The situation when the refrigerator stops freezing, and only a quiet hum or periodic clicks are heard from the back, is familiar to many owners of household appliances. Most often, the cause of such a malfunction is the failure of the compressor electric motor, which is the heart of the entire cooling system. Before purchasing an expensive new part or calling a technician, it makes sense to conduct an initial diagnosis to understand whether the problem really lies in the motor.
To conduct a quality check, you will need a basic set of tools and, of course, multimeter. This device allows you to measure the resistance of an electrical circuit and determine the integrity of the conductors inside the engine. If you are faced with the fact that the compressor does not start, the thermal relay hums and turns off, or traces of melting are visible on the housing, checking the windings will be the first logical step in troubleshooting.
In this article we will analyze in detail the algorithm of actions that will allow you to determine the condition of the engine with a high degree of probability. We will look at how to distinguish between types of windings, which instrument readings are considered normal, and which will indicate irreparable damage. Correct diagnostics will save you time and money, allowing you to make an informed decision on further actions.
The operating principle and design of electric motor windings
To successfully carry out diagnostics, you need to understand how the structure asynchronous motoris installed inside the sealed compressor casing. Typically, such motors have two main working windings: starting and working. They are wound with copper wire and located in the stator, creating the necessary magnetic field to rotate the rotor. Understanding the difference between them is critical for correctly interpreting the tester readings.
The working winding is designed to maintain shaft rotation in normal mode and has a thicker wire, which means less electrical resistance. The starting winding, on the contrary, is made of thinner wire and has high resistance. It comes into operation only at the moment the engine starts, helping to overcome the inertia of rest, after which the starting relay is turned off.
⚠️ Attention: All work on checking the compressor should be carried out exclusively with the power supply disconnected from the network. A voltage of 220 volts is dangerous to life, and the presence of capacitors in the circuit can retain charge even after being unplugged from the outlet.
In some models of modern refrigerators, especially inverter type, the motor design may differ, but the principle of the presence of windings remains basic. However, the classic circuit with a starting and operating circuit is found in the vast majority of household models of brands Indesit, Atlant, Beko i Liebherr. It is with their example that we will consider the testing methodology.
There should be no electrical connection between the windings and the metal body of the motor. The insulation of the wires must be perfect, since any breakdown on the body will trigger the protection or cause an electric shock when touching the body of the refrigerator. Checking for a ground fault is a mandatory diagnostic step, along with measuring the resistance of the coils themselves.
Necessary tools and preparation for diagnostics
You do not need complex industrial equipment to carry out measurements. The main tool will be a digital multimeter, which can be purchased at any electrical goods store. Make sure that the device is working properly, the battery is charged, and the probes have intact insulation. You will also need a set of screwdrivers to remove the compressor protective casing and, possibly, pliers.
Before starting work, you must ensure safe access to the engine contact group. To do this, unplug the refrigerator, move it away from the wall and remove the rear metal or plastic panel at the bottom of the unit. Under it you will see a black cylindrical or pear-shaped element - this is compressor, to the end of which a plastic box with a starting relay is attached.
- 🔧 Digital multimeter with the function of continuity and resistance measurement (Ohm).
- 🔧 A set of screwdrivers (phillips and flat) for dismantling panels.
- 🔧 Pliers for careful removal of wires and terminals.
- 🔧 Electrical tape or marking tags for identifying wires.
- 🔧 Dry rags for cleaning contacts from dust and oxides.
It is important to thoroughly clean the contact group from dust, oil and possible carbon deposits before measurements. Oxidized contacts may give false high resistance readings, leading to misdiagnosis. If black carbon deposits are visible on the contacts, they should be carefully cleaned with fine sandpaper or a file.
After removing the start relay, three terminals coming out of the motor housing will open in front of you. They can be arranged in a triangle or in a row. It is to these contacts that we will connect the multimeter probes. Before removing the relay, it is recommended to photograph the connection diagram or mark the wires so as not to mix up the contacts during assembly, although this is not as critical for diagnosing the windings as for the final assembly.
The process of removing the starting relay and access to the contacts
The starting relay is a small plastic block placed on the contacts of the compressor. It is responsible for supplying voltage to the starting winding at the moment of start and its subsequent shutdown. It must be removed carefully, as the plastic latches become brittle over time. In some models, the relay is fixed with a metal bracket-bar, which must be bent or unscrewed.
After dismantling the bracket or latches, the relay is carefully removed from the contacts, slightly rocking from side to side. Do not use excessive force to avoid damaging the ceramic insulation of the terminals or the contact group itself. Inside the relay you will find a starting capacitor and a switching mechanism, but to check the windings, it is important for us to have access to the three pins on the motor body.
⚠️ Attention: When removing the relay, pay attention to the condition of the contacts inside it. If they turn black or melt, this may indicate poor contact, which often causes overheating and subsequent failure of the windings.
The contacts on the compressor itself are usually located in a triangle. The top contact is often common, and the bottom two are winding leads. However, the exact diagram depends on the engine model. On some compressors, markings are applied directly on the case next to the terminals: C (Common) - common, R (Run) - working winding, S (Start) - starting winding.
☑️ Checking readiness for measurements
If The markings are erased or missing; the purpose of the contacts can only be determined by measurements, which will be discussed in the next section. The main safety rule is to never measure resistance while mains voltage is applied to the contacts.
Methodology for measuring winding resistance
First, put the multimeter in resistance measurement mode (Ohm), selecting the limit of 200 or 2000 Ohms. First you need to find the common wire. To do this, we call pairs of contacts one by one. The probes are applied to any two terminals, and the reading is recorded. Then the probes are swapped to another pair. The pair of contacts that shows the least resistance corresponds to the terminals of the working and starting windings, and the remaining third contact will be common.
Next, we measure the resistance between the common contact and each of the other two. The resistance between the common contact and the output of the working winding should be minimal (usually in the range of 10–30 Ohms). The resistance between the common contact and the start winding terminal will be higher (usually 30–60 ohms). The sum of these two values should equal the resistance measured directly between the terminals of the starting and operating windings.
What to do if the readings “float”?
If the numbers on the multimeter screen are constantly changing or slowly increasing, this may indicate the presence of moisture inside the windings or poor contact of the probes. Try cleaning the contacts and warming up the compressor with a hairdryer (without overheating!) to remove moisture. If instability persists, the wire insulation may be damaged.
It is important to understand that the exact resistance values depend on the engine power and model of the refrigerator. For low-power compressors, the resistance can reach 40-50 Ohms, for powerful ones it can be about 10-15 Ohms. The key here is the ratio: the working winding always has less resistance than the starting winding.
After measuring the resistance between the terminals, it is necessary to check that there is no breakdown to the housing. One multimeter probe is applied to any of the three contacts, and the second is applied to a cleaned area on the compressor housing (where there is no paint). The device should show infinity (one in the most significant digit or an overload symbol). Any other value indicates insulation breakdown.
Interpretation of results and fault table
The received data requires correct decoding. The condition is considered normal when the resistance of the windings corresponds to their type, and there is no breakdown to the housing. However, there are often deviations that clearly indicate a malfunction. Below is a table that helps classify the condition of the engine according to the instrument readings.
| Multimeter readings | Diagnosis | Probability of repair | Actions |
|---|---|---|---|
| Resistance in normal, no breakdown | Engine is OK (electrically) | High | Check relay, thermostat, wiring |
| Infinity between terminals | Open windings | Zero | Replacement of the compressor |
| Close to zero resistance | Interturn short circuit | Zero | Replacement of the compressor |
| There is resistance to the housing | Insulation breakdown on the housing | Zero | Replacement of the compressor (dangerous!) |
The most common and a dangerous defect is interturn short circuit. In this case, the winding resistance will be significantly lower than normal, and when you try to start, the compressor will hum and quickly heat up, knocking out the circuit breaker. It can be difficult to determine an interturn short circuit only with a multimeter if it is not strong, but a clear underestimation of the resistance is a sure sign.
A broken winding is easily determined: the device shows infinity where there should be resistance. This means that the wire inside has burnt out or has moved away from the contact. It is impossible to restore a sealed compressor at home, since this requires opening the casing, resoldering the windings and again sealing the system while maintaining a vacuum.
It is also worth mentioning the so-called “sticking” of the rotor. If the motor is electrically working (the resistance is normal, there is no breakdown), but when voltage is applied it does not spin, but only hums, the mechanical unit may be jammed. This cannot be checked with a multimeter; specialized testing is required.
Typical diagnostic errors and expert advice
One of the common mistakes is ignoring the condition of the multimeter probes. If the ends of the probes are oxidized or the wires inside are broken, the readings will be incorrect. Always check the device itself by connecting the probes to each other: it should show zero or a value close to it (wire resistance).
Another mistake is trying to measure resistance “on weight” without ensuring reliable contact. The contacts on the compressor may be coated with an oxide film. Easy stripping and tight pressure of the probes are required. Also, you should not take measurements immediately after the refrigerator is running: a hot motor has a different resistance than a cold one due to the temperature coefficient of copper.
- 🔍 Do not confuse insulation resistance and winding resistance. These are different parameters.
- 🔍 When measuring, do not touch the metal parts of the probes with your hands so as not to introduce an error.
- 🔍 If you doubt the readings, compare them with the data of a working compressor of the same series.
It is worth considering that some modern models use engines with additional leads for temperature sensors or built-in protection. In such cases, there may be more than three contacts. Before checking, be sure to find technical documentation (diagram) for a specific compressor model, for example Secop or Embraco.
If you find that the windings “ring” normally, but the refrigerator does not work, the problem may lie not in the engine, but in the control system. In this case, it is worth checking the start relay, thermostat and the integrity of the supply wires. Often a burnt out relay simulates the symptoms of a faulty motor.
FAQ: Frequently Asked Questions
Is it possible to check the compressor without removing it from the refrigerator?
Yes, you can. Simply remove the back panel and the start relay housing. However, for convenience and safety of measurements, it is better to move the unit and provide good access to the rear wall. There is no need to remove the compressor itself from the frame.
What resistance is considered normal for a household refrigerator?
The normal range for the operating winding is 10–30 Ohms, for the starting winding – 20–60 Ohms. The exact value depends on the motor power. The main thing is that the starting winding has a resistance greater than the working winding, and there is no breakdown on the housing.
What to do if the resistance of the windings is normal, but the compressor does not start?
Most likely, the starting relay or thermal protector is faulty. A mechanical compressor wedge is also possible. Try replacing the relay with a known good one. If this does not help, a mechanical defect is likely.
Is it dangerous to check a running compressor?
It is strictly forbidden to measure the resistance of a live motor with a multimeter in the "Ohm" mode - you will burn the device. Resistance testing is carried out only on completely de-energized equipment.
Is it possible to restore a burnt winding?
In a home workshop - no. Rewinding requires removing the casing, which breaks the tightness of the system. After this, evacuation and refilling with freon will be required, which is only possible with specialized equipment.