. This is a dangerous situation, since when turned on, such a compressor will consume a huge current and can burn out in a few seconds or knock out the automatic fuse in the panel.
Searching for a breakdown on the housing (short to ground)
One of the most dangerous faults is a breakdown of winding insulation on the compressor housing. In this case, an electrical potential appears on the metal body of the unit, which creates a direct threat to human life upon contact. It is imperative to check for breakdown.
To do this, switch the multimeter to the resistance measurement mode at the maximum limit (usually 2 MOhm or 20 MOhm). Press one probe to the cleaned area on the compressor body (where there is no paint or rust), and with the second touch each of the three contacts in turn.
If the insulation is working properly, the device should show infinity (one in the most significant digit). If you see any resistance values, even very large ones (such as several megaohms), this is a sign of deteriorating insulation. Ideally, no current should flow between the winding and the housing at all.
⚠️ Attention: If a breakdown is detected in the housing, operating the refrigerator is strictly prohibited! This may result in electric shock. Immediate replacement of the compressor or professional repair with rewinding is required (which is practically not done in domestic conditions).
Often a breakdown occurs at the point where the wires exit the motor housing, where the insulation is exposed to the greatest thermal impact. A visual inspection of this area sometimes helps to detect blackening or melting of the insulation.
Typical faults and their symptoms
Understanding the symptoms helps to quickly determine the nature of the breakdown. If the compressor hums but does not start, and after a while the thermal relay clicks, this is a classic sign of a stuck mechanical part or a problem with the starting winding. In this case, there is current in the working winding, but there is not enough torque.
The complete absence of sound when the refrigerator is plugged in may indicate an open circuit in the windings or a malfunction of the thermostat. If the light in the refrigerator is on, it means that voltage is coming to the unit, and the problem lies inside the motor or the starting relay.
An interturn short circuit often manifests itself in the fact that the compressor starts, runs very loudly, gets very hot and is quickly turned off by the thermal relay. In this case, the resistance of the windings will be lower than the nominal one, which causes increased current consumption.
Do not forget about the external factor. Sometimes a “faulty” compressor turns out to be completely healthy, and the problem lies in oxidized contacts in the start relay connector. Cleaning the contacts with fine sandpaper can bring the refrigerator back to life without replacing expensive components.
Frequently asked questions (FAQ)
Is it possible to start a compressor without a starting relay?
Technically, you can start the motor by applying voltage directly to the working and starting windings, but do this manually dangerous and ineffective. Without a relay, the starting winding will not turn off after starting, which will lead to its rapid combustion. There are special start buttons, but they are designed for short-term diagnostics, and not for permanent operation.
What to do if the resistance of the windings is normal, but the refrigerator does not work?
If the electrical part is intact, the problem may be mechanical (jamming of the piston group) or a malfunction of the starting relay, which does not supply an impulse to the starting winding. It is also worth checking the thermostat and the defrosting circuit.
Is it possible to rewind a burnt-out compressor yourself?
At home, it is almost impossible to rewind a refrigerator compressor. This requires special equipment for winding, pressing and vacuuming. In addition, the quality of such rewinding will be low. It is more economically profitable and reliable to buy a new compressor.
Why does the compressor housing heat up during operation?
Heating to 60-80 degrees Celsius is the norm for operating compressors. However, if the case is hot to such an extent that it is impossible to hold your hand, or it turns off after a couple of minutes of operation, this is a sign of an overload, an interturn short circuit or problems with the cooling system of the motor itself.