A sudden stop in the operation of the refrigerator or its inability to maintain the set temperature often indicates a malfunction of the main unit - the motor-compressor. It is this unit that is responsible for circulating the refrigerant in the system, creating the necessary pressure to cool the chambers. Before calling a technician or buying new equipment, it makes sense to carry out initial diagnostics yourself, using available tools.
The main device for such a test is multimeter (or tester), which allows you to measure the electrical resistance of the motor windings and check the integrity of the circuit. A compressor malfunction can be caused by a break in the internal wiring, an interturn short circuit, or a breakdown of insulation on the housing. Understanding these processes will help you accurately determine whether the unit can be restored or requires a complete replacement.
In this article we will analyze in detail the process of preparing, taking readings and interpreting measurement results. You will learn what values are considered normal for different types of engines and how to safely carry out diagnostics without damaging the equipment and ensuring your personal safety.
Safety measures and tool preparation
Working with electrical appliances requires strict adherence to electrical safety rules, since the voltage in the network poses a real threat to life. Before starting any manipulations, you must completely turn off the power to the refrigerator by removing the plug from the socket. Even if the device is not working, residual charges may remain in the control circuit, and accidental activation during disassembly will lead to a short circuit.
To carry out high-quality diagnostics, you will need a digital multimeter with the function of measuring resistance (Ohmmeter) and checking circuit integrity (continuity). You will also need screwdrivers to remove the protective cover at the bottom of the unit and, possibly, pliers to carefully remove the terminals. Make sure that the tester probes are in good condition and that the wire insulation is not damaged.
After disconnecting from the network, let the compressor cool down if it tried to start before. A hot engine may have altered resistance characteristics, resulting in incorrect readings. In addition, dust often accumulates in the compressor area, which is best removed with a dry cloth before opening the electrical compartment.
⚠️ Attention: Never touch exposed wires or compressor terminals if the refrigerator is connected to an electrical outlet. The resistance test is carried out exclusively on completely de-energized equipment.
Access to the electrical part of the compressor
The compressor is usually located in a niche on the back wall of the refrigerator in the lower part. To gain access to the contact group, you must remove the protective metal or plastic casing. In some models Indesit or Atlant the casing is secured with latches that need to be carefully pressed out, while in technology Bosch or LG screw connections can be used.
After removing the cover you will see the compressor itself - black metal a cylinder to which a bundle of wires fits. Directly on the motor housing or next to it there is a start-up relay and a capacitor (if it is external). It is the terminals coming out of the compressor housing and entering the relay that we have to call.
Carefully remove the plastic box with the start relay and the protective device. Below it you will see three contacts coming out of the sealed motor housing. They can be arranged in a triangle or in a row. It is important not to confuse them with the contacts of the relay itself; we are only interested in the output from the motor “pot”.
☑️ Preparation for diagnostics
Search for contacts and winding diagram
Three pins coming out of compressor, represent the conclusions of three windings: starting, operating and common points. In order to take measurements correctly, it is necessary to understand which pin is responsible for what, although this is not always critical for the initial diagnosis of integrity. Typically, the contacts are marked with letters or arranged in a certain geometric sequence.
In most modern models, the arrangement of the contacts is as follows: the top two pins are the starting and working windings, and the bottom (or central, if they are in a row) is the common terminal. However, relying only on visual arrangement is dangerous, since manufacturers Whirlpool, Haier and Electrolux may use different layout standards.
The most reliable method of identification is to look for markings on the relay body or in the technical documentation. If the marking is erased, you can focus on the resistance: between the working and common windings it is minimal, between the starting and common windings it is average, and between the working and starting windings (through the common) it is total. But first you need to make sure that the windings “ring” at all.
Color coding of wires
In some relay models, the wires to the compressor are color coded: red - starting winding, green or white - working, black or yellow - common wire. However, do not rely blindly on the color, since the wires may have been replaced during previous repairs.
Checking the windings for opens and short circuits
We move on to the most important stage - measuring the resistance. Switch the multimeter to resistance measurement mode (limit 2 kOhm or 20 kOhm). First, check the device for serviceability by connecting the probes to each other: it should show zero or a value close to it.
Attach the probes to the pairs of contacts on the compressor. You need to get three readings:
1. Between the first and second contact.
2. Between the second and third contact.
3. Between the first and third contacts.
If the display shows one (infinity) in all positions of the probes, it means there is an accident in the windings break. This means that the internal circuit is broken and no current flows. A compressor with a broken winding cannot be repaired at home and requires replacement. If the resistance is close to zero in all cases, this indicates interturn short circuitwhich is also a fatal malfunction.
The situation is considered normal when you see specific resistance values, and they differ between pairs of contacts. For example, there may be 20 Ohms between the common and working terminals, 50 Ohms between the common and starting terminals, and the sum of these values (70 Ohms) between the working and starting terminals. This picture indicates that the electrical part is intact.
Diagnostics of breakdown on the housing
Even if the windings are intact, the compressor may be dangerous or faulty due to breakdown of insulation on the housing. This is a situation where the phase or neutral is in contact with the metal body of the motor. The test is carried out in the continuity mode or resistance measurement at the maximum limit (Megaohms).
Apply one multimeter probe to any of the three contacts of the compressor, and the second to a place on the motor body that has been cleared of paint (you can use a metal tube or a specially cleaned area of the cylinder). The device should not react: the arrow should not deviate, and the digital indicator should show infinity.
If you hear a squeak or see low resistance values, it means the insulation is broken. Operate such a refrigerator strictly prohibitedas this may result in an electric shock if you touch the metal parts of the unit. Breakdown often occurs due to overheating, aging of varnish insulation or moisture getting inside the windings.
| Measurement type | Normal reading | Fault indication | Diagnosis |
|---|---|---|---|
| Winding resistance | 10 - 150 Ohm (specific number) | Unit (1) or 0 | Open or short short circuit |
| Breakdown to housing | Infinity (OL) | Any resistance value | Insulation breakdown (dangerous!) |
| Circuit integrity | There is a sound signal | There is no sound signal | Open circuit |
| Resistance between terminals | R1 + R2 = R3 | Chaotic values | Structure violation windings |
Interpretation of results and table of values
The data obtained must be correctly deciphered. Different manufacturers use motors with different parameters. For example, compressors Danfoss (now Secop) often have higher winding resistance compared to motors Aspera or LG. It is important not only the presence of resistance, but also its ratio.
If the resistance of the starting winding is significantly higher than the working winding (2-3 times), this is normal. However, if the difference is too great or the resistances are almost equal, this may indicate a violation of the turns. It is better to look for exact data on a specific model in technical reference books, but the general principle remains unchanged: the circuit must be closed, but not short.
It is also worth considering the engine temperature. A cold motor will show less resistance than a hot one. If you take measurements immediately after a startup attempt, the readings may be overestimated. Let the equipment sit for several hours to cool down and level the readings.
⚠️ Attention: If the multimeter shows a “short circuit” (close to 0 ohms) between any two contacts, this means that the windings have burned out and are shorted together. Starting such a compressor will lead to knocking out plugs or burning out the wiring in the house.
Frequent errors in diagnostics
Beginners often make mistakes that lead to false conclusions. One of the most common is an attempt to ring the compressor without removing the start relay. In this case, you measure the resistance not of the windings, but of the insides of the relay, capacitor or thermocouples, which gives an incorrect picture.
Another error is dirty or oxidized contacts. If there are oxides on the compressor pins or relay terminals, the resistance will jump. Before measuring, it is recommended to carefully clean the contacts with fine sandpaper or a file to ensure reliable contact with the probes.
Do not ignore the condition of the multimeter itself. A dead battery in a device can produce a large error or show a break where there is none. Always check the functionality of the tester on a known working circuit before starting work.
When the compressor is working, but does not work
It happens so that the tester shows ideal winding resistance, no breakdown to the housing, but the refrigerator still does not turn on or hums, but does not start. In this case, the problem may lie not in the motor itself, but in the auxiliary elements.
Most often it fails start relay. This device supplies an impulse to the starting winding to start the engine. If the relay is stuck or burnt out, the compressor will hum while trying to start, but the shaft will not rotate. Also, the cause may be a faulty thermostat or electronic control module that simply does not send a start command.
In rare cases, a so-called “wedge” of the compressor occurs - mechanical jamming of the piston group. The engine is electrically fine, but physically cannot turn over. Attempts to start such a unit lead to strong humming and heating, after which the thermal protection is triggered.
Is it possible to check the compressor without multimeter?
Indirectly - yes. If, when connected to the network, the compressor hums for 5-10 seconds and clicks (the protection is triggered), and then silence, and so on in a circle, this is a sign of a malfunction. However, it is impossible to determine exactly what it is (break, short circuit or breakdown) without a device. You can also try to apply voltage directly (bypassing the relay) for a short time, but this is dangerous and requires experience.
What resistance should be between the contacts?
There is no exact single value. For low-power compressors (up to 150 W), the operating winding resistance is 20-40 Ohms, the starting winding resistance is 40-80 Ohms. For powerful models, the values may be lower (10-20 Ohms). The main rule: the sum of the resistances of the two windings relative to a common point must be equal to the resistance between the other two contacts.
What to do if a breakdown is detected on the housing?
You cannot operate such a refrigerator - it is life-threatening. The compressor needs to be replaced. In some cases (very rare), rewinding the motor in a specialized workshop helps, but the cost of such work often exceeds the price of a new compressor.
Why does the multimeter show infinity?
The infinity indicator (usually the number 1 on the left of the display or the inscription OL) means that the circuit is open. If you measure between the winding contacts and see infinity everywhere, it means there is a wire break inside the motor. It is impossible to restore such a compressor.