A sudden stop of the refrigerator or its inability to maintain the set temperature often indicates a malfunction of the main unit - the compressor. It is this unit, which in everyday life is often called a motor, that circulates the refrigerant through the system. Before calling a technician or buying new equipment, it makes sense to carry out initial diagnostics yourself, using available tools.
The main device for checking the electrical part of the engine is a multimeter. This compact tester allows you to measure the resistance of the windings, identify an open circuit or a short circuit to the frame. Correct interpretation of the received readings will help to understand whether compressor it is subject to repair or whether it needs to be replaced.
However, it is worth remembering that the electrical serviceability of the windings does not always guarantee the mechanical performance of the unit. The motor may have normal resistance, but jam due to wear on the piston group or loss of compression. However, checking with a multimeter is the first and mandatory stage of diagnosis, eliminating the most common electrical faults.
Preparation for diagnostics and safety precautions
Any work related to electricity and internal components of household appliances requires strict adherence to safety precautions. A refrigerator is a high-voltage appliance, and careless handling of the wiring may result in electric shock. The first step should always be to completely disconnect the device from the electrical network.
To carry out high-quality diagnostics, you will need a digital multimeter capable of measuring resistance in the range from 0 to 2000 Ohms. Also prepare a set of screwdrivers to remove the rear panel and gain access to the compressor compartment. Gloves will be a good idea to protect your hands from sharp metal edges.
⚠️ Attention: It is strictly forbidden to measure resistance or continuity tests while the power cord is connected to the outlet. This is guaranteed to lead to failure of the multimeter and can be life-threatening.
Before starting the test, you must gain access to the motor contacts. To do this, remove the back cover of the refrigerator, which is usually secured with screws or plastic latches. In some models, it is also necessary to remove the protective casing of the compressor itself in order to get to the contact group.
Compressor design and connection diagram
To properly check electric motor, you need to understand its internal structure. In household refrigerators, single-phase asynchronous motors with a starting winding are most often used. Inside the case there are two main windings: working and starting, as well as a thermal protection relay.
The contact group usually has three terminals arranged in a triangle. On different models of refrigerators, be it Indesit, Bosch or Atlant, the markings may differ, but the principle of contact arrangement is the same. It is important not to confuse the conclusions in order to correctly interpret the measurement results.
Deciphering the contact markings
Usually the contacts are designated in Latin letters: C (Common) - common wire, R (Run) - working winding, S (Start) - starting winding. In some cases, numerical or color markings are used, depending on the motor manufacturer.
There must be perfect insulation between the windings and the metal body of the motor. Violation of this layer leads to a breakdown on the housing, which triggers the circuit breakers in the apartment and makes operation of the device impossible. It is the integrity of the insulation that we will check first.
Step-by-step instructions: checking the windings for resistance
The diagnostic process begins with a visual inspection of the contacts for oxidation or carbon deposits. If the terminals look normal, you can start measuring. Switch the multimeter to resistance measurement mode (Ohm) to the limit of 2000 Ohm or 2 kOhm.
First of all, you need to find the common terminal. To do this, measure the resistance between all three contacts one by one. The pair of contacts that gives the greatest resistance is the ends of the starting and operating windings. The third, remaining contact is general conclusion.
☑️ Algorithm for checking the windings
After identifying the common contact, measure the resistance between it and the other two terminals. The resistance of the working winding is usually 10-20 Ohms, and the starting winding is 30-50 Ohms. The sum of these two values should be equal to the resistance between the extreme contacts (starting and working).
If the device shows infinity (one on the left of the screen), this indicates an open circuit. In such a situation, it is almost impossible to restore the motor; it needs to be replaced. Values that are very different from the norm indicate an interturn short circuit.
Diagnostics of breakdown on the motor housing
One of the most dangerous malfunctions is an insulation breakdown when voltage hits the metal body of the refrigerator. This not only disables the equipment, but also creates a direct threat to the lives of users. You can check for breakdown using the continuity function or resistance measurement.
To carry out the test, select the resistance measurement mode on the multimeter at the maximum limit (for example, 200 kOhm or 2 MOhm) or the audio test mode. Press one probe to any of the three contacts on the compressor, and the second to a clean, unpainted part of the metal motor housing or copper tube.
In good condition, the device should show infinite resistance or no sound signal. Any readings, even minimal ones, indicate a violation of insulation. In this case, operation of the refrigerator is prohibited.
| Measurement type | Normal reading | Malfunction symptom | Action |
|---|---|---|---|
| Working winding | 10–20 Ohm | 0 Ohm or ∞ | Replacing the compressor |
| Starting winding | 30–50 Ohm | 0 Ohm ∞ | Replacement of the compressor |
| Insulation (housing) | ∞ (infinity) | Any number | Urgent replacement |
| Thermal relay | 0 Ohm (closed) | ∞ (open) | Replacing the relay |
Checking the starting and thermal relay
Often the reason that the motor does not start is not the compressor itself, but a malfunction of the starting or thermal relay. These small devices are responsible for starting the engine and protecting it from overheating. Before sinning on an expensive motor, be sure to check these elements.
The thermal relay in a cold state should ring short (resistance is close to zero). If the circuit is open, the relay must be replaced. The starting relay is checked in the same way, but it is important to take into account its orientation, since there may be a ball or spring inside.
Visually inspect the relay for cracks, melting or a burning smell. If soot or traces of carbon deposits on the contacts are visible inside the device, its further operation is unacceptable. The cost of new relays is low, so replacing them is often more expedient than diagnostics.
Sometimes a situation occurs when the windings are intact, the relays are working, but the engine hums and does not start. This may indicate that the piston group is jammed. In such cases, sometimes a short-term supply of voltage through a capacitor helps, but this method requires high qualifications and is dangerous.
Analysis of results and common errors
After all measurements have been carried out, it is necessary to analyze the data obtained. If the winding resistance is normal, but the refrigerator does not operate, the problem may lie in the refrigerant circulation system or the electronic control module. A multimeter will not help diagnose capillary tube blockage.
One of the common mistakes of beginners is measuring resistance on dirty or oxidized contacts. Oxides create additional resistance, distorting the readings. Always clean the contacts with fine sandpaper before diagnostics.
⚠️ Attention: Do not try to start the compressor directly from the network without a start relay to check if you are not sure of your actions. This can lead to burnout of the windings or injury.
It is also worth considering that for some motor models the winding resistance may be very low, less than 1 Ohm. Cheap multimeters may show incorrect values in this case. To accurately diagnose such motors, more professional instruments are required.
If diagnostics show that the motor is faulty, do not rush to throw away the old unit. It contains copper, which can be taken to collection points for non-ferrous metals. This will partially offset the cost of purchasing a new compressor.
Frequently asked questions (FAQ)
Is it possible to restore a broken compressor winding?
Theoretically, rewinding is possible, but in practice it is not economically feasible. The cost of work and materials often exceeds the price of a new compressor, and there is practically no guarantee for such repairs.
Why does the multimeter show different resistance values when repeated measurements?
The resistance of the windings depends on temperature. As the engine heats up, the resistance increases. For accurate measurements, allow the compressor to cool completely for several hours.
A humming motor without starting is always a break?
Not necessary. A humming sound may mean that the starting relay is faulty and does not send an impulse to the starting winding, or the mechanical part of the engine is jammed.
Which multimeter is best to choose for repairing refrigerators?
Any digital tester with a continuity function and resistance measurement up to 2000 Ohms is suitable for household use. Professionals require devices with higher accuracy and protection from high voltage.