When the refrigerator stops freezing and the compressor does not start or hums without result, the first thought is that the motor winding has burned out. But before replacing a part, you should make sure that the problem is in it, and not in the relay, thermostat or wiring. Determination of the working and starting windings of the compressor is a key diagnostic step that you can perform independently, having a multimeter and basic knowledge of electrical engineering on hand.
In this article Let's look at the search for the working winding (it is also called three reliable methods searching for the working winding (also called main or main), which work for 90% of household refrigerators - from Soviet "Minsk" and "Biryusa" to modern LG, Samsung i Atlant. Let's consider not only the theory, but also typical mistakes of beginners that lead to false conclusions. For example, why the winding resistance can “float”, how to distinguish an interturn short circuit from an open circuit, and what to do if there are no standard markings on the compressor terminals.
Important: if you have never worked with electricity, it is better to entrust the diagnostics to a specialist. Direct connection of the compressor to a 220V network without a starting relay or through incorrectly defined windings can lead to a shock electric current, fire or motor failure.
1. Refrigerator compressor design: where the windings are located
A refrigerator compressor is asynchronous electric motor in a sealed housing that pumps refrigerant through the system. There are two windings inside it:
- 🔹 Working (main, R) —constantly connected to the network, creates a magnetic field to rotate the rotor.
- 🔹 Start (S) —connected briefly through a relay, “pushes” the rotor at a moment start.
The third terminal is Common point (C), where the windings are connected inside the compressor. On the motor body you will see three terminals (sometimes four if there is thermal protection), marked with letters or numbers. Standard pinout:
| Terminal | Designation | Purpose |
|---|---|---|
| 1 | C (Common) | Common connection point of windings |
| 2 | S (Start) | Starting winding |
| 3 | R (Run) | Working winding |
However, in practice there may be no markings (especially on old or Chinese compressors). In this case, the windings are determined by resistance or visually —more on this in the following sections.
2. Method 1: Determining windings by resistance (with a multimeter)
This is the most reliable method that works for 99% of compressors. You will need digital multimeter (analog will not work due to low accuracy). Algorithm of actions:
- Disconnect the refrigerator from the mains and discharge the capacitor (if there is one in the circuit).
- Remove the start-up relay from the compressor - it is usually attached to latches or one bolt.
- Clean compressor terminals from oxidation (use sandpaper or a file).
- Set the multimeter to resistance measurement mode (range
200 Ohm).
Now measure the resistance between all pairs of terminals. Typical values for household compressors:
| Pair of terminals | Resistance | What does it mean |
|---|---|---|
| C → S | 15–40 Ohm | Starting winding resistance |
| C → R | 10–20 Ohm | Resistance of the working winding |
| S → R | Sum of the two previous ones (25–60 Ohms) | Resistance between the windings |
How to distinguish the working winding: it always has lower resistancethan the starting one. For example, if 12 Ohms were measured between terminals 1 and 2, and 25 Ohms between 1 and 3, then:
- 🔹 Terminal 1 - general (C).
- 🔹 Terminal 2 - working (R) (lower resistance).
- 🔹 Terminal 3 - starting (S).
Measure the resistance between all pairs of terminals|Record the values|Compare: the working winding always has less resistance|Check for an open circuit (infinite resistance) or short circuit (0 Ohm)-->
⚠️ Attention: If the resistance between any terminals is equal to zero - there is an interturn short circuit in the compressor. If infinity, the winding is broken. In both cases, the motor must be replaced.
3. wires
If you don’t have a multimeter at hand, you can try to determine the windings “by eye.” To do this:
- Remove the cover from the start-up relay (if it is removable).
- Inspect the wires going from the compressor to the relay.
- 🔹 Thick wire (cross-section 0.8–1.2 mm) - goes to working winding (lower resistance → more current → thicker wire).
- 🔹 Thin wire (cross-section 0.4–0.6 mm) - goes to starting winding.
- 🔹 The third wire (if any) is common (
C).
This method works for 70–80% of compressors, but there are exceptions:
- 🔹 In some models Danfoss or Embraco the wires may have the same cross-section.
- 🔹 On Chinese compressors (for example, R134a) there are often no markings, and the wires hidden under heat shrink.
⚠️ Attention: If you see traces of insulation melting or blackening on the terminals, this is a sign turn-to-turn short circuit. Such a compressor cannot be repaired.
What to do if the wires are the same?
In this case, the visual method will not work. You will have to either use a multimeter (method 1) or temporarily connect the compressor through the starting relay and observe the current. The working winding will consume more amperes during operation (measured with a current clamp).
4. Method 3: Test by connecting to the network (for experienced)
This method requires caution and is used only if the first two methods do not produce results. You can connect the compressor directly to a 220V network only through a starting relay or for a short time (no more than 1–2 seconds)! Algorithm:
- Disconnect the refrigerator from the network.
- Remove the start-up relay and connect the wires with the plug to the compressor:
- 🔹 One wire - to common terminal (C).
- 🔹 The second wire - alternately on S (starting) and R (working).
When connected to working winding compressor:
- 🔹 It will start to hum, but will not start (there is not enough starting torque).
- 🔹 Consumes current ~1–1.5 A (can measure with a current clamp).
When connected to starting winding:
- 🔹 Compressor does not buzz or makes a quiet buzzing sound.
- 🔹 Current consumption ~0.5–0.8 A.
⚠️ Attention: Do not hold the compressor is connected for longer than 2-3 seconds - this can lead to overheating of the windings. If the motor does not start even with a short-term connection to C and S at the same time, a malfunction is likely (rotor jamming or breakage).
5. Typical mistakes when determining windings
Even experienced craftsmen sometimes make mistakes that lead to false conclusions. Here are the most common:
- 🔹 Ignoring terminal oxidation. Oxides create additional resistance, which can cause multimeter readings to be incorrect. Always clean the contacts!
- 🔹 Measuring resistance with a relay connected. The relay has its own resistance, which distorts the results. Always remove it before checking.
- 🔹 Confusion with markings. On some compressors, the terminals are not designated
C-S-R, butM-S-Cor numbers. Always check the documentation for the model. - 🔹 Neglecting temperature. The winding resistance depends on temperature. If the compressor is cold, the readings may differ by 10–15% from the nominal ones.
Another common mistake is checking the windings without discharging the capacitor. If there is a capacitor in the circuit (such as in inverter compressors), it may remain charged and damage the multimeter. Always discharge it by shorting the terminals with a screwdriver with an insulated handle.
6. How to check windings for an interturn short circuit
An interturn short circuit (between the turns of one winding) is one of the most insidious faults. It is difficult to diagnose with a multimeter, since the winding resistance may remain normal. Signs of an interturn short circuit:
- 🔹 The compressor buzzes, but does not start.
- 🔹 The motor housing gets hot after 5-10 minutes of operation.
- 🔹 Start relay clicks and turns off the power.
- 🔹 Current consumption higher rated (for example, 2.5 A instead of 1.5 A).
How to check:
- Measure the current consumption of the compressor in operating mode (via a relay).
- Compare with the rated current indicated on the compressor nameplate (for example, "1.2 A").
- If the actual current is 30–50% higher, an interturn short circuit is likely.
For accurate diagnosis, use megohmmeter (insulation test at 500 V) or oscilloscope (analysis of the current shape is difficult to do at home, so if an interturn fault is suspected). short circuit, it is better to replace the compressor.
7. Table of winding resistances for popular compressors
The following are approximate resistance values for common models. Please note that actual figures may differ by ±10% depending on the modification and condition of the motor.
| Compressor brand | R (working), Ohm | S (starting), Ohm | C → S + R, Ohm |
|---|---|---|---|
| Danfoss NL6 | 12–15 | 20–25 | 32–40 |
| Embraco EG80 | 9–12 | 18–22 | 27–34 |
| Secop (DWM) SC10 | 10–14 | 25–30 | 35–44 |
| LG Inverter (LW08) | 8–10 | 15–18 | 23–28 |
| Atlant (KSh-140) | 14–18 | 28–35 | 42–53 |
⚠️ Attention: The data in the table is provided for reference. For exact values, see the technical documentation for your compressor model.
FAQ: Frequently asked questions
Is it possible to determine the windings without a multimeter?
Yes, but with less accuracy. Use the visual method (based on the thickness of the wires) or a short-term connection to the network (only for experienced ones!). However, without measuring the resistance, you will not be able to detect a break or an interturn short circuit.
What to do if the resistance of the windings the same?
This is abnormal and indicates a malfunction. Possible reasons:
- 🔹 Interturn short circuit in both windings.
- 🔹 Break with subsequent “ringing” through the housing.
- 🔹 Multimeter malfunction (check with a known resistor).
In any case, the compressor needs to be replaced.
How to distinguish a compressor with thermal protection?
On such models there is a fourth terminal or an additional wire going to thermal protection relay (usually black). When overheated, it opens the circuit. Before checking the windings, turn off the thermal protection, otherwise it will distort the multimeter readings.
Why does the compressor hum but does not start if the windings are working?
There are several reasons:
- 🔹 Rotor jamming (mechanical blockage).
- 🔹 Low/high pressure in the system (freon leak or capillary tube blockage).
- 🔹 Faulty starting relay (does not close the starting winding).
- 🔹 Weak voltage in the network (less than 200 V).
Check the voltage with a voltmeter terminals of the compressor when starting - it should not be lower than 190 V.
Is it possible to start the compressor without a starting winding?
No. The starting winding creates an initial torque. Without it, the rotor will not move, and the working winding will consume increased current, which will lead to overheating. As a last resort, you can short-term (1-2 seconds) apply voltage to the working winding to check the mechanics, but no more.