How to determine the starting and operating windings of a refrigerator compressor: 3 working methods

When the refrigerator stops freezing, but the motor hums or the relay clicks, the problem often lies in compressor windings. The starting and working coils are the “heart” of the engine, and their incorrect connection can damage the equipment forever. Experienced craftsmen determine the conclusions “by eye” or according to the diagram, but what should beginners do?

In this article you will find three proven methods winding identification - from simple visual inspection to precise measurements with a multimeter. We will figure out how to distinguish starting (start) winding from working (main), even if the markings on the compressor are erased. You will also find out what errors during testing lead to instant combustion of the motor the first time you turn it on —and how to avoid them.

Important: all methods are suitable for compressors Danfoss, Secop, Embraco, as well as domestic models Atlant, Biryusa, Saratov. But before starting work, be sure to disconnect the refrigerator from the network and discharge the capacitors - more about this in the section on safety.

1. Visual inspection: where to look for winding markings

Let's start with the simplest thing - studying the compressor housing. For most modern models, the winding terminals are marked with letters or the color of the insulation. Here's what the standard designations mean:

• 🔹 S (Start) - starting winding. Often marked red or orange wire.
• 🔹 R (Run) - working winding. Usually this is black, brown or blue wire.
• 🔹 C (Common) - general conclusion. Maybe white or yellow, sometimes not marked.

If there are no letter designations, inspect the terminal block: on many compressors Embraco i Danfoss the starting winding is located on the left (if you look at the connector from above), and the working winding is on the right. But this rule does not always work: in some models Atlant the connectors are mirrored.

Unfortunately, on old Soviet compressors (KSh-120, DXM-3), the markings could have been erased over decades of use. In this case, the visual method is useless - go to the next step.

2. Checking resistance with a multimeter: an accurate method

This is the most reliable way to determine the windings, but it requires care. You will need a multimeter with a resistance measurement function (ohmmeter). Here are step-by-step instructions:

1. Disconnect the compressor from the network and discharge the capacitor (see how to do this in the safety section).
2. Remove the plastic cover from the terminal block.
3. Measure the resistance between all pairs of terminals. You should get three values:
   • 📊 Minimum (usually 5–20 Ohm) - this is the resistance starting winding.
   • 📊 Average (15-40 Ohm) - resistance working winding.
   • 📊 Maximum (sum of the first two, 20–60 Ohms) - resistance between starting and operating windings (measured through the common terminal).

Example for a compressor Danfoss NL6L:

If all three measurements show the same values (or infinity), this means open or interturn short circuit the compressor is faulty. Also an alarming sign is a resistance of less than 5 ohms (may indicate a short circuit).

Disconnect the refrigerator from the outlet|

Discharge the capacitor (short-circuit the leads with a screwdriver with an insulated handle)|

Clean the terminals from oxidation (with sandpaper or alcohol)|

Set the multimeter to "200 Ohm"|

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3. The “dialing” method with a light bulb: for experienced craftsmen

This method is used less frequently, as it requires the assembly of a simple electrical circuit. It is useful if you don’t have a multimeter at hand, but have an incandescent lamp (220V, 40–60 W) and wires. Attention: the method is dangerous if connected incorrectly!

Algorithm of actions:

1. Connect the lamp in series with the compressor: one wire from the socket to the lamp, the second from the lamp to the intended working winding, the third from the common terminal of the compressor back to the socket.
2. Plug in the circuit for 1-2 seconds. If the lamp lights up brightly, you guessed the working winding. If it barely lights up, this is the starting one.
3. Swap the wires and repeat the test to confirm.

⚠️ Warning: Never connect the compressor directly to 220V without a load (light bulb or starting relay)! This will lead to instantaneous burnout of windings due to lack of current limiting. Also, do not keep the circuit turned on for more than 2-3 seconds - enough for a visual assessment.

Why can’t you use an LED lamp?

LED lamps have too little resistance and do not limit the current in the circuit. When connected through them, the compressor will receive full mains voltage, which will lead to overheating of the windings.

4. How not to mix up the windings when connecting

Even if you have correctly identified the pins, a connection error can be costly. Here are the key rules:

• 🔌 The starting winding always is connected via a starting relay (or posistor). Never apply voltage directly to it!
• 🔌 The working winding is connected to the network via thermal relay (built into the starting or separate).
• 🔌 The common terminal (C) is connected to the neutral wire of the network.

Typical connection diagram for compressors Atlant i Indesit:

220V network
│
├───[Start relay]───[Start winding (S)]
│
├───[Thermal relay]───[Working winding (R)]
│
└───────────────────[Common terminal (C)]

If, after connecting, the compressor:

• ✅ Starts and works stably - everything is connected correctly.
• ❌ It hums, but does not start - check the start relay or swap S and R.
• ❌ Clicks and turns off - there may be a break in the windings or the capacitor is faulty.
📊 What method of determining the windings did you use?
Visual inspection
Multimeter
Light bulb
Another way

5. Safety: how to avoid getting an electric shock

Working with a refrigerator compressor is associated with the risk of electric shock. Here are mandatory precautionary measures:

• ⚡ Unplug the refrigerator from the outlet and remove the plug. Do not rely on the switch - it can only open one phase!
• ⚡ Discharge the start relay capacitor by short-circuiting its terminals with an insulated screwdriver (hold the tool by the plastic part!).
• ⚡ Work with rubber gloves and on a dry surface. Avoid touching metal parts of the housing.
• ⚡ Do not use damaged wires or probes with exposed insulation.

⚠️ Attention: Capacitors in starting relays can retain a charge for up to several hours after the power is turned off. Always check their discharge with a multimeter (voltmeter mode, limit 200V) before starting work.

If you are not confident in your skills, it is better to contact a specialist. The cost of diagnosing windings at a service center (1500–2500 rubles) is often lower than the price of a new compressor (8000–15000 rubles).

6. Common mistakes and how to make them avoid

Even experienced craftsmen sometimes make mistakes when working with windings. Here are the most common mistakes and their consequences:

Error	Consequences	How to avoid
Feeding 220V directly to the starting winding	Overheating and interturn short circuit	Always use a starting relay or posistor
Ignoring capacitor discharge	Electric shock (up to 300V!)	Short-circuit the capacitor leads before work
Connecting the windings without checking the resistance	Short circuit when turned on	Always ring with a multimeter
Use LED lamps for “dialing”	False readings or burning of windings	Take only 220V incandescent lamps

Another typical problem - mixed up wires after repairTo prevent this from happening, take a photograph of the original connection diagram or. mark the wires with colored tape before disconnecting.

7. When the compressor cannot be repaired

Identification of the windings does not always lead to successful repair. Here are the signs that it is time to change the compressor:

• 🚫 The resistance of the windings is zero. (short circuit) or infinity (break).
• 🚫 The compressor hums, but does not create pressure (does not pump freon).
• 🚫 Traces of overheating are visible on the body (blackened paint, melted insulation).
• 🚫 After switching on, it is activated thermal protection (the relay turns off the power after 1-2 seconds).

If the compressor is “jammed” (the rotor does not rotate even when voltage is applied to the working winding), try turning the shaft manually:

1. Remove the protective cover from the rear of the compressor.
2. Turn the shaft clockwise with a screwdriver (through the hole in the bottom).
3. If the shaft does not rotate or requires a lot of force, the compressor is faulty.

⚠️ Attention: Do not try to disassemble sealed compressor yourself! There is freon inside under pressure, and re-sealing at home is impossible.

FAQ: Answers to frequently asked questions