A sudden stop of the refrigerator is always stressful, because food supplies are at risk. Often the cause of a breakdown is a failure compressor, which is the heart of the entire cooling system. Before calling a technician or buying new equipment, it makes sense to carry out initial diagnostics yourself, using available tools.
To check the electrical part of the engine, you will need a regular digital multimeter. This device will allow you to measure the resistance of the windings and determine the integrity of the circuit, which is the first step in identifying a malfunction. In this article, we will analyze an algorithm of actions that will help you understand whether the motor is alive or it’s time to change it.
Remember that any work with electrical appliances requires compliance with safety precautions. Before starting any manipulations, it is necessary to completely de-energize the unit by removing the plug from the socket. Ignoring this rule may result in electric shock or damage to the electronics of the refrigerator.
Preparatory steps and access to the compressor
The first step is to gain physical access to the motor, which is usually located in the lower rear part of the refrigerator. You will need to move the refrigerator away from the wall, allowing easy access to the back panel. In some models, it may be necessary to remove the protective cover secured with screws or plastic latches.
After removing the casing, you will see a cylindrical black tank - this is the compressor, to the bottom of which a start-up relay and thermostat fit. Before touching any contacts, make sure that the device is completely unplugged for at least 10-15 minutes to allow the capacitors to discharge.
⚠️ Attention: Do not start testing if traces of oil, burning, or melted insulation are visible on the compressor or wires. In such cases, a visual defect often indicates a breakdown that requires replacing the unit without further measurements.
To work, you will need a multimeter with a resistance measurement function (Ohm) and continuity tests. Make sure that the probes of the device are in good condition and that the battery in the tester is charged, since measurement errors can lead to an incorrect diagnosis.
Carefully remove the plastic box from the terminal box at the end of the compressor. Inside you will see three contacts coming out of the motor, to which the start relay is connected. It is these conclusions that we have to call.
Visual inspection and dismantling of the starting relay
Before taking up the multimeter, carefully inspect the condition of the wires and the relay itself. Often the cause of failure is not the motor itself, but a burnt-out starting device or oxidized contacts. If you notice black traces of soot or smell burning plastic, this is a clear sign of electrical breakdown.
The start relay is usually simply slipped onto the three pins of the compressor and secured with a bracket or spring clip. Carefully remove it, remembering or photographing the position of the contacts, so as not to confuse the top and bottom during assembly.
After removing the relay, you will be left with three protruding contact legs of the compressor. They can be arranged in a triangle or in a row. On the motor body there is often a diagram indicating the contacts: C (Common) - common, S (Start) - starting winding, R (Run) - working winding.
If the marking is erased or missing, do not panic. The location of the contacts is standard for most models, such as Atlant, Indesit or Beko. However, for accuracy, it is better to check the technical documentation of a specific model or find a diagram on the Internet using the engine number.
Clean the contacts from possible oxide or carbon deposits with a soft, dry cloth. Dirt on the contacts can significantly distort the readings of the multimeter, creating a false impression of high resistance or an open circuit.
Setting up the multimeter and searching for a common contact
To take measurements, switch the multimeter to resistance measurement mode. Typically this is a sector indicated by the symbol Ω (Ohm), and the measurement limit is 200 Ohm or 2 kOhm. If your device has a “dialer” function with an audible signal, it will also be useful for quickly checking integrity.
The first task is to find a common contact. To do this, you need to alternately touch the pairs of contacts with the probes and record the readings. For a working engine, the sum of the resistances between two pairs of contacts should be equal to the resistance of the third pair.
Take three measurements:
- 📏 Measurement between the first and second contacts.
- 📏 Measurement between the second and third contacts.
- 📏 Measurement between the first and third contact.
The contact that participates in two measurements with the lowest resistance values will be common. For example, if between contacts A-B the resistance is 20 Ohms, between B-C - 15 Ohms, and between A-C - 35 Ohms, then contact B is common, since 20 + 15 = 35.
It is important to understand that resistance values can vary in depending on the engine power and its manufacturer. For household refrigerators, the normal range is from 10 to 50 Ohms for working windings.
Diagnostics of windings: starting and working
After you have identified the common contact, you need to determine which of the remaining two pairs is starting and which is working. This is critical to understanding the condition of the engine. The starting winding always has higher resistanceas it is made of a thinner wire and is intended only for short-term starting.
The working winding, on the contrary, should have less resistance, since the main current flows through it during operation of the compressor. The difference in readings can be significant: for example, 15 Ohms for the working winding and 30 Ohms for the starting winding.
If you received values that fit into the logic “sums equal to a whole” and differ in value, this is a good sign. However, if the resistances of both windings are the same or differ slightly, this may indicate an interturn short circuit.
⚠️ Attention: An interturn short circuit is difficult to diagnose only with a multimeter. If the engine hums but does not start, and the resistance of the windings is normal, the problem may lie in a short circuit of the turns, which requires replacing the compressor.
The table below shows approximate resistance values for different types of compressors so that you can navigate the data obtained:
| Type compressor | Working winding resistance (Ohm) | Starting winding resistance (Ohm) | Total resistance (Ohm) |
|---|---|---|---|
| Low-power (up to 100 W) | 25 - 35 | 40 - 55 | 65 - 90 |
| Medium power (150-200 W) | 12 - 20 | 25 - 35 | 37 - 55 |
| High power (250+ W) | 8 - 15 | 15 - 25 | 23 - 40 |
| Inverter (for reference) | Unstable | Unstable | Requires special. test |
Please note that for inverter models, conventional resistance measurements are often uninformative, since their motors have a different design and are controlled by complex electronics. In such cases, it is better to contact a specialist.
Checking for breakdown of ground (short circuit to the housing)
The most dangerous defect that a multimeter can detect is a breakdown of the insulation of the windings on the motor housing. If the phase shorts to the metal case, when turned on, the circuit breaker will be knocked out or an electric shock will occur when touching the refrigerator.
To check, switch the multimeter to the resistance measurement mode at the maximum limit (usually 2 MOhm or 20 MOhm). Press one probe tightly to any of the three contacts on the compressor, and the second to the metal part of the motor housing, which has been cleaned of paint and rust.
The device should show infinity (number 1 on the left on the display or the inscription OL). If you see any resistance values, even very large ones (for example, 500 kOhm or 2 MOhm), this indicates an insulation failure.
Why can’t you ignore a small leakage current?
Even if the breakdown resistance is high and the machine does not knock out immediately, such a compressor is dangerous. Over time, the insulation will deteriorate further, leading to a complete short circuit and possible fire of the wiring.
Repeat the procedure for all three contacts. In no case should there be contact with the housing. If a breakdown is detected, operation of the refrigerator is prohibited, as this threatens people's lives.
Sometimes a false breakdown can occur due to moisture or oil on the terminal block. Thoroughly wipe and dry the contact area with a hairdryer (on a cold setting) and repeat the measurements.
Interpretation of results and typical faults
The data obtained must be interpreted correctly in order to make the right repair decision. There are several scenarios that you may encounter during the diagnostic process.
If the multimeter shows infinity (open) between any two winding contacts, this means that the wire inside the motor has burned out. It is impossible to restore such a motor; a complete replacement of the compressor is required.
If the device shows zero or values close to zero, this indicates a short circuit inside the windings. In this case, the motor must also be replaced, since rewinding in domestic conditions is impractical and not economically justified.
☑️ Diagnostic checklist
In a situation where all measurements are normal, but the refrigerator does not work, the problem may not be in the electrical part of the motor, but in the mechanical part. The piston could have jammed due to exhaustion or lack of lubrication.
There is a method of “wedging” by applying increased voltage, but it is extremely dangerous and requires special equipment. Without proper experience, it is better not to experiment, since you can finally finish off working electrics.
Frequent diagnostic errors and precautions
Beginners often make mistakes that lead to incorrect conclusions. One of the most common is checking without removing the start relay. If the relay is left in place, you are measuring the resistance of the relay coil itself, and not the motor windings.
Another mistake is using a faulty or discharged multimeter. Always test the device with a known resistance or by shorting the probes to each other before starting work.
⚠️ Attention: Do not try to start the compressor directly from the mains for testing unless you have the skills of an electrician. This may result in an explosion of the start capacitor or personal injury due to high system pressure.
It is also important to consider the temperature of the motor. If you just turned off the refrigerator, the windings may be hot, which slightly changes their resistance. Allow the unit to cool to room temperature before taking measurements.
Remember that even if the electrics are in order, this does not guarantee 100% serviceability of the compressor. Mechanical defects, such as valve wear or loss of compression, cannot be determined with a multimeter.
If after all the tests you doubt the results, it is better to play it safe and call a professional technician with a manifold gauge to check the pressure in the system.
Final repair recommendations
Diagnosing a compressor with a multimeter is a powerful a tool that allows you to weed out many false breakdowns. If your measurements show an open circuit, a short circuit or a breakdown in the housing, then replacing the motor is inevitable.
When replacing a compressor, it is important to select an analogue with the same or greater performance, as well as the appropriate refrigerant. Modern environmentally friendly freons require the use of synthetic oils that cannot be mixed with mineral ones.
If you decide to replace the compressor yourself, remember that this will require a vacuum pump and a refrigerant charging station. You cannot simply “solder” a new motor without vacuuming the system - residual moisture and air will damage the new compressor in a matter of days.
In cases where the electrical parameters are normal, but the refrigerator does not freeze, look for the cause in other components: thermostat, relay, defrost sensors or freon leak. An integrated approach to diagnostics will save you time and money.
Is it possible to check the compressor without removing the relay?
No, this is impossible. The start relay closes the winding contacts, and you will be measuring the resistance of the internal components of the relay itself, not the motor. For accurate diagnostics, the relay must be removed.
What resistance is considered normal for a household refrigerator?
The normal range for the working coil is considered to be 10-30 Ohms, for the starting coil - 20-50 Ohms. The exact values depend on the motor power. The main rule: the sum of two smaller resistances should be equal to the third (common).
What to do if the multimeter shows 0 Ohm?
A reading of 0 Ohm (or close to it, for example, 0.5 Ohm) indicates a short circuit in the windings. Such a compressor is faulty and requires replacement; it is dangerous to operate.
Why does the compressor hum but does not start?
This may be a sign of a jammed mechanical part, an interturn short circuit, or a faulty start relay. If the electrical resistance is normal, most likely the problem is mechanical or in the starting device.
Is a breakdown on the housing dangerous if the machine does not knock out?
Yes, it is dangerous. Even a weak leakage current can accumulate on the metal body of the refrigerator. If touched by a person standing on a wet floor, this can lead to a serious electric shock.