How to determine the starting winding of a refrigerator compressor
A compressor malfunction often confronts the refrigerator owner with a difficult choice: call a technician or try to diagnose the problem yourself. One of the key steps in checking the electrical part of the engine is the correct identification of the winding terminals. An error in the connection can lead to instant failure of an expensive unit or even a fire hazard, so theoretical preparation is critical here.
Inside the sealed motor casing, two main coils are hidden: working and starting. They have different electrical resistance, different wire diameters and perform different functions when starting the unit. Understanding the physical principles of operation of these elements will allow you to accurately identify the contacts on the block, even if the factory markings are erased or missing.
In this article we will analyze proven diagnostic methods that are used by professional service center technicians. You will learn how to prepare the tool, what multimeter readings are considered normal and what to pay special attention to when visually inspecting the wires coming out of the compressor housing.
The fundamental difference between the working and starting windings
The electric motor of a household refrigerator is an asynchronous single-phase unit that cannot start on its own without the external influence of a magnetic field. To create the initial torque, starting windingis used, which is activated only for a few seconds at the moment of start. After the rotor accelerates, it is turned off by a special relay, and further rotation is supported by the working winding.
Structurally, these coils are made differently to optimize their tasks. The starter is wound with a thinner wire and has a greater number of turns, which provides high active resistance. The working winding, on the contrary, is wound with a thick wire and has less resistance, since it consumes the main current during the entire operation cycle of the refrigerator.
It is the difference in resistance that is the main marker for diagnosis. If you connect power to the starting winding as a run winding, the motor will hum, get very hot, and quickly burn out due to overcurrent. Therefore, determining the ends of the windings is the first thing to do before any attempt to start.
⚠️ Attention: Never apply 220V voltage to the compressor contacts directly, bypassing the starting and protective relay, unless you have first rung the windings and made sure their integrity. This may result in a short circuit.
There is also the concept of a "common terminal", which is the connection point between two coils inside the motor. Correct identification of this contact is the key to successful assembly of the electrical circuit. In modern models, such as Indesit or LG, the circuit can be supplemented with a capacitor, which changes the nature of the current flow, but the basic principle of the difference in resistance remains unchanged.
Why does the starting winding burn out more often?-->
Necessary tools and preparation to diagnostics
Before proceeding with “opening” the electrical part, it is necessary to ensure safe working conditions. You will need a minimum set of tools that any home craftsman will have. The main device will be multimeter (tester), capable of measuring resistance in the range from 0 to 2000 Ohms.
To access the contact group, you will have to remove the back cover of the refrigerator and dismantle the compressor casing. Be prepared to work in confined spaces. You will also need pliers, insulating tape and, possibly, a needle file for cleaning oxidized contacts if the engine is old.
Pay special attention to safety. All manipulations with electrical circuits are carried out only with the refrigerator completely disconnected from the network. Unplug the cord from the outlet and make sure that there is no residual charge left on the capacitors (if they are in the circuit).
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Visual inspection of the wires coming out of the housing can give the first clue. Often (but not always!) the wires have different insulation colors or different thicknesses. However, you cannot rely only on color, since during previous repairs the wires could have been replaced or mixed up.
Method of testing contacts with a multimeter
The most reliable method of identification is to measure the resistance between pairs of contacts. The compressor block usually has three terminals arranged in a triangle. Your task is to ring them in pairs and write down the results. Switch the multimeter to resistance measurement mode (Ohm).
Touch any two contacts with the probes. If the device shows infinity (one in the most significant digit or “OL”), then there is a break between these terminals, and this is not the desired pair for one winding. If the device shows a specific value, for example, 25 Ohms, record this pair and values.
Repeat the procedure for other combinations. As a result, you will have three measurements. Two of them will show the resistance of individual windings, and the third will show the sum of resistances (resistance between the extreme terminals). The highest value will correspond to the sum of the resistances of the starting and working windings.
The action algorithm looks like this:
🔌 Measure the resistance between the top and left contacts.
⚡ Measure the resistance between the top and right contacts.
🔋 Measure the resistance between the left and right contacts.
📝 Compare the values obtained: the smaller is the working winding, the average is the starting winding, the largest is the sum.
📊 What device do you use for diagnostics?
Pointer tester Ts-20
Digital multimeter DT-830
Professional Fluke
I do not have a device
Other
Table of typical resistance values for different compressors
Resistance values may vary depending on engine power, manufacturer and year of manufacture. For example, compressors Atlant and Danfoss (now Secop) may have different characteristics. Below is a table with approximate data that will help you navigate the device readings.
Compressor type
Working winding resistance (Ohm)
Starting winding resistance (Ohm)
Total resistance (Ohm)
Low power (up to 100 W)
15 - 25
30 - 45
45 - 70
Medium power (100-150 W)
10 - 18
20 - 35
30 - 53
Powerful (inverter)
5 - 12
15 - 25
20 - 37
Old models (USSR)
20 - 30
40 - 60
60 - 90
Please note that the resistance of the starting winding is always 1.5–2 times higher than the working resistance. This is a physical pattern determined by the thickness of the copper. If your measurements show the opposite (the starting winding is less than the working one), it means that you made a mistake in identifying the pins or the motor has a non-standard circuit.
It is important to take into account the error of the device and the temperature of the engine. A cold engine will show less resistance than a hot one. If the values differ greatly from the tabulated ones (for example, they show 0 Ohm or are close to zero), this indicates an interturn short circuit.
⚠️ Attention: If the multimeter shows resistance between any of the terminals and the copper compressor housing (for breakdown), it is prohibited to operate such a unit. This means that the insulation has burned and the housing is energized, which is deadly.
Visual signs and terminal markings
Although electrical measurement is the most accurate method, visual clues should not be ignored. On many modern compressors, the contact group is marked with letters. Latin letters are usually used: C (Common) - general output, R (Run) or M (Main) - working winding, S (Start) - starting winding.
The location of the contacts on the block is also often standardized. If you look at the compressor from the contact side, the common point is often located at the top or bottom of the triangle, and the windings are on the sides. However, manufacturers Beko or Whirlpool they can use their own location standards, so you cannot blindly trust the geometry.
Pay attention to the thickness of the wires coming out of the “belly” of the compressor. The working winding wire is usually thicker, since the main working current flows through it. The starting wire is thinner. If you have the opportunity to carefully bend the insulation and compare the diameter of the cores, this will be an additional confirmation of your calculations.
Frequent errors and signs of winding malfunction
Even knowing the theory, beginners often make mistakes that lead to false conclusions. One of the most common is poor contact of the multimeter probes with the terminals. Oxides and carbon deposits create additional resistance, distorting the readings. Always clean the contacts to a shine before taking measurements.
Another mistake is ignoring ground readings. Many people forget to check whether the winding “rings” on the housing. Even if the resistance between the terminals is normal, a breakdown to the housing makes the compressor unsuitable for use in domestic conditions without serious rewinding, which is not economically feasible.
Signs of a malfunction that can be identified by dialing:
🔥 Open circuit: the device shows infinity on one of the windings (the engine hums, but not starts).
⚡ Short circuit: resistance is close to zero (knocks out the circuit breakers in the panel).
📉 Interturn short circuit: resistance is significantly lower than normal (the engine heats up and knocks out the thermal protection).
If you find an interturn short circuit, The compressor will most likely have to be replaced. Operation of such an engine will lead to constant activation of the thermal relay and spoilage of food in the refrigerator.
FAQ: Frequently asked diagnostic questions
Is it possible to start a compressor without a starting winding?
Theoretically, if you spin the shaft manually, the engine can only start on the working winding. However, in refrigerator conditions, where it is necessary to create pressure in the system, the torque of one working winding is not enough. The compressor will simply hum and heat up.
What to do if the winding resistances are the same?
In standard single-phase refrigerator compressors, the winding resistances cannot differ due to different wire thicknesses. If the device shows the same values, check the serviceability of the multimeter and the quality of the contact. In rare cases, this may indicate a specific two-phase motor, but for household appliances this is an exception.
Is it possible to swap the starting and operating windings when connecting?
It is absolutely not possible. If you apply operating voltage to the starting winding, it will burn out in a matter of seconds due to the high resistance and thin wire. If you mix up the terminals when assembling the circuit, the engine will not start or will operate in emergency mode.
Does the brand of the refrigerator affect the location of the terminals?
Yes, manufacturers use different standards. For compressors Atlant the circuit may differ from Samsung. Therefore, never rely solely on the color of the wires or their position in the past. Always double-check the findings with a multimeter for each specific motor.