The situation when the refrigerator stops cooling, and the motor hums, but does not start, or is completely silent, often indicates a problem with the electrical circuit of the motor. Before replacing an expensive unit, experienced craftsmen always diagnose the integrity of the coils. Determination of refrigerator compressor windings - this is the primary and mandatory stage of testing, which allows you to identify an interturn short circuit or wire break. Without understanding which terminal is responsible for what, it is impossible to correctly connect the starting relay or diagnose a malfunction.
Inside the sealed casing, an electric motor is hidden, which has three terminals that go out through insulators. These contacts are designed to connect to a 220 volt network through the starting system. If you mix them up, the motor will either burn out instantly or start working in the opposite direction, which will lead to destruction of the mechanical part. Therefore, knowledge of markings and the ability to use measuring instruments is critical for safe repairs.
In this article we will examine in detail the method of searching for Common, Start and Run contacts, consider typical resistance values for different manufacturers and answer common questions that arise during diagnostics. Correct pin identification will save you time and money by allowing you to accurately determine whether your Atlant, Indesit or LG needs a new motor.
Motor design and pin locations
The refrigerator compressor is a sealed unit with a motor-compressor inside. The electrical part of the motor consists of a stator with windings and a rotor. On the outside of the case, usually under a plastic cover or next to the start relay, there is a contact block with three terminals. It is to them that the voltage is applied to create a magnetic field that rotates the rotor.
These three contacts are not random, each of them has a strictly defined purpose in the electrical circuit. The two windings inside the motor differ in wire thickness and number of turns, which directly affects their electrical resistance. One of them is designed for continuous operation, and the second is turned on only for a short time to create a starting torque.
⚠️ Attention: Never try to start the compressor by applying voltage to all three contacts at once or bypassing the starting relay. This is guaranteed to lead to a short circuit of the windings and failure of the motor.
The location of the pins on different models may differ. Some manufacturers, such as Secop (formerly Danfoss) or Embraco, the contacts can be arranged in a triangle or in a row. It is important to understand that the physical location of the pins on the terminal block does not always correlate with their purpose, so you cannot rely only on the visual order “from left to right.”
Necessary tools and preparation for diagnostics
To carry out high-quality diagnostics, you will need a minimum set of tools that any home craftsman can find. The main device is a multimeter (tester) capable of measuring resistance in the range from 0 to 2000 Ohms. Without this device, it is almost impossible to determine the integrity of the circuit and the type of winding, since a visual inspection does not provide information about the internal state of the wire.
In addition to the multimeter, you will need screwdrivers to remove the protective cover of the compressor and the insulating box. If there are oxides or traces of carbon on the terminals, they must be carefully cleaned with fine sandpaper or a file until they have a metallic shine. Poor contact of the probes with the terminals can distort the readings of the device, which will lead to erroneous conclusions.
It is also important to ensure good access to the compressor. In some refrigerator models, for example, old ZIL or Biryusa, the motor may be very dusty or covered with an oil film. Wipe the surface with a dry cloth to avoid moisture or dirt getting inside the electrical part when removing the relay.
☑️ Preparation for testing
Marking of contacts: letter designations
Most modern manufacturers apply international marking standards, applying letter designations directly on the compressor housing or on a plastic block. Understanding these abbreviations is the quickest way to determine the pin assignment, as long as the label is readable. English abbreviations are usually used, which are derived from the functional purpose of the contact.
The most common designation is "C" (Common), which means common wire. It is to this that one of the phase wires of the network is connected. The other two pins are marked as "S" (Start) - starting winding, and "R" (Run) - working winding. In some circuits, especially those made in Asia, you can find the designation "M" (Main) instead of "R" for the working winding.
Below is a table of marking correspondence for different brands, which will help you not get confused when repairing equipment of different years of manufacture:
| Winding type | Standard marking (ENG) | Alternative marking | Russian analogue (schemes) |
|---|---|---|---|
| General | C (Common) | - | O (General) |
| Start | S (Start) | L (Line - rarely) | P (Start) |
| Working | R (Run) | M (Main) | R (Working) |
| Earth | GND / ⏚ | Earth | Z (Earth) |
If the markings have been erased over time or are filled with oil, you cannot rely on the letters. In such cases, the only correct way is to measure the resistance between pairs of contacts. It is also worth noting that the fourth contact, if it exists and is not included in the triangle of the three main ones, is usually a thermal protection terminal or case grounding.
Method of testing with a multimeter
When visual markings are missing or are in doubt, a multimeter comes into play. Switch the device to resistance measurement mode (Ohm), selecting the limit of 2000 Ohm or 2 kOhm. First, make sure that the device is working by connecting the probes to each other - it should show zero or a value close to zero.
The determination process begins by searching for the pair of contacts that gives the greatest resistance. To do this, alternately apply the probes to any two of the three terminals, writing down or remembering the readings. You need to find two contacts between which the resistance is maximum. These two terminals are the ends of the series-connected starting and working windings.
The third contact, which did not participate in measuring the maximum resistance, is common terminal (C). From it to the other two contacts the resistance will be less. Next, we measure the resistance from the common terminal to each of the remaining two. The contact where the resistance is lower is the working winding (R), and where it is higher is the starting winding (S). This rule works for 95% of single-phase compressors.
⚠️ Attention: If the multimeter shows one (infinity) on any pair of contacts, this indicates a winding break. Such a compressor cannot be repaired at home and requires replacement.
For clarity, let's look at the algorithm of actions. Let's say we have three contacts: 1, 2 and 3.
Measurement 1-2: 30 Ohm.
Measurement 2-3: 10 Ohm.
Measurement 1-3: 20 Ohm.
In this case, pair 1-2 gives the maximum value (30 Ohms), which means that contact 3 is common (C).
Now we look from contact 3: to contact 2 - 10 Ohms (less, that means R), to contact 1 - 20 Ohms (more, that means S).
Why are the resistances different?
The working winding is wound with a thicker wire and has fewer turns, so its resistance is lower. The starting winding is thinner and longer, which gives more resistance and is necessary to create a phase shift at start.
Typical resistance values for different brands
Although the measurement principle is the same for all, the absolute resistance values may vary depending on the power of the motor and the manufacturer. For low-power compressors used in small refrigerators, certain values are typical, for powerful units Liebherr or Siemens others. Understanding these ranges helps to quickly diagnose a malfunction.
It is considered normal if the sum of the resistances of the starting and operating windings is approximately equal to the resistance measured between the outer contacts (S and R). Small deviations are acceptable due to instrument error and engine temperature. However, if you see values of several Ohms or, conversely, hundreds of Ohms, this is a reason to be wary.
The following are approximate data for popular models:
- 🔹 Secop (Danfoss): Working winding 10-15 Ohm, starting winding 20-35 Ohm. Typical for middle-class refrigerators.
- 🔹 Embraco: Operating 8-12 Ohms, starting 18-25 Ohms. Often found in technology Indesit and Ariston.
- 🔹 Atlant: Working 12-18 Ohms, starting 25-40 Ohms. Belarusian compressors often have slightly higher values.
- 🔹 LG / Samsung: Operating 9-14 Ohms, starting 20-30 Ohms. Asian manufacturers strictly follow the standards.
It is important to consider that resistance may vary slightly depending on engine temperature. On a “cold” compressor the values will be slightly lower, on a “hot” compressor – higher. If you have just tried to start the motor, let it cool for at least 30-40 minutes before checking again.
Fault diagnosis and breakdown on the housing
In addition to checking the integrity of the windings, it is critical to ensure that there is no insulation breakdown on the compressor housing. This is a situation where the electric current does not flow through the windings, but directly to the metal casing. This phenomenon is life-threatening and can lead to electric shock when touching the refrigerator.
To check the breakdown, switch the multimeter to the dialing mode (with sound) or resistance measurement to the maximum limit (2000 kOhm or 20 MOhm). Press one probe to any of the three contacts, and the second to the place on the compressor housing that has been cleared of paint (you can use a copper tube fitting).
The device should show infinity (one in the most significant digit). If you hear a squeak or see any resistance readings other than infinity, the insulation has failed. It is prohibited to operate such a refrigerator.
⚠️ Attention: Sometimes breakdown appears only when heated. If a “cold” compressor rings normally, but trips the RCD after 10-15 minutes of operation, most likely thermal expansion destroys the insulation inside. The unit needs to be replaced.
It is also worth checking the condition of the starting relay. Often the problem lies not in the motor itself, but in a stuck contact or a burnt-out posistor inside the relay. If the windings are intact, but the refrigerator does not start, try to gently shake the relay - if you hear the ringing of the ceramic element, it needs to be changed.
Frequently asked questions and answers from technicians
Is it possible to start a compressor without a relay, directly from the network?
Theoretically, you can start it by applying voltage to the working winding and briefly to the starting winding, but do this manually extremely dangerous and not recommended. Without the correct phasing and shutdown timing of the starting winding, the motor will burn out in a few seconds. There are special test devices with a button, but for the average user it is safer to use a standard relay.
What to do if the winding resistance differs greatly from the tabulated data?
Small deviations (10-15%) are acceptable. However, if the resistance of one of the windings is significantly lower than normal (for example, 2 Ohms instead of 10), this is a sign of an interturn short circuit. Such a compressor will consume increased current, overheat and quickly fail. It needs to be replaced.
Is it possible to determine the windings without a multimeter?
It is reliably (reliably) impossible to do this without a measuring device. The "poke" method of connecting to a 220V network will either burn out the windings or cause electric shock. The only visual indication is the thickness of the wire inside (if the winding is visible), but this is not applicable in a sealed case. Buying a cheap multimeter will pay off with the first successful diagnosis.
Why does it hum, but does not start, although the windings are intact?
If the electrical part is intact, the problem may be mechanical: the piston group is jammed, the oil has dried out, or a plug has formed in the capillary. The starting relay is also often to blame because it does not provide a starting impulse. Try replacing the relay with a known good one of a similar series.