If your refrigerator suddenly stops freezing, and only a quiet hum or clicks are heard from the back of the unit, the problem most likely lies in the electrical circuit of the motor. In most cases, the culprit is starting relay or a violation in the windings of the compressor itself. For self-diagnosis and replacement of faulty elements, it is critical to understand which wire leads where and how the motor terminals differ from each other.
The refrigerator motor is an asynchronous electric motor that cannot start on its own without the help of a starting mechanism. Inside its stator there are two main inductors: working and starting. Confusion in their definition when connecting can lead to instant burnout of the insulation or failure of the protection relay, so the issue of pin identification is paramount in any repair.
In this article we will analyze in detail the physical differences of the windings, methods for checking them using a multimeter and nuances that will help you avoid fatal errors when restoring the functionality of equipment. You will learn to accurately identify contacts C, R and S, even if the markings on the case have been erased.
The principle of operation and design of stator windings
To understand which winding is the starting winding, it is necessary to briefly consider the design of a single-phase asynchronous motor. The motor stator has a core with grooves in which copper wire is laid. This wire forms two independent circuits located at an angle of 90 degrees to each other in the stator space. The first circuit is called main or working, it is designed to create the main magnetic flux when the engine is running.
The second circuit, known as starting winding, has fundamental design differences. It is connected to the network only when the rotor starts and is turned off by a centrifugal switch or thermal relay when the engine reaches about 75% of the rated rotation speed. If both windings were the same, a rotating magnetic field would not arise, and the rotor would only hum, remaining motionless.
The main physical difference lies in the parameters of the wire. The working winding is wound with a thicker wire, since it experiences a constant current load while the refrigerator is operating. The starting winding is made of a wire of smaller diameter, but with a large number of turns. It is this design solution that creates the necessary phase shift for starting, but does not allow it to work for a long time under load.
Why can’t you keep the starting winding on for a long time?
If the starting relay gets stuck and does not turn off the starting winding after starting the motor, it will begin to overheat. A thin wire will not withstand prolonged current flow, the insulation will melt, and an interturn short circuit will occur, which will lead to expensive repairs or replacement of the compressor.
Visual and physical differences between the terminals
Primary diagnosis begins with a visual inspection of the compressor contact group. On most modern and old models of refrigerators, such as Atlant, Indesit or Stinol, the terminals are marked, although over time it can be erased or oxidized. Typically, contacts are designated in Latin letters: C (Common) - general, R (Run) - working, S (Start) - starting.
If there is no marking, you can determine the purpose of the pins by their location on the terminal block. In a standard triangular pinout, the common wire (C) is often located separately from the start and run pin pair. However, relying solely on contact geometry is dangerous, since manufacturers may change the configuration in different series of motors.
A more reliable method is to estimate the thickness of suitable wires if the motor has not yet been completely disassembled. The wire going to the working winding will be visually thicker. It is also worth paying attention to the internal structure: the starting winding is often wound on top of the working winding, so it is closer to the outer diameter of the stator, which facilitates heat removal during short-term operation.
Diagnostics with a multimeter: measuring resistance
The most accurate and safe way to determine which winding is the starting winding is to measure the active resistance using a multimeter. To carry out the procedure, it is necessary to remove the start-up relay and provide access to the three contacts of the compressor. Switch the device to the resistance measurement mode (Ohm) to a limit of up to 2 kOhm.
The measurement process consists of testing pairs of contacts. You need to alternately apply the probes to different pairs of terminals and record the readings. The sum of the resistances between any two pairs of contacts must be equal to the resistance of the third pair when measured through the common wire. But for quick diagnostics, it is enough to remember the golden rule: the starting winding always has greater resistancethan the working one.
Typical values for household refrigerators are as follows: the resistance of the working winding is from 10 to 30 Ohms, while the starting winding is from 30 to 90 Ohms. The difference can be twofold or even threefold. If the multimeter shows infinity (one on the screen), then there is a break in the circuit and the engine must be replaced.
☑️ Algorithm for testing the compressor
Consider an example. You have measured three values between the pins: 25 ohms, 45 ohms and 20 ohms. The logic is simple: the largest value (45 Ohms) is the sum of the resistances of the two windings, measured between the working and starting terminals. The two smaller values (25 Ohms and 20 Ohms) are the resistance of each winding relative to the common wire. Therefore, 25 Ohms is the starting winding (the larger of the two), and 20 Ohms is the working winding.
Resistance table and connection diagram
For ease of data systematization, we present a table with typical resistance values for various types of compressors. Remember that data may vary depending on the motor power and manufacturer (for example, Secop, Embraco, Danfoss).
| Winding type | Marking | Typical resistance (Ohm) | Wire diameter |
|---|---|---|---|
| Operating (Main) | R / Run | 10 – 35 Ohm | Thick (0.6–0.9 mm) |
| Start | S / Start | 30 - 90 Ohm | Thin (0.3–0.5 mm) |
| Common | C / Common | — | — |
| Case (Earth) | — | Infinity | — |
The connection diagram also depends on the type of starting device used. In refrigerators with capacitor starting, the starting circuit. the winding works constantly together with the capacitor, which changes its thermal characteristics. In a classic circuit with a posistor (PTC) or an electromagnetic relay, the starting winding circuit is broken immediately after start.
Typical faults and their symptoms
Understanding which winding is responsible for what helps to diagnose the nature of the breakdown. If the starting winding is burned out, the refrigerator will stop starting. You will hear the hum of the motor, which is trying to start, but after a few seconds the thermal relay will click, and the process will repeat again after a while. time.
An inter-turn short circuit in the working winding causes the engine to hum, it can start, but quickly overheats and knocks out the circuit breaker. In this case, the resistance will be below normal. A breakdown to the frame (short circuit of the winding to the metal frame of the compressor) is the most dangerous malfunction that can lead to an electric shock when touched. refrigerator.
- 🔥 Open winding: The compressor hums, but does not spin, the relay clicks, there is no resistance between S and C (infinity).
- ⚡ Short circuit of the working winding: The engine gets very hot, consumes increased current, the R-C resistance is abnormally low.
- 🛡️ Break on the body: The multimeter shows the resistance between any contact and the copper tube or housing (should be infinity).
⚠️ Attention: Before When performing any work on the continuity of the windings, make sure that the refrigerator is completely disconnected from the electrical network. Residual voltage in the capacitors or accidental plugging into the socket while touching the contacts with the probes can lead to electric shock or failure of the multimeter.
Specifics of modern inverter compressors
Modern models of refrigerators are increasingly There are linear and inverter compressors. Their operating principle differs from classical asynchronous motors. There is no usual division into starting and operating windings in the traditional sense, since the shaft rotation speed is controlled by an electronic control unit.
Checking such motors with a conventional multimeter often does not give the full picture. The winding resistance in inverter compressors (LG Linear, Samsumg Digital Inverter) can be very low (less than 10 Ohms) and the same in all three phases. An attempt to start such a motor directly from a 220V network will lead to its immediate combustion.
Diagnosing inverter systems requires special equipment that supplies signals of a certain frequency. If you are faced with a malfunction of an inverter refrigerator, it is better to limit yourself to checking the windings for breakdown on the housing and the absence of breaks, and entrust further diagnostics to a service center.
Is it possible to replace a conventional compressor with an inverter one?
Theoretically it is possible, but this requires a complete replacement of the control board and reprogramming the refrigerator electronics. Economically, such a replacement is impractical; it is easier to install a similar type of compressor.
Common mistakes during self-repair
Beginners often make the mistake of confusing the contacts when installing a new start relay. If you mix up the starting and working windings, the engine may start in the opposite direction (which is critical for a piston compressor and leads to valve failure) or simply burn out after a few minutes of operation due to overheating of the thin wire of the starting winding.
Another common mistake is ignoring the state of the contacts. Oxidized or burnt terminals add unnecessary resistance, causing heat and false diagnostic readings. Always clean the contacts with fine sandpaper before taking measurements.
⚠️ Attention: Never leave the starting winding plugged in for more than a few seconds outside of the operating cycle. This is guaranteed to lead to its burnout. Use the forced start button only briefly to check.
It is also worth mentioning the quality of insulation. With prolonged use or exposure to moisture, the insulation resistance may drop. If the multimeter shows a current leakage to the housing even of several Megaohms, it is dangerous to operate such a compressor.
Replacement and fault prevention
If the diagnostics showed a break or an interturn short circuit, the only way out is to replace the compressor. Rewinding refrigerator motors at home is impossible due to the need to use special equipment for pressing and vacuuming the system.
To extend the service life of the windings, it is recommended to keep the condenser on the back wall of the refrigerator clean. Dust and animal hair impair heat transfer, the motor overheats, and the insulation of the windings is destroyed faster. Regular cleaning behind the refrigerator is the best prevention.
When installing a new compressor, be sure to check the resistance of the windings of the new unit. It must correspond to the passport data or be similar to the burnt one (taking into account the measurement error). Installing a defective or unsuitable motor will lead to repeated breakdown.
What to do if the resistance of the windings is the same?
In classic asynchronous motors, the resistance of the starting and operating windings cannot be absolutely the same. If the multimeter shows equal values (for example, 20 ohms each), this may indicate a specific motor design (rare) or, more likely, a turn-to-turn short in one of the windings, equalizing the resistance. It is also worth checking the accuracy of the device.
Is it possible to start a refrigerator without a starting relay?
Theoretically, you can start the engine for a short time by applying current to the starting winding manually through a button, but you cannot operate the refrigerator in this mode. Without a relay, the starting winding will not turn off and will burn out in a few minutes. In addition, the thermal protection of the motor will not work.
Why does the compressor hum, but does not start?
This is a classic sign of jamming of the mechanical part of the compressor (piston group) or a malfunction of the starting device. If the windings are intact (resistance is normal), the problem is most likely in the relay or mechanical wedge. Attempts to “pump up” the compressor by applying increased voltage often lead to its final failure.
What resistance is considered normal for an old refrigerator?
For old Soviet-made models (for example, with compressors SK or BPO) the resistance of the working windings may be lower, about 15-20 Ohms, and starting - 30-40 Ohms. The main rule remains the same: the starting one always has greater resistance than the working one.