Diagnostics of a refrigerator compressor begins with understanding its internal electrical circuit, where the stator windings play a key role. When a motor fails or the starting system fails, the first thing the technician must do is determine which part of the electric motor has failed. Often the problem lies in a break or interturn short circuit, and in order to identify this, it is necessary to clearly distinguish the purpose of the terminals.
In modern single-phase asynchronous motors used in household refrigerators, there are usually three terminals coming from the windings. Two of them relate to the working circuit, which ensures the main rotation of the rotor, and the third - to the starting circuit, which creates the starting torque. Incorrect identification of these contacts when connecting can lead to instantaneous burnout of the winding or overheating of the motor.
In this guide, we will examine in detail methods for identifying pins using a multimeter, visual analysis and resistance measurements. You will learn how to distinguish working winding from the launcher, without making fatal errors when assembling the circuit. Knowledge of these nuances is necessary for independent repairs or high-quality diagnostics before calling a specialist.
The design of the stator and the role of the windings in starting the motor
The compressor electric motor is a complex system where the stator contains two main windings with different physical characteristics. Working winding (or main) occupies most of the stator slots and is made of wire of a larger cross-section. It is this that consumes the main part of the energy during operation of the refrigerator and maintains the rated speed of rotation of the rotor.
The second component - starting winding - has a smaller number of turns, but is often made with thinner wire or is located so as to create a phase shift. Its task is to create an initial magnetic field that will “spin” the rotor to a certain speed. After reaching a speed of about 75% of the rated speed, the starting circuit should be turned off using the starting relay.
If these windings are mixed up when connected, the engine may hum, but not start, or start in the opposite direction (which is unacceptable for a refrigerator compressor and leads to valve failure). Therefore, understanding the physics of the process and a clear distinction between main and starting circuits is critically important.
⚠️ Attention: Attempting to start the compressor with an incorrectly connected starting circuit winding as a working one will lead to a sharp jump in current and overheating of the insulation in a matter of seconds.
The design of the windings may vary depending on the compressor manufacturer, be it Atlant, LG or Danfoss. However, the principle of separation into high-resistance (starting) and low-resistance (working) circuits remains universal for most household models. In some modern inverter models, the circuit may be more complex, but in classic linear compressors the rule of two windings applies without exception.
Visual identification and marking of contacts
The first stage of diagnosis is an external inspection of the compressor contact group. On many models, the terminals have letter markings printed directly on the contact pins or on a plastic block. Latin letters are usually used: C (Common) - common wire, R (Run) - working winding, and S (Start) - starting winding.
If the markings are erased or missing, you can rely on the color coding of the wires, coming from the start relay. Although standards may vary from plant to plant, there is generally accepted practice. For example, in compressors Atlant the common wire is often green with a yellow stripe, the working wire is red, and the starting wire is brown or black. Manufacturers LG and Samsung colors may vary, so relying only on them is risky.
- 🔴 Red wire - most often connected to the output of the working winding.
- 🟤 Brown or black - usually goes to the starting winding winding.
- 🟢 Green or green with yellow - is often a common conclusion.
- 🔵 Blue - in some circuits may indicate the starting circuit.
However, the visual method does not provide a 100% guarantee, since repairmen could have previously changed the wires, and the factory markings could fade. Therefore, after the initial inspection, you should definitely proceed to an instrumental check. The only reliable way to determine the purpose of the windings is to measure the active resistance between the terminals.
Methodology for measuring resistance with a multimeter
To carry out an accurate diagnosis, you will need a digital multimeter switched to the resistance measurement mode (Ohm). Before starting work, make sure that the refrigerator is disconnected from the power supply and the starting relay is removed from the contact group. Measurements are taken between three terminals that form a triangle.
The measurement process consists of checking all contacts in pairs. You need to get three resistance values: between the first and second terminals, between the second and third, and between the first and third. Write down the results, since it is the ratio of these numbers that will allow you to identify the windings. data-i="88">Digital multimeter working And launcher windings
The logic of the definition is simple: the greatest resistance will be between the ends of the starting and working windings (that is, measuring through a common point, we get sum of resistances). The working winding always shows the least resistance, since it is wound with a thicker wire and has fewer turns. The average value corresponds to the starting winding.
☑️ Compressor testing algorithm
Normal resistance values for household refrigerators vary in the range from 10 to 40 Ohms for starting and from 5 to 15 Ohms for operating windings, depending on the motor power.
Analysis of the obtained data and correspondence table
After taking measurements, it is necessary to systematize the data. Imagine you have three terminals: A, B and C. You measure the resistance between A-B, B-C and A-C. One of these values will be the sum of the other two (or close to it, taking into account the error). This is the resistance between the free ends of the working and starting windings.
For ease of understanding the distribution of resistance, consider an approximate table of values for a typical compressor with a power of about 1/5 hp. (for example, series models SC or NL). The numbers may differ, but the proportions remain the same.
| Pair of measured contacts | Circuit type | Expected resistance (Ohm) | Characteristics |
|---|---|---|---|
| Pin 1 - Pin 2 | Working winding | 12.5 Ohm | Lowest value |
| Pin 2 - Pin 3 | Start winding | 28.0 Ohm | Average value |
| Pin 1 - Pin 3 | Total (Operating + Starting) | 40.5 Ohm | Highest value |
Analyzing the table, we see that contact No. 2 is common, since it is involved in measuring the smallest (working) and average (starting) resistance. Therefore, pair 1-2 is working winding, and pair 2-3 is starting. Contact No. 1 will be the working terminal, No. 3 will be the starting terminal, and No. 2 will be the common one.
⚠️ Attention: If the sum of the resistances of two smaller values is very different from the third (more than 10-15%), this may indicate turn-to-turn short circuit in one of the windings.
This analytical approach allows you to accurately determine the purpose of contacts even on compressors without markings. The main thing is to carefully record the readings of the device and not confuse the conclusions. An error in identifying the common wire will result in you applying 220 volts to the wrong winding, which is guaranteed to damage the motor.
Connection diagram and service check
Once the pins have been identified, you need to correctly assemble the circuit for a test run or installing a new relay. Common wire connects to one phase of the network (or through protection), working winding - to the second phase, and starting - through a starting relay (capacitor or posistor). In older models, the relay can be electromagnetic, in new ones it is more often posistor.
When assembling, make sure that the contacts fit tightly to the compressor terminals. Oxidized or loose contacts can cause sparking and heating, which is harmful to the plastic relay housing. To check the continuity of the circuit, you can use the “continuity” function on the multimeter, which gives a sound signal when the resistance is low.
The nuances of the operation of a posistor relay
A posistor is a thermistor that, when cold, has low resistance and passes current to the starting winding. When heated by current, its resistance increases sharply, actually opening the circuit of the starting winding. If the compressor hums but does not start, it is often the posistor that is to blame, and not the motor itself.
If, when testing, the multimeter shows “infinity” (one in the most significant digit or OL) between any two terminals that should be connected by a winding, then there is an open circuit. This may be a consequence of a burnt-out wire inside the stator or a burnt-out contact inside the compressor housing. In the event of a break, repairing the compressor at home is impossible - the unit must be replaced.
It is also worth checking for a breakdown in the housing. Switch the multimeter to resistance measurement mode at the maximum limit (Megaohms) or diode test mode. Touch any terminal with one probe, and the metal body of the compressor with the other (clean a small area of paint for contact). The device should not show any conductivity.
Typical faults and problem diagnosis
The most common problem is an interturn short circuit in working winding. In this case, the resistance will be lower than normal, and the current consumption at startup will be significantly higher. The compressor may turn on, run for a few minutes, and then turn off via a thermal relay due to overheating. It is difficult to determine this only by continuity; often it is necessary to measure the current consumption with an ammeter.
Another common situation is a breakdown of the insulation of the starting winding. Because it only works for a short period of time, its insulation can degrade due to age or moisture. When such a compressor is turned on, the circuit breaker in the panel may be knocked out or the plug fuse may burn out.
- 🔥 The compressor hums and turns off - probably the mechanical part is jammed or the start relay is faulty.
- 📉 The resistance of the windings is very different from the passport data - a sign interturn short circuit.
- ⚡ A breakdown to the housing is fatal and requires immediate replacement of the compressor.
⚠️ Attention: Technical characteristics of compressors may vary depending on the year of manufacture and the specific modification. Always check the data obtained with the manufacturer’s official documentation or service manual for your refrigerator model.
Diagnostics must be comprehensive. If the electrical parameters of the windings are normal, but the refrigerator does not freeze, the problem may be a freon leak or a clogged capillary tube. However, checking the windings is the first and mandatory step to rule out electrical causes of failure.
Frequently asked questions (FAQ)
Is it possible to start a compressor without a starting relay?
Technically, you can start the motor by briefly applying voltage to the starting winding manually, but this is extremely dangerous and is not recommended for non-professionals. Without a relay, the starting winding will not turn off, it will quickly overheat and burn out. For diagnostics, a button or a special device is used, but long-term operation without a relay is impossible.
What to do if the resistance of the starting and operating windings is the same?
In classic asynchronous motors of refrigerators, the resistance of the windings should be different (the operating winding is always less). If the values are identical, this may indicate a specific engine design (rare) or, more likely, a faulty meter, poor probe contact, or an internal short that has leveled the resistance.
How to determine where the common wire is if there is no marking?
The common wire is at the intersection of the circuits with the lowest and average resistance. If you measured three pairs of contacts, find the pair with the maximum resistance - these are the ends of the working and starting windings. The third, remaining wire is the common one (Common).
Why does the compressor hum, but does not start, although the windings are intact?
If the windings show normal resistance, the reason is most likely in the starting relay (the contacts are stuck or the posistor is burned out), in the capacitor (if there is one in the circuit) or in mechanical jamming compressor piston group. Low voltage in the network is also possible.