Has the refrigerator stopped cooling or does it turn on for a few seconds and immediately turn off? Often the culprit of such a malfunction is compressor, which is the “heart” of the entire system. Before calling a technician or buying a new unit, it makes sense to conduct an initial diagnosis of the electrical part of the motor. This will allow you to understand whether the engine is alive or the problem lies in the start relay or thermostat.
To check, you will need a minimum set of tools, the main one of which is multimeter. This device allows you to measure the resistance of the windings and check the integrity of the electrical circuit. If you have never encountered electrical measurements before, carefully follow the instructions so as not to damage the equipment and protect yourself.
In this article we will analyze in detail the algorithm of actions, consider the standard resistance indicators for various types of motors and learn how to distinguish a breakdown to the frame from an open circuit. Competent diagnostics will save you time and money, since replacing a compressor is an expensive procedure that requires qualifications.
Preparation for diagnostics and safety measures
Before starting any work with electrical equipment, you must completely turn off the power to the refrigerator. Unplug the power cord from the outlet. This is a critical step, as operating the multimeter on live circuits without proper training may result in electric shock or damage to the meter.
Move the unit away from the wall to allow access to the rear. You need to find the start protection relay, which is usually mounted on the side of the compressor and covered with a plastic casing. Carefully remove the casing by unscrewing the mounting screws or releasing the plastic latches.
⚠️ Attention: If traces of oil, rust, or melted plastic are visible on the compressor, this may indicate overheating or mechanical damage. In such cases, a visual inspection often provides more information than testing with a multimeter.
For work, prepare multimeter in resistance measurement mode (Ohm). Make sure the probes are working properly and the device battery is charged. You may also need a screwdriver to remove the terminal box cover and pliers to carefully remove the terminals from the motor contacts.
☑️ Preparation for testing
Removing the starting relay and access to the contacts
To get to the winding terminals, you need to remove the starting relay and thermal protector. They are put directly on the contact group of the compressor. The relay is usually fixed with a bracket or simply sits tightly on three pins. Gently loosen it from side to side and remove.
Under the relay you will see three contacts arranged in a triangle. These are the terminals of the motor stator windings. It is important not to confuse their purpose, although this is not always critical for the initial check of circuit integrity. The standard marking of contacts is as follows:
- 🔌 S (Start) — starting winding, has the highest resistance.
- 🏃 R (Run) — working winding, has average resistance.
- ⚡ C (Common) — common wire, the connection point of the windings.
Sometimes color markings or numbers are used instead of letters, so it is best check the technical documentation for a specific model refrigerator. If the relay is removed, inspect it for blackening, cracks, or a burning smell. Often the problem lies precisely in the sticking of the relay contacts, and the motor itself is working properly.
Typical errors when removing a relay
If you remove the relay carelessly, you can damage the ceramic contact insulators or break the plastic clips. Also, do not pull the wires if they are connected to the relay - hold only the body of the part.
Setting up a multimeter and checking the probes
Before touching the motor contacts, make sure that your measuring device is ready for use. Switch the multimeter wheel to the resistance measurement sector, indicated by the Ω (Ohm) symbol. Select the measurement limit of 200 Ohms or 2 kOhms, since the winding resistance is usually in the range from 10 to 100 Ohms.
To check the serviceability of the multimeter itself, short the probes together. Zeros or a value close to zero (wire resistance) should appear on the screen. If the device shows a unit in the most significant digit or chaotic numbers, replace the battery or check the contact of the probes.
It is important to correctly understand the device readings. A unit on the left side of the display (for example, “1” without other numbers) means infinite resistance, that is open circuit. If the device shows values close to zero when measuring the windings, this may indicate a short circuit.
Measuring the resistance of the motor windings
Now we move on to the main part of the diagnosis. We need to “ring” all three contacts in pairs. Touch the probes to contacts S and C, then R and C, and finally S and R. Write down the values obtained so as not to get confused.
In a working engine, the sum of the resistances between the starting and running windings should be equal to the resistance between the corresponding pairs of contacts through the common wire. That is, the resistance between S and R should be approximately equal to the sum of the resistances S-C and R-C. However, in practice, they often look at absolute values.
Resistance within the following limits is considered normal:
- 📉 Between the common wire and the working winding (C-R): 10–30 Ohms.
- 📈 Between the common wire and the starting winding (C-S): 20–60 Ohms.
- 🔄 Between the starting and running windings (S-R): 30–90 Ohms.
If you see that the resistance of one of the windings is significantly different from the norm (for example, 2 Ohms or 500 Ohms), this is a sign of a malfunction. Low resistance indicates an interturn short circuit, and high or infinite resistance indicates a wire break inside the stator.
Checking for breakdown of ground (case)
One of the most dangerous malfunctions is breakdown of winding insulation on the compressor housing. In this case, the engine can work, but touching the metal body of the refrigerator becomes deadly. To check, switch the multimeter to resistance measurement mode at the maximum limit (2 MOhm or 20 MOhm).
Press one probe to any of the three motor contacts, and the second to a place on the metal body of the compressor that has been cleared of paint. If the device shows “1” (infinity), then the insulation is intact. The appearance of any digital values indicates a current leakage to the housing.
⚠️ Attention: Operating a refrigerator with a breakdown to the housing is strictly prohibited. Even if it cools temporarily, the risk of electric shock when touching the body or food in metal containers is extremely high. The compressor needs to be replaced.
Sometimes a breakdown appears only when the engine heats up. In a cold state, the multimeter may show normal values, but when operating under load, the insulation “floats”. Therefore, if in doubt, it is better to use a specialized device - Meggerthat tests insulation under high voltage, but this is a task for service centers.
Table of standard values and faults
For convenience, we systematize the data obtained. Below is a table to help you interpret multimeter readings based on the type of fault. Please note that the exact numbers may vary depending on the power and engine model.
| Measurement type | Normal value | Break sign | Short circuit sign |
|---|---|---|---|
| Winding C-R | 10 – 30 Ohm | ∞ (Unit) | < 5 Ohm |
| Winding C-S | 20 – 60 Ohm | ∞ (Unit) | < 10 Ohm |
| Breakdown on the body | ∞ (Unit) | - | Any number |
If your measurements coincide with the “Normal value” column, but the refrigerator does not start, the problem is most likely not in the windings. In this case, check the start relay, thermostat or defrost system. The electrical part of the motor may be in good working order, but mechanically the pistons may be jammed.
Diagnostics of interturn short circuit
The most difficult case to diagnose is an interturn short circuit. In this mode, the winding resistance may be close to normal, but the motor will consume enormous current, overheat and trip the circuit breaker. It is difficult to identify this with a multimeter, but you can try.
Compare the resistance of the starting and operating windings. Typically, the starting resistance is 1.5–2 times greater than the operating resistance. If the difference is insignificant or the resistances are equal, this is a reason for suspicion. Also pay attention to the color of the oil in the crankcase (if there is access) - when shorted, it often darkens and acquires a burning smell.
Another indirect sign is the behavior of the dial ammeter (if it is possible to connect). When turned on, the current should jump sharply and drop to the operating value. If the current remains high and the compressor heats up quickly, there is an interturn short circuit.
⚠️ Attention: Technical characteristics of compressors from different manufacturers (Danfoss, Embraco, Secop) may differ. The indicated resistance ranges are average values. For accurate diagnostics, check the datasheet of a specific engine.
What to do if the compressor is faulty
If the diagnostics showed an open circuit, a short circuit or a breakdown in the housing, the compressor must be replaced. Repairing windings at home is impossible and economically infeasible. The new engine must have the same cooling capacity and type of refrigerant.
Replacing a compressor requires special equipment: a burner, a vacuum pump and a filling station. It is difficult to perform this operation on your own without experience and tools - there is a risk of damaging the system or improperly soldering the tubes, which will lead to freon leakage.
If the electrical parameters are normal, but the motor does not start, try replacing the start relay. This is an inexpensive part that often fails. If this does not help, a mechanical wedge is likely, and then you cannot do without service intervention.
Is it possible to start the compressor without a relay?
There is a starting method through a capacitor or a button, but this is a temporary measure for diagnostics. Long-term operation without a standard relay will lead to burnout of the windings.
Frequently asked questions (FAQ)
Is it possible to check the compressor without a multimeter?
It is impossible to accurately determine the condition of the windings without a device. You can only indirectly judge the performance: if the engine hums, but does not start, and the relay is working properly, it may be jammed. If there is silence, the thermal protection may break or burn out.
What resistance is considered normal for Atlant or Indesit refrigerators?
For most household refrigerators of these brands, the resistance of the operating winding is about 15–25 Ohms, and the starting winding is 30–45 Ohms. The main rule: the starting winding always has greater resistance than the working winding.
Why does the multimeter show one when testing?
A unit in the most significant digit means an infinitely large resistance, that is, an open circuit. This indicates that the wire inside the winding has burned out and no electric current is passing through it. Such a compressor is faulty.
Is it dangerous to touch the contacts while the refrigerator is on?
Absolutely yes. There is a voltage of 220 Volts at the contacts. All manipulations with the multimeter and removal of the relay are carried out only with the power supply completely disconnected from the mains.