Diagnosis of refrigeration equipment malfunctions often begins with checking the electrical part of the motor. In situations where the compressor hums, but does not start, or is completely silent, the first step is to ensure the integrity of the stator windings. Determination of the starting and operating windings is a critical step, since incorrect connection of the terminals can lead to instant combustion of the engine or failure of the starting relay.
Modern single-phase motors installed in household refrigerators have a complex internal configuration hidden in a sealed casing. Only three external outputs are available, the markings of which may fade over time, lose readability or be completely absent on older models. Understanding the physics of the process and the ability to use measuring instruments will allow you to independently carry out initial diagnostics without contacting a service center.
In this article we will analyze in detail the algorithm of actions, which will help you accurately identify each contact. We will look at methods for measuring resistance, visual inspection and logical analysis of the connection diagram. The working winding always has less active resistance compared to the starting winding, which is a fundamental law of electrical engineering for such motors.
The operating principle and design of the stator windings
To successfully find the necessary contacts, you need to understand how they work asynchronous refrigerator motor. The motor stator contains two main windings wound with copper wire of different diameters and cross-sections. Working (main) winding occupies most of the slots and is designed to create the main rotating magnetic field during compressor operation.
Second winding, called starting, has a smaller number of turns, but is often made with wire with a smaller cross-section, which affects its electrical characteristics. It comes into operation only for a short time at the moment of startup, creating the necessary phase shift for the starting torque to occur. After the rotor accelerates, this circuit is opened by the starting relay or electronic module.
The third pin that you will find on the terminal block is general. It is to this that the phase power wire is supplied, and the current distribution between the working and starting windings occurs inside the engine, depending on the relay connection diagram. Without the correct determination of the common output, all further diagnostics are meaningless.
⚠️ Attention: Never apply 220 volts to the compressor contacts at random for testing. An attempt to apply a phase to the starting winding as a working one will lead to overheating and breakdown of the insulation in a matter of seconds.
Required tools and safety measures
Before starting any work with the electrical components of the refrigerator, you must strictly follow the safety rules. The main tool you will need is a multimeter (tester) capable of measuring resistance in the range from 0 to 200 ohms. It is advisable to use a device with an audio test to quickly check the integrity of the circuits.
You will also need tools to dismantle the compressor casing and remove the protective cover of the terminal box. Usually this is a set of screwdrivers and side cutters. Do not forget to prepare electrical tape or cambrics to mark the wires after checking, since it is very easy to mix them up during assembly.
Work should only be carried out with the refrigerator completely disconnected from the network. Unplug the plug from the socket and make sure there is no residual voltage at the terminals. If the compressor has just been running, let it cool down so as not to get burned and not to distort the resistance readings due to heating of the copper.
☑️ Preparation for diagnostics
Visual identification and marking of terminals
The first stage of the search is a careful inspection of the terminal block located in the bottom compressor parts. On many modern models, such as Atlant, Indesit or LG, the terminals may have letter markings printed directly on the plastic case or on metal contacts.
The standard marking looks like this: letter R (or Run) denotes the working winding, the letter S (or Start) - the starting winding. The common contact may be designated by the letter C (Common) or simply not have a designation if it is located separately. Some circuits use marking L for the power line.
However, you cannot rely on letters alone. Over time, the plastic fades and the markings are erased by vibration and moisture. On old Soviet compressors HC or DH there may be no markings at all. In such cases, the visual method provides only preliminary information that requires mandatory instrumental verification.
Color marking of wires
On some compressors, the colors of the wires going from the relay to the terminals can tell appointment. The red or brown wire often goes to the working winding, and the blue or black wire to the starting winding. However, manufacturers do not always adhere to a single standard, so colors should be considered only as an auxiliary sign.
Method of measuring resistance with a multimeter
The most reliable way to find the starting and operating windings is to measure the resistance between pairs of contacts. Set the multimeter to resistance measurement mode (limit 200 ohms). First, find the common wire: measure the resistance between all three pairs of contacts.
The pair of contacts shown highest resistanceare the ends of the starting and working windings connected in series. The third, remaining contact is common terminal. Remember it or immediately mark it with a marker, since we will start from it in further measurements.
Now measure the resistance between the common contact and each of the two remaining ones. The contact that shows lower resistance (usually in the range of 10-25 Ohms) refers to the working winding. The contact with high resistance (usually 30-60 Ohms) is the starting winding.
| Measurement parameter | Working winding (Run) | Starting winding (Start) | Common wire (Common) |
|---|---|---|---|
| Resistance (Ohm) | Low (10-25 Ohm) | High (30-60 Ohm) | Not measured separately |
| Wire cross-section | Thick | Thin | Total |
| Operating mode | Permanently | Short-term | Permanently |
| Location in grooves | Basic | Additional | - |
Typical resistance values for different brands
Resistance values can vary significantly depending on the power of the compressor and the manufacturer. For example, low-power compressors for minibars may have higher winding resistance than powerful units for large refrigerators. Below are approximate data.
Compressors Danfoss/Secop are characterized by working winding values in the region of 15-20 Ohms, and starting windings - about 40 Ohms. Units Embraco often have slightly lower values: 10-15 Ohms for working and 25-35 Ohms for starting. Chinese analogues may show a range of 10-30% from these values.
It is important to take into account the temperature of the windings when taking measurements. Copper has a positive temperature coefficient of resistance. If the engine is hot, the multimeter reading will be higher than the actual cold reading. For accurate diagnostics, it is better to take measurements on a cooled compressor.
Analysis of the connection diagram and starting relay
Understanding how the windings are connected to the starting relay relay helps to finally verify the correctness of the conclusions. The start relay is attached directly to the compressor terminals. The relay contacts close the starting winding circuit only at the moment of start.
If you trace the path of the wires from the relay, you can see that one wire goes directly to one of the compressor contacts (usually the working winding or common), and the other is switched through the relay contacts. In circuits with capacitor starting, the capacitor is connected in series with the starting winding.
Sometimes an electrical diagram is printed on the terminal box cover itself or on the relay body. It may be erased, but upon careful examination with a magnifying glass, the symbols can be distinguished. The connection point of two windings inside the engine is always connected to a common contact, to which the network zero is connected.
⚠️ Attention: If, when testing, the multimeter shows a resistance close to zero (short circuit) or infinity (open) between any two contacts, the compressor is faulty. Operation of such a motor is prohibited.
Frequent errors and troubleshooting
One of the common mistakes is confusion between the common wire and the phase wire. Beginners often assume that the common wire is the one in the geometric middle, but the arrangement of contacts on the triangular block may vary between models. Always rely on resistance measurements, not geometry.
Another problem is contact oxidation. If the terminals are covered with oxides, the multimeter may show incorrect, overestimated resistance. Before taking measurements, it is recommended to carefully clean the contacts with fine sandpaper or a file without damaging the copper wires.
It is also worth mentioning the breakdown to the housing. Be sure to check the resistance between any of the three contacts and the copper tube of the compressor (after cleaning the contact area with a probe). The device should show infinity. Any resistance value indicates an insulation breakdown and a risk of electric shock.
Final recommendations for assembly
After you have managed to find the starting and operating windings and make sure that the engine is working properly, you can begin assembly. Install the start relay exactly according to the orientation (usually up arrow). Incorrect installation of the relay may cause it to stick or fail to start.
Attach the protective cover and connect the power wires. When you turn it on for the first time after repair, listen carefully to the sound of the compressor. A smooth hum without metallic knocks or clicks indicates that the work was performed correctly.
Regular diagnostics of the electrical part of the refrigerator allows you to extend the life of the equipment. Knowing how to find the starting and running windings is a basic skill for any home mechanic repairing household appliances.
What to do if the winding resistances are almost the same?
In rare cases, especially on older or specific engine models, the resistances of the starting and running windings can be very close (1-3 Ohm difference). In this case, be guided by the thickness of the wire, if you can look inside the terminals, or try running the compressor through a circuit with a capacitor, monitoring the current consumption with a current clamp. The current on the working winding should be stable, and on the starting winding it should increase sharply at the moment of start and fall.
Is it possible to start a compressor without a starting relay?
You can start the engine for a short time by applying voltage to the working winding and briefly closing the starting winding circuit with a button. However, doing this is dangerous: without a relay, the starting winding may not turn off in time, which will lead to its burning. This method (“push”) is used only by experienced craftsmen to diagnose the wedge, but not for permanent work.
Why does the working winding heat up?
Excessive heating of the working winding may indicate an interturn short circuit, even if the resistance is normal. Also, the cause may be low voltage in the network, a malfunction of the thermostat (the compressor does not turn off) or insufficient ventilation of the condenser. If the winding heats unevenly or there is a burning smell, it is better to replace the compressor.