Diagnostics of the refrigerator compressor with a multimeter: a complete guide with video tips

Sudden A refrigerator breakdown often comes as an unpleasant surprise, causing you to panic due to the risk of food spoilage. One of the first symptoms of unit failure is the absence of the characteristic hum of the motor or, conversely, its humming without starting, when compressor cannot start. In most cases, the reason lies in the starting relay or thermostat, but one should not exclude a more serious problem - a burnt-out motor winding.

Before calling a technician or buying a new unit, it makes sense to carry out initial diagnostics yourself, using a regular one. multimeter. This device allows you to accurately determine the integrity of electrical circuits and the presence of a short circuit. In this article, we will look in detail at how to check the compressor on a refrigerator with a multimeter, based on proven methods and technical standards.

To carry out the work, you do not need complex industrial equipment, just a basic set of tools and compliance with electrical safety rules. We will look at the stages of preparation, the process of taking resistance readings and the interpretation of the data obtained so that you can accurately say whether the motor can be restored or requires replacement.

Preparation for diagnostics and safety measures

Any work related to the electrical components of household appliances requires strict adherence to safety precautions. The first and most important step is to completely disconnect the refrigerator from the AC power. It is not enough to simply turn off the button; you must unplug the cord from the outlet to eliminate the risk of electric shock during measurements.

After disconnecting the power, you need to gain access to the lower rear part of the unit, where the motor-compressor is located. Depending on the refrigerator model, for example Indesit or Atlant, you may need to remove the protective cover secured with screws or plastic latches. Be careful, as the edges of the metal casings may be sharp.

⚠️ Attention: It is strictly forbidden to measure resistance on the windings if the compressor is energized. This is guaranteed to lead to failure of the multimeter and can cause serious electrical injury.

To carry out high-quality diagnostics, you will need the following tools:

• 🔧 Screwdriver (Phillips or flat) for removing covers.
• 🔌 Multimeter (digital or analog) with a continuity function.
• 🧤 Dielectric gloves for additional protection.
• 🧹 Dry rags for cleaning the contacts from dust and oxides.

Before starting measurements, make sure that the contacts on the compressor terminal block are dry and clean. Oxides or moisture can distort the instrument readings, creating a false impression that the windings are faulty. If you see traces of corrosion, carefully clean the contacts.

Removing the starting relay and accessing the contacts

To ring the windings, you need to gain direct access to three contacts coming out of the compressor housing. They are covered by a plastic block called a start relay. This element is responsible for supplying voltage to the starting winding when the engine starts.

The dismantling process usually does not cause difficulties even for beginners. The relay fits directly onto the compressor terminals and is secured with a clamp or screw. Carefully disconnect the wires going to the relay and remove the unit itself. Below it you will see three pins arranged in a triangle.

These pins correspond to different motor windings. They are usually marked with letters or colors, but the markings may fade over time. In the classic circuit, the arrangement is as follows: the two upper contacts are responsible for the starting and working windings, and the lower (or side, depending on the model LG or Beko) is the common terminal.

📊 What problem did you encounter when disassembling the relay?

Rusty bolts

Broken plastic

It is not clear how to remove

No problems

It is important not to damage the fragile ceramic insulators around the terminals when removing the relay. If the relay has mechanical damage or traces of burning, this may indicate that the problem lies with it, and not with the motor itself. However, for accurate diagnostics, you need to check the entire circuit.

Search for a common point and winding diagram

Before starting measurements, you need to understand which of the three contacts is common. This is a critical step because incorrectly defining the findings will lead to misinterpretation of the results. In most modern compressors, the contact layout is standardized, but it is better to double-check visually.

The common contact is often located separately from a pair of others or is marked C (Common). The remaining two contacts are the working winding (Running) and the starting winding (Starting). The working winding always has a larger wire cross-section, so its resistance will be lower.

To determine the contacts, you can use a visual inspection of the internal structure through the holes in the case, if they are visible, or rely on standard logic: the resistance between the common wire and the working wire is always less than between the common and starting. The sum of these two resistances should be equal to the resistance between the starting and operating contacts.

⚠️ Attention: On some compressor models, especially old Soviet or specific Chinese brands, the location of the contacts may differ from the standard. Always check the technical documentation for your specific model, if available.

If the markings are erased, use the elimination method. Call all three pairs of contacts. The pair that gives the highest resistance does not use the common wire directly in standard operation, but shows the sum of the resistances of the two windings. The contact that participates in both smaller measurements is the desired common point.

Checking the windings for open circuits and short circuits

Now we move on to the main stage - measuring resistance. Switch the multimeter to resistance (ohms) measurement mode, selecting a limit of 200 ohms or 2 kohms. First, let's check the circuits for open circuits, which is a common cause of equipment failure.

Attach the probes to a pair of contacts. If the multimeter display shows one on the left (infinity) or the meter makes an intermittent sound, this indicates an open circuit. The whole winding must show a specific numerical value, usually in the range from 10 to 50 Ohms for the working winding and slightly higher for the starting winding.

☑️ Multimeter testing algorithm

Set mode 200 OhmShort the probes for testing zeroMeasure R between the general and the workingMeasure R between the general and the startingCompare the sum with R between the working and the starting

Done: 0 / 5

Next we check the absence of a short closures. To do this, apply one probe to any contact of the compressor, and the second to the copper tube on the body (after cleaning a small spot from paint to metal). The device should show infinity. If you see any resistance values, it means that an insulation breakdown has occurred on the housing.

The table below shows approximate resistance values for working compressors of various capacities:

Winding type	Normal resistance (Ohm)	Symptom malfunction
Running	10 – 35 Ohm	0 Ohm (Short circuit) or ∞ (Open)
Starting	20 – 60 Ohm	0 Ohm (Short circuit) or ∞ (Open)
Case (Breakdown)	∞ (Infinity)	Any numerical value

If the values differ greatly from the table ones, for example, the resistance of the working winding is significantly higher than the starting winding, this is a sure sign of an interturn short circuit or wire degradation. In this case, the compressor will not work or will constantly knock out the circuit breaker.

Diagnostics of thermal protection and start relay

Often the problem lies not in the motor itself, but in the attachment. The starting relay and thermal protection (thermal relay) are elements that fail even more often than the motor windings. Thermal protection is a bimetallic plate that opens the circuit when overheated.

To check the thermal protection, you need to ring its contacts in a cold state. The multimeter should read zero or very close to zero, indicating a closed circuit. If the device shows a break, it means that the protection has burned out or does not return to its original state.

The starting relay is checked visually and for the resistance of the coil (if it is electromagnetic). There should be no melted plastic inside, and the contacts should not be burnt. For reed switch relays, it is important to check whether the contact closes when a magnet is approached or the device is turned over, depending on the design.

Why does it hum, but does not start?

If the compressor hums, but does not start, and the machine knocks out, most likely the piston group is jammed or a strong inter-turn short circuit has occurred. Attempts to “unlock” by applying 220V voltage are often dangerous and require special equipment.

Replacing these components is inexpensive and often revives the refrigerator without the need to replace an expensive compressor. Make sure that the new relay is suitable in terms of power and type of connection to your model Samsung or Stinol.

Analysis of results and decision making

After receiving all the data, you need to make a final conclusion. If the windings are intact, there is no breakdown to the housing, and the relay and thermal protection are working, but the refrigerator does not work, the problem may be in the wiring, thermostat or electronic control module. In this case, diagnostics with a multimeter only narrowed the search.

If the measurements showed a break in the winding or a breakdown in the housing, the compressor is considered faulty. It is impossible to restore a burnt out winding at home, since it is necessary to rewind the stator at the factory or replace the entire assembly.

If an interturn short circuit is detected (when the resistance is below normal, but there is no break), operation of such a compressor is possible for a short time, but it will heat up very much and consume more electricity. Sooner or later, a complete breakdown will occur.

⚠️ Attention: When replacing a compressor, it is necessary to take into account the refrigerant for which it is designed (R134a, R600a) and the cooling capacity. Installing an unsuitable motor will lead to inefficient operation of the refrigerator.

Do not forget that the final start-up of a new or proven compressor requires evacuation of the system and charging with freon. These operations can only be performed by a specialist using a pressure gauge station and a vacuum pump.

Is it possible to check a compressor without a multimeter?

Theoretically, you can apply voltage directly, bypassing the relay, but this is extremely dangerous and does not provide information about the state of the insulation. Without a multimeter, you will not know whether there is a breakdown on the case, which can lead to an electric shock.

What resistance is considered normal for different brands?

For most household compressors (Indesit, Atlant, Beko), the resistance of the working winding is 15-25 Ohms, and the starting winding is 30-45 Ohms. The values ​​may vary depending on the power of the motor.

Why does the multimeter show zero on the winding?

A reading close to zero indicates a short circuit in the turns. This is a serious malfunction in which the compressor will burn out instantly when connected to the network.

Is it necessary to unsolder the compressor to check?

No, to check the electrical part (windings) you do not need to unsolder the tubes. This is only required when replacing the compressor or checking the pressure in the system.