Starting winding of the refrigerator compressor: how to determine correctly and not confuse with working

When the refrigerator suddenly stops freezing, and the compressor motor only hums but does not start, the problem often lies in starting winding. This malfunction occurs both in old Saratov and Birusaand in modern models LG or Samsung. But before you run for a new relay or compressor, you need to make sure that it is the starting winding that is to blame - and not the working winding, not thermal protection or mechanical blocking.

The main difficulty for beginners is that the windings look the same externally, and mixing them up when checking means either a false diagnosis or the risk of burning the compressor when incorrect connection. In this article we will analyze 4 reliable methods for determining the starting winding: from visual inspection to measurements with a multimeter, and also tell you what hidden “traps” await when testing compressors with different connection schemes.

What is a starting winding and why is it needed

A refrigerator compressor is an asynchronous electric motor that cannot start on its own without an additional “push”. This is exactly why it exists starting winding. It creates a rotating magnetic field necessary for the initial acceleration of the rotor. As soon as the engine picks up speed, the starting winding is switched off through start-protection relay, and further operation is supported only by working winding.

Why is this important for diagnostics? If the start winding is burned out or shorted, the compressor will hum but will not be able to start. If the problem is in the working winding, the motor will either not turn on at all, or will work with overheating and frequent shutdowns. Therefore the first step of repair is to accurately identify which winding is faulty.

• 🔧 The starting winding - temporary, it works only at startup (1-3 seconds). It has less resistance than the working one.
• 🔄 Working winding is constant, supports the rotation of the rotor. The resistance is higher, the current consumption is lower.
• ⚡ Common point is the junction of both windings inside the compressor. One of the power pins is connected to it.

⚠️ Attention: In compressors with built-in thermistor (for example, Danfoss or Secop) the starting winding may have an additional protective element. When checked with a multimeter, this will give a false “infinity” resistance - do not confuse it with a break!

External signs of a malfunction of the starting winding

Before disassembling the compressor, pay attention to the behavior of the refrigerator. Typical symptoms of a problem with the starting winding:

• 🔊 The compressor hums, but does not start (the relay clicks, after which the motor is silent).
• 🔥 The relay overheats and turns off the power 5-10 seconds after the start attempt.
• ⚡ When turned on in network, the machine in the panel is triggered (short circuit in the winding).
• ❄️ The refrigerator does not freeze, but the light inside is on (there is power, but the compressor does not work).

If at least one of these signs is present, the probability of a problem with the starting winding is ~70%. However an accurate diagnosis can only be made after checking the resistance. For example, similar symptoms are given by a jammed motor or a faulty relay - so you can’t do without a tester.

Connection diagram of the compressor windings

To properly check the windings, you need to understand how they are connected inside the compressor. Most models (for example, Atlant, Indesit, Beko) use a circuit with three terminals:

1. Common terminal (C) —connection of the starting and working windings.
2. Output of the working winding (R) —connects to the network via a relay.
3. Output of the starting winding (S) —connects to the network via a starting capacitor (if any) and a relay.

Visually the pins are marked as follows:

• 🔹 C (Common) - general.
• 🔹 S (Start) - starting.
• 🔹 R (Run) - working.

If your compressor only two terminals (for example, for some models Whirlpool, this means that the starting winding is constantly connected through a capacitor (circuit PSC). In this case, the diagnosis becomes more complicated - you will need to check the capacitance of the capacitor.

Step-by-step instructions: how to determine the starting winding with a multimeter

To check, you will need any digital multimeter (for example, DT-830B or Mastech MY64). Follow the algorithm:

Disconnect the refrigerator from the network and discharge the capacitor (if any)

Remove the start-up relay from the compressor

Clean the compressor terminals from oxidation (with sandpaper or a file)

Check the multimeter for functionality (short circuit the probes, it should show 0 Ohm)-->

1. Measure the resistance between all pairs of terminals:

   • 🔧 C-S (start winding) - usually 5–20 Ohm.
   • 🔧 C-R (working winding) - usually 10–40 Ohm.
   • 🔧 S-R - the sum of the two previous values.

If at least one of the resistances is equal 0 Ohm (short circuit) or ∞ (open), the winding is faulty.

Define the common terminal (C):

This is the terminal, the resistance between which and the other two gives smallest i average values. For example, if:

• Pin1-Pin2 = 15 Ohm,
• Pin1-Pin3 = 30 Ohm,
• Pin2-Pin3 = 45 Ohm,

then Pin1 — common (C), Pin2 — starting (S), Pin3 —working (R).

• Check the insulation on the case:

  Set the multimeter to mode megohmmeter (200 MOhm) and measure the resistance between each terminal and the metal housing of the compressor. The norm is more than 2 MOhm. If it is less, the winding is “broken” to the housing, the compressor needs to be replaced.

⚠️ Attention: B compressors with built-in thermal protection (for example, Embraco) when the windings heat up, the resistance may temporarily change. If the test gives unstable results, let the compressor cool for 30-60 minutes and repeat the measurements.

What to do if the winding resistances are the same?

If the resistances C-S and C-R are the same (for example, 15 Ohms), this may mean:

1) Compressor with symmetrical windings (rare, but occurs in some Mitsubishi).

2) Break in one of the windings (check S-R -if it is not equal to the sum, there is a break).

3) Error in measurements (recheck the probe contacts).

In this case, additional diagnostics will be required by connecting the compressor to the network via a ballast lamp (60–100 W).

Visual differences in the windings (if the compressor is disassembled)

If you have access to the insides of the compressor (for example, during complete disassembly for repair), the starting winding can be determined by the following characteristics:

• 🎨 Wire color: often the starting winding is wound with wire darker shade (brown, black), and the working winding is wound with light wire (red, orange). However, this is not a rule, but only a trend!
• 📏 Wire thickness: the starting winding is usually thinner, as it is designed for short-term operation with high current.
• 🔍 Location: in most models the starting winding is closer to the top of the stator, and the working winding is closer to the bottom.
• 🧲 Magnetic field: if you bring the compass to the windings when connecting the power for a short time (only for experienced ones!), the launcher will create a stronger field due to the higher current.

Important: Disassembling the compressor at home is highly not recommended without special tools and skills. It is almost impossible to restore the tightness of the housing after assembly, which will lead to freon leakage and breakdown of the refrigerator. Visual inspection is only relevant for professionals or when disposing of the compressor.

Typical errors when determining the starting winding

Even experienced technicians sometimes make mistakes that lead to false diagnosis. Here are the most common ones:

1. The common terminal is confused with the starting terminal:

   If you confuse C and S, when connected, the compressor will try to start “in the opposite direction,” which will lead to water hammer and failure. Always double-check the resistance!

2. Ignore the capacitor:

   In circuits with starting capacitor (for example, Hitachi or Toshiba) its capacitance directly affects the winding resistance. If the capacitor is faulty, the starting winding may “ring” as a working one.

3. Temperature is not taken into account:

   The resistance of the windings depends on temperature. If the compressor is hot, the multimeter reading may be 10-20% high. Let it cool before checking.

4. Check the windings “on weight”:

   When taking measurements, the compressor should lie stable, and the probes of the multimeter should fit snugly to the terminals. A bad contact will give false readings.

What to do if the starting winding is faulty

If diagnostics have confirmed a problem with the starting winding, you have three options:

1. Replacing the starting protection relay:

   Sometimes the winding “dies” due to a faulty relay that does not turn it off in time. The cost of a new relay is from 500 to 2000 rubles (for example, RTK-X or Danfoss 103N0016). Suitable if the winding is intact, but the compressor does not start.

2. Winding repair:

   Theoretically, it is possible to rewind the winding, but in practice this is unprofitable: the cost of work exceeds the price of a new compressor, and the warranty no to the result. Relevant only for rare or vintage models.

3. Replacing the compressor:

   The most reliable option. A new compressor (for example, Embraco EGX90HLC or Secop SC10ML) will cost 4,000–10,000 rubles, plus 1,500–3,000 for refilling with freon. When replacing, be sure to:

   • 🔧 Use a similar model according to the power and type of freon.
   • 🔧 Replace filter-drier and vacuum system.
   • 🔧 Check integrity of tubes for microcracks.

⚠️ Attention: In compressors c inverter control (for example, LG Linear Compressor) there is no starting winding in the classical sense - an electronic starting circuit is used there. Diagnostics of such models requires an oscilloscope and knowledge of the specifics of inverters.

FAQ: Frequently asked questions about the starting winding

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

No. Without a starting winding (or its analogue, for example, an electronic unit), the compressor will not be able to overcome the initial resistance and gain speed. At best, it will hum, at worst, the working winding will burn out from overload.

Why is the resistance of the starting winding less than the working one?

The starting winding is designed for short-term, but high currentnecessary to create a strong magnetic field at startup. Lower resistance allows more current to pass than through the working winding.

How to check the starting capacitor?

Disconnect the capacitor from the circuit and check it with a multimeter in capacitance measurement mode (200 µF). The normal value should correspond to the markings on the case (for example, 40 µF ±5%). Also check the resistance: when connecting the probes to the terminals of the capacitor, the resistance should gradually increase from 0 to ∞ (charging). If it shows 0 —a short circuit, if ∞ —a break.

What happens if you mix up the starting and operating windings when connecting?

If you connect the compressor “back to front” (change in some places S and R, the following will happen:

1. The compressor will try to start in the opposite direction (which is not critical for most models).
2. The starting winding will work constantly, which will lead to its overheating and failure within 5–30 minutes.
3. The thermal protection or circuit breaker in the panel may be triggered.

The situation can be corrected by swapping the wires, but if the winding is already overheated, the compressor will need to be replaced.

How to determine the starting winding in a compressor with two conclusions?

In compressors with two terminals (diagram PSC), the starting winding is connected permanently through a capacitor. To check it:

1. Disconnect the capacitor from the circuit.
2. Measure the resistance between the terminals of the compressor - it should be equal to the resistance working winding (usually 10-40 Ohms).
3. Check the resistance of the capacitor (must correspond to the marking).

If there is resistance between the terminals 0 Ohm or ∞, the compressor is faulty.