How to determine the starting and operating windings of a refrigerator compressor

Repair of refrigeration equipment often begins with diagnosing the compressor, which is the heart of the entire system. In situations where the engine hums but does not start, or is completely silent when power is applied, the technician is faced with the task of checking the electrical circuit. Often the reason lies in an interturn short circuit or break, but for an accurate diagnosis it is necessary to clearly understand how the stator winding is structured and how to connect to it.

In this article we will analyze the physical principle of operation of asynchronous motors used in household appliances and learn how to determine the purpose of the terminals without factory documentation. Knowledge of winding resistance is a key skill that allows you to distinguish a serviceable motor from a burnt one, and also correctly connect a new compressor to replace the failed one. We will look at measurement methods with a multimeter and analyze typical values ​​for different manufacturers.

Before starting measurements, you need to understand that any single-phase refrigerator motor has two main windings located in the stator slots. The first is working winding, which consumes the main energy during operation, the second is the starting one, which is turned on only at the moment the rotor starts. It is the correct identification of these contacts that allows you to avoid fatal errors when assembling the circuit.

Principle of operation and design of windings

The electric motor of a household refrigerator is an asynchronous unit with a squirrel-cage rotor. To start the rotation of the shaft, the creation of a rotating magnetic field is required, which cannot be achieved by the working winding alone. Therefore, an additional starting windingis introduced into the design, shifted in space relative to the main one by 90 degrees. This design feature is critical to creating starting torque.

The operating winding, often called the main winding, has thicker wire and a higher number of turns, which provides low electrical resistance. It is connected directly to the network and works continuously as long as the refrigerator is on. In contrast, the starting winding is made of thinner wire and has a high resistance. It comes into operation only at the moment of starting through a starting relay or capacitor, and then turns off.

Differences in the physical parameters of the wires make it easy to identify the conclusions using simple measuring instruments. Working winding resistance will always be less than the starting resistance. This is a fundamental rule that works for the vast majority of compressors, whether Atlant, Indesit or more modern inverter models, although in the latter the control circuit may be more complex.

⚠️ Attention: Before any manipulations with the electrical part of the compressor, be sure to disconnect the refrigerator from the mains. Residual voltage in capacitors can be dangerous, so let the equipment stand turned off for at least 10-15 minutes.

It is important to note that in some modern models, especially those with inverter control, the classic division into starting and operating windings may be conditional, since the frequency converter controls the phases differently. However, for standard linear compressors, which make up 90% of the equipment fleet, the method described below is the main one.

Necessary tools for diagnostics

To carry out high-quality diagnostics, you will need a minimum set of tools that every home craftsman should have. The main device will be multimeter (tester), capable of measuring resistance in the range from 0 to 2000 Ohms. It is advisable to use a digital device with audio dialing, as this significantly speeds up the process of searching for contacts.

In addition to the measuring device, you will need screwdrivers to remove the protective casing at the back of the refrigerator, where the compressor is located. Also, pliers and insulating tape or heat shrink for subsequent insulation of connections will not be superfluous. If you plan to start the engine outside the refrigerator, you will need a connection diagram with a starting relay and a capacitor.

Pay attention to the condition of the multimeter probes: they should be intact, without cracks isolation. Before starting work, always check the serviceability of the device itself by connecting the probes to each other - the screen should display a value close to zero. This ensures that you are measuring exactly the engine parameters, and not the instrument error.

Preparing the compressor for testing

The first stage of diagnosis is access to the electrical contacts. The compressor is usually enclosed in a metal casing that is secured with bolts or latches. Carefully remove the cover, being careful not to damage the copper tubes and wiring. At the bottom of the unit you will see a start-up relay and a capacitor that cover the winding terminals.

You need to remove the start relay. It is usually simply slipped onto the three contacts of the compressor and secured with a bracket or spring. After dismantling the relay, three pins arranged in a triangle will open in front of you. These are the winding terminals. On some models, for example Whirlpool or Beko, the contacts may be labeled with the letters C, S, R or marked with color, but you should not rely on the markings, as they may be erased or missing.

Visually inspect the contacts for carbon deposits or signs of overheating. If black deposits or melted plastic are visible on the terminals, this may indicate an insulation breakdown or poor contact in the relay. In such cases, measurements may be incorrect, and it is better to clean the contacts with fine sandpaper before testing.

Methodology for determining the windings with a multimeter

Now we move on to the most important stage - measurements. Set the multimeter to resistance measurement mode (limit 2000 Ohm or 2 kOhm). You need to measure the resistance between all three contacts in pairs. For convenience, we number them conditionally: 1, 2 and 3.

Take three measurements: between contacts 1-2, 2-3 and 1-3. Record the resulting values. For a working engine, the sum of the resistances of the two smaller values ​​should be equal to the third, largest value. This happens because the starting and working windings connected in series give the total resistance of the circuit.

When analyzing the obtained figures, follow the following rule: least resistance corresponds to the working winding, the average is the starting winding, and the largest value (the sum of the first two) is the resistance of both windings together. For example, if the resistance between contacts A and B is 20 Ohms, between B and C is 50 Ohms, and between A and C is 70 Ohms, then the pair A-B is the working winding, B-C is the starting winding, and the common terminal B is common to both.

It is important to understand that specific numbers may vary depending on the engine power and manufacturer. For powerful refrigerator compressors LG or Samsung the resistance may be lower than for low-power models. The main thing here is the ratio of values, not absolute values.

Checking for interturn short circuit and breakdown

Determining the type of winding is only half the task. It is critical to ensure the integrity of the insulation. If the motor has an interturn short circuit, it can hum, overheat and knock out the circuit breaker, even if the resistance formally corresponds to the norm. To check the breakdown on the housing, press one probe of the multimeter to any stripped place on the compressor housing (for example, to a copper tube, stripped to metal), and with the second touch each of the three contacts.

The device should show infinity (one in the most significant digit or overload symbol). If the multimeter shows at least some resistance, even a few Megaohms, this is an alarm. Breakdown to the housing means that the operation of such a refrigerator is life-threatening and requires replacing the compressor.

⚠️ Attention: If, when measuring the resistance between the windings, the device shows zero or a value close to it, this indicates a short circuit inside the coil. Such an engine cannot be repaired.

You should also pay attention to the smell. If a persistent smell of burnt insulation is heard from an open pipe or when the relay is removed, this is a sure sign that the windings have overheated and melted. Visually, the wire may look intact, but its properties have already been changed.

Why does the compressor heat up?

A frequent cause of overheating is not only a short circuit, but also operation in the under-switched mode or increased pressure in the system. However, if the hot case is accompanied by a hum and lack of cold, the probability of a burnt winding is more than 80%.

Specifics of different manufacturers

Different brands use different standards for marking and contact placement. For example, in compressors Danfoss (now Secop), which are often found in refrigerators Indesit and Ariston, the terminals are often arranged in a row and can be marked with colors: black - general, blue or brown - working, red - starting. However, colors may fade, so checking with a multimeter is mandatory.

In units Atlant and Biryusa domestic motors or their analogues are often used, where the terminals are arranged in a triangle. The rule often works here: if you look at the contacts from the relay side, the common terminal is often located on the top or left, but again, you cannot rely on geometry. Electrical resistance is the only reliable guide.

There are also two-phase compressors, where both windings have the same resistance. In such cases, the division into starting and operating is arbitrary, and switching the phase changes the direction of rotation (although this is not used in refrigerators, since the direction is fixed). They are characterized by the presence of a capacitor that is constantly on.

Typical errors in diagnostics

Beginners often make mistakes that lead to false conclusions. One of the most common is measuring resistance without removing the relay. The relay contacts may have their own resistance or be oxidized, which will distort the results. Always take measurements directly at the compressor terminals.

Another mistake is ignoring the engine temperature. The resistance of copper depends on temperature: a cold engine will show some values, a hot one - others. If you just turned off the refrigerator, the resistance may be higher than rated. Allow the unit to cool to room temperature before diagnostics.

Also, do not forget about the quality of the probe contacts. Poor clamping or oxidation of the tips can add extra Ohms, which can become a decisive factor at low winding resistance values. Strip the probes and press them tightly to the terminals.

⚠️ Attention: Technical specifications and connection diagrams may vary slightly depending on the year of manufacture and model modification. Always check the technical documentation for the specific device, if available.

Frequently asked questions (FAQ)

Is it possible to start a compressor without a starting winding?

No, it is impossible to start an asynchronous refrigerator motor without a starting winding or starting device. The rotor will not be able to gain the required speed, the engine will only hum and quickly overheat, which will lead to thermal protection or winding combustion.

What to do if the resistance of the windings is the same?

If the resistance between all pairs of contacts is the same, this may indicate a specific type of motor (two-phase with capacitor start) or, more likely, interturn short circuit that equalizes the resistance. Additional diagnostics with current clamps is required during a test run.

Which wire is thicker: starting or working?

The working winding wire is always thicker, since the main working current flows through it. The starting winding wire is thinner, since it is turned on only for a short start time and has a higher resistance.

Is it possible to swap the starting and working windings?

It is absolutely not possible. If you apply operating voltage to the starting winding, it will burn out almost instantly due to the high resistance and thin wire. If you turn on the working winding through the starting relay, the engine will not start.

Why does the multimeter show infinity on the working winding?

This means an open circuit. The wire inside the winding has burned out or moved away from the contact. It is impossible to restore the winding at home; the compressor needs to be replaced.