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

A sudden stop of the refrigerator often becomes an unpleasant surprise, especially when there are perishable foods inside. One of the most common causes of breakdown is the failure of the electric motor or a violation of its connection, which requires immediate diagnosis. Owners of household appliances are often faced with the need to replace the starting relay or the compressor itself, but without an exact understanding of where the starting and working windingss are located, it is impossible to carry out quality repairs.

Incorrect connection of the terminals can lead to instant combustion of the engine, humming without starting, or knocking out plugs in the electrical panel. That is why the question of how to determine the starting and operating windings of a compressor is fundamental for any home craftsman who decides to carry out independent repairs. Understanding the principles of operation single-phase asynchronous motor will allow you not only to restore the operation of the unit, but also to save significant money on the services of a service center.

In this article we will examine in detail the contact identification methods, the necessary tools and safety measures that are critical when working with high voltage. You'll learn how to properly use a multimeter, interpret resistance readings, and avoid common mistakes made by beginners. A competent approach to diagnostics will extend the life of your refrigerator and ensure its stable operation in the future.

The principle of operation of a single-phase motor and the role of windings

Compressors of household refrigerators are usually equipped with single-phase asynchronous motors that cannot start on their own without additional help. To create the initial torque, the stator has two separate windings: the main winding, called working, and the auxiliary, known as starting. The working winding occupies most of the stator slots and has a larger wire cross-section, which provides it with lower electrical resistance.

The starting winding is made of thinner wire and has a greater number of turns, which is why its resistance is much higher. It is connected to the network only when the engine is started through a special starting device, most often through starting relay or a capacitor. After the rotor reaches about 75% of rated speed, the centrifugal mechanism or relay opens the starting winding circuit, and the motor continues to operate on the main winding only.

⚠️ Attempting to start the compressor by applying voltage directly to the starting winding without a relay or leaving it on into the network constantly, will lead to overheating and interturn short circuit in a matter of seconds.

Understanding this physics of the process helps to understand why the resistance of the windings differs. If we could look inside the stator, we would see that the working winding is wound with copper wire with a diameter of, for example, 0.8 mm, while the starting winding may have a diameter of 0.4 mm. It is this difference in the geometry of the wire and the number of turns that creates different active resistancewhich we will measure.

Necessary tools and safety measures

Before starting any work on diagnosing the electrical part of the refrigerator, you must strictly follow the electrical safety rules. The first and most important step is to completely disconnect the device from the electrical network. It is not enough to simply turn off the refrigerator with a button or thermostat - you need to remove the plug from the socket, since a dangerous potential may remain at the relay contacts.

To take measurements, you will need a minimum set of tools, which most home craftsmen can find. The main device will be multimeter (tester), configured to measure resistance in the range of up to 2000 Ohms. You may also need screwdrivers to remove the compressor protective casing, pliers and possibly pliers to remove the terminals.

• 🛠️ Digital multimeter with working probes and battery.
• 🔧 Set of screwdrivers (cross and flat) for dismantling the plastic casing.
• 🧤 Dielectric gloves for protection against accidental electric shock.
• 📸 Smartphone for photographing the connection diagram before disassembling.

Particular attention should be paid to the condition of the wire insulation. If you see melted areas, cracks in the insulation, or blackened contacts, you cannot continue using such equipment. Before taking measurements, make sure that the capacitor (if there is one in the circuit) is discharged, although in modern refrigerator circuits it is often built into the relay housing or absent.

⚠️ Attention: Do not touch the metal parts of the multimeter probes during measurements. The resistance of the human body can distort the readings of the device, which will lead to an incorrect diagnosis.

Visual identification and access to contacts

The process of identifying windings begins with gaining physical access to the contact group of the compressor. It is usually hidden under a plastic or metal casing at the bottom rear of the refrigerator. After removing the cover, you will see a black cylindrical motor housing, to which a start-up relay block is attached to the side or top.

Carefully remove the relay. Depending on the refrigerator model (for example Atlant, Indesit or Beko), the relay can be held on by spring brackets, screws, or simply sit tightly on the terminals. Be careful: contacts may be fragile. After dismantling the relay, three terminals arranged in a triangle will open in front of you.

Often there are markings on the terminals, but they can be erased, contaminated with oil, or be missing altogether. The standard marking is as follows: C (Common) - common wire, R (Run) - working winding, S (Start) - starting winding. Some European models use marking 1, 2, 3 or letters M, R, S.

Nuances of marking from different manufacturers

In Danfoss (Secop) compressors, the leads are often arranged in a row and may have color markings on the relay terminals: black, blue, brown. In old Soviet refrigerators, markings could be completely absent, and craftsmen were guided only by the position of the contacts relative to the body.

If the marking is not readable, you cannot rely on it. Visually, one can only approximately guess the purpose of the contacts by their location relative to each other, but only the device will give an accurate answer. It is important to remember or photograph the original position of the wires before disconnecting them, so that if the diagnosis is successful, you can quickly assemble the circuit back.

Method of testing with a multimeter: step-by-step instructions

The most reliable way to determine the starting and operating windings of a compressor is to measure the electrical resistance between the terminals. To do this, switch the multimeter to resistance measurement mode (designation Ω), selecting the limit of 2000 Ohms or 2 kOhms. First you need to find a common point.

Measure the resistance between all three pairs of terminals. You will get three values. The sum of the two smaller resistances should be equal to the third, largest (taking into account the instrument error). The greatest resistance is the sum of the resistances of the starting and working windings, measured between their free ends.

Consider an example: you got the values ​​20 Ohm, 40 Ohm and 60 Ohm.

1. The largest value (60 Ohms) is the resistance between the starting and working terminals.

2. This means that the two terminals, between which 60 Ohms are measured, are not a common wire.

3. The third terminal, which did not participate in the 60 Ohm measurement, is common wire (C).

Now, knowing the common wire, we measure the resistance from it to the other two.

- The resistance between the common and working terminals will be the smallest (in our example, 20 Ohms).

- The resistance between the common and starting pins will be average (in our example 40 Ohms).

Thus, the pin with the least resistance relative to the common is working winding (R). The output with more resistance (but less than the sum) is starting winding (S). This method works for 99% of serviceable single-phase refrigerator motors.

Table of typical resistance values

To facilitate diagnostics, we provide a table with approximate values resistances for compressors of various capacities. Remember that exact numbers may vary depending on the manufacturer, winding temperature and specific engine model.

If your measurements differ radically from the tabulated ones (for example, they show several ohms or, conversely, megaohms), this is a signal of a malfunction. A resistance of several ohms indicates turn-to-turn short circuit, and an infinitely high resistance indicates an open circuit. In both cases, the compressor requires replacement or professional rewinding.

⚠️ Attention: The resistance of the windings depends on the temperature. On a cold engine the values ​​may be lower, on a hot engine they may be higher. Allow the compressor to cool to room temperature before taking measurements to obtain accurate data.

Fault diagnosis: break and breakdown to the case

In addition to correctly identifying the pins, the master must be able to diagnose the insulation condition. A breakdown on the body is a dangerous malfunction that can lead to electric shock when touching the metal parts of the refrigerator. To check, switch the multimeter to the continuity mode or to the maximum resistance limit (20 MOhm).

Press one probe to any of the three terminals (after cleaning the contact area), and touch the copper tube of the compressor with the other (after cleaning a small stain of paint and rust). The device must show infinity (one in the most significant digit or symbol OL). Any other value indicates an insulation failure.

Another common problem is thermal protection. A thermal relay may be built inside the compressor, which opens the circuit when it overheats. If the multimeter shows a break at all points, wait 30-40 minutes until the engine has completely cooled down and repeat the measurements. If the break persists, the engine is faulty.

It is important to distinguish a working engine from a burnt-out one. If the resistance of the starting winding is significantly higher than normal (for example, 2-3 times), this indicates burning of the contacts or the beginning of the wire burnout process. Such a compressor may hum, but not start, or start only with a push, which is unacceptable for operation.

Connection diagram and startup after diagnostics

After you have managed to determine the starting and operating windings, you need to correctly assemble the circuit. The starting relay is placed on the terminals strictly in a certain position, which is usually indicated by an arrow UP or TOP. A mixed up relay will not work or will burn out.

The connection diagram is simple: phase and neutral from the network go to the relay contacts. From the relay, the phase is supplied to the working winding constantly, and to the starting winding only at the moment of startup. The common wire is connected directly to the network (via a thermostat and protection). An error in connecting the common wire will result in the 220V voltage going directly to the starting winding.

For a temporary start (for testing only!), some craftsmen use a button that simulates the operation of a relay, but doing this without experience is strictly not recommended. It is better to use a standard or new starting relay, selected according to the power of the compressor.

• 🔌 Make sure that the relay is put on all the way and secured with a bracket.
• 🔩 Check the tightness of the terminals to the compressor terminals.
• ⚡ Plug in the refrigerator via wattmeter or ammeter to monitor the starting current.

The starting current of a working compressor is 3-5 times higher than the working one, but lasts only 1-2 seconds. If the humming continues longer and the refrigerator is not cooling, immediately turn off the power. This means that the rotor has not moved out of place, and the windings are heating up.

What to do if the resistances of the windings are the same?

In rare cases (usually in industrial or specific models), the resistances of the starting and operating windings may be close. In household refrigerators this is almost impossible. If you see the same values, most likely you are measuring the wrong contacts or the motor has a hidden defect (a turn short has equalized the resistance). Test the device on a known-good load.

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

Theoretically, it is possible by manually briefly applying current to the starting winding, but this is dangerous and ineffective. Without a relay, the engine will not reach the required speed and will quickly burn out. In addition, in modern circuits, the relay is often combined with thermal protection, the absence of which is unacceptable.

Why does it buzz, but does not start after replacing the relay?

There may be several reasons: the piston compressor is jammed (mechanical failure), the starting winding is faulty (break or short circuit), or low voltage in the network. It is also possible that a relay with incorrect characteristics was selected for a given motor power.

How to determine the common wire if there is no marking and the circuit is lost?

Only by measuring resistance, as described above. Find the pair with maximum resistance - these are the ends of the starting and working windings. The third, remaining wire is common. Then measure the resistance from the total to each of the pair: where less is the working one, where more is the starting one.

Does the order of connecting phase and zero affect the operation of the compressor?

For a single-phase asynchronous motor, the order of connecting phase and zero to the general circuit is not important, it will rotate in one direction. However, within the relay circuit and windings, polarity is important for proper operation of the trigger mechanism. Follow the markings on the relay and compressor.