A sudden stop of the refrigerator often confuses the owner, especially when there are perishable foods inside. Before calling a technician or buying new equipment, it makes sense to conduct an initial diagnosis of the core of the unit - compressor. It is this unit that is responsible for circulating the refrigerant and creating the necessary pressure in the system. Incorrect diagnostics can lead to the purchase of unnecessary spare parts or, conversely, to ignoring a real breakdown, which can lead to complete failure of the unit.
The most affordable and reliable tool for checking the electrical part of the engine is multimeter. This device allows you to measure the resistance of the windings, detect a short circuit or open circuit, and also check for a breakdown in the housing. Unlike a visual inspection, which often yields nothing, working with a tester provides accurate digital data about the condition of internal components. However, it is worth understanding that the multimeter will not show mechanical jamming or loss of compression; it only diagnoses electrical integrity.
It is important to understand that any work with electrical appliances requires compliance with safety precautions. Refrigerator is a complex device that operates under high voltage. Before starting any manipulations, it is necessary to completely de-energize the unit by removing the plug from the socket. Failure to do so may result in electric shock or damage to the control electronics. In this article, we will analyze in detail the algorithm of actions that will allow you to independently determine the serviceability of the motor.
⚠️ Attention: If you find melted plastic, traces of burning, or smell burnt insulation in the compressor area, further independent diagnostics can be dangerous. In such cases, there is a high probability of an internal fire in the windings, and the best solution would be to call a specialist.
Preparation of the workplace and tools
Quality diagnostics is impossible without proper preparation. You will need not only the multimeter itself, but also a set of tools to access the technical compartment. Typically the compressor is located at the bottom rear of the refrigerator and is covered with a metal or plastic casing. To remove it, you will need screwdrivers (Phillips and flat head), and possibly also pliers for removing terminals. Make sure you have good lighting, as the back wall of the refrigerator is often in a dark area.
The main tool will be multimeter. It can be analog (with an arrow) or digital. Digital models are preferable due to higher accuracy of readings and ease of reading data. Before starting work, check the battery charge of the device, as a dead battery may give false resistance readings. Switch the device to the resistance measurement mode (Ohm), selecting a limit of 200 Ohms or a continuity mode.
Also prepare a clean rag to wipe the contacts from dust and possible oxides. Dirt on the terminals can significantly distort the measurement results. If the terminals are oxidized, they should be carefully cleaned with fine sandpaper or a file before connecting the probes. This will ensure reliable contact and reliability of measurements.
- 🛠️ Set of screwdrivers: for removing the protective casing and terminal box.
- 🔋 Multimeter: digital or analog, with working probes.
- 🧼 Cleaning agents: rags, alcohol or contact spray for cleaning terminals.
- 🧤 Protective gloves: to protect hands from sharp metal edges and possible residual oil.
☑️ Ready for diagnostics
Access to the compressor and removal of the terminal box
First you need to gain physical access to the electrical terminals of the compressor. Move the refrigerator away from the wall to allow easy access to the rear panel. Locate the casing covering the motor-compressor. It is usually secured with latches or screws. Carefully remove it, trying not to damage the plastic elements, which could become fragile over time.
On the compressor body you will see a small plastic box - a start-up relay. It is inside it that there are contacts going to the motor windings. The box is fixed to the three terminals of the compressor and, possibly, an additional clamp. Carefully remove the relay cover to gain access to the contact group. At this stage, it is important not to mix up the wires during subsequent assembly, so it is recommended to take a photo or mark them with a marker.
Remove the terminal block from the compressor terminals. This must be done carefully, loosening from side to side, but without using excessive force, so as not to break the plastic clips. After removing the block, you will see three pins on the motor housing, arranged in a triangle. These are the winding inputs. Before measurements, wipe them with a dry cloth, removing any possible contamination.
Nuances of relay location
In some models of refrigerators, especially built-in or older series, access to the compressor may be difficult due to the design of the cabinet. In such cases, it may be necessary to partially disassemble the rear panel or remove the bottom of the refrigerator. Always check the instructions for your model to clarify the access points.
Determination of winding and contact circuits
Before starting measurements, you need to understand which contacts are responsible for what. There is usually a marking on the block or in the technical documentation, but if it is erased, you will have to use the method of elimination. A standard compressor has three terminals: two for the working and starting windings and one common. The resistance between these terminals will be our main indicator of the condition.
Visually inspect the terminals. They can be signed with the letters R (Run - working winding), S (Start - starting winding) and C (Common - common). If there are no markings, you will have to calculate them empirically. The working winding always has a larger wire cross-section, which means less resistance, but when paired with the starting winding it gives the highest total resistance. The starting winding is thinner and has greater resistance.
For accurate diagnostics, it is important to know that we are not looking for absolute values, but ratios. Resistance may vary depending on the power of the motor and the manufacturer, but the distribution logic remains unchanged. If you see traces of soot or oxidation on the contacts, this is already a sign of problems with the contact group, which could lead to overheating.
| Pair of contacts | Expected value (Ohm) | Characteristics |
|---|---|---|
| Common - Working | 10 - 25 Ohm | Lowest resistance |
| General - Starting | 20 - 40 Ohm | Average resistance |
| Working - Starting | 30 - 60 Ohm | Sum of the previous two |
| Any - Housing | Infinity (1) | Dielectric insulation |
The process of measuring winding resistance
Now we move on to direct measurements. Set the multimeter to resistance measurement mode (200 ohm limit). Touch the probes to any two terminals of the compressor. Record the reading. Then switch the probes to another pair and record the result again. In total, you will have three measurements between three pins.
Analyze the data obtained. As already mentioned, one of the measurements will show the highest value - this is the resistance between the working and starting windings. The other two measurements will show lower values. The output that participates in both dimensions with smaller values is general. The terminal that gives the least resistance with the common one belongs to the working winding, and the remaining one to the starting winding.
It is considered normal if the resistance values are in the range from 10 to 60 Ohms, depending on the model. The main thing is that they are not equal to zero and do not show infinity (if we are not measuring on the body). If the multimeter shows "1" or "OL" between the winding terminals, this indicates break chains. If it shows “0” or close to zero, there is a short circuit of the turns.
Diagnostics of breakdown to the housing (short to ground)
One of the most dangerous faults is breakdown of winding insulation to the compressor housing. In this case, voltage may appear on the metal body of the refrigerator, which creates a direct threat to human life. It is necessary to check this parameter, even if the winding resistance is normal.
To check, switch the multimeter to the resistance measurement mode at the maximum limit (usually 200 kOhm or 2 MOhm) or to the dialing mode with sound. Press one probe tightly to any of the three terminals of the compressor (after making sure that it is clean), and the second to a cleaned place on the metal body of the motor, where there is no paint, rust or oil.
If the device shows one (infinity) and is silent, then the insulation is intact. If the multimeter makes a squeak or shows any resistance value (even a large one, for example, 50 kOhm), this is a sign of an insulation failure. Operating such a refrigerator is strictly prohibited without replacing the compressor, since the risk of electric shock is extremely high.
⚠️ Attention: When checking for breakdown, make sure that you touch the metal part of the case with the probe, and not plastic elements or an oil film, which can give a false high resistance. Scrape off a small area of paint to ensure contact.
Analysis of results and possible malfunctions
After receiving all the data, it is necessary to draw conclusions. If all three resistances between the terminals are present, their sum converges, and there is no breakdown to the housing, then the electrical part of the compressor is operational. In this case, the problem with the refrigerator may lie in the start relay, thermostat, or freon leak. The motor may be electrically functional, but mechanically jammed.
If a break is detected (infinity between the terminals), this often means the thermal protection inside the compressor has burned out or a wire break at the soldering point. In some cases, the thermal protection can be replaced, but more often this requires replacing the entire unit. A short circuit (zero Ohm) indicates an interturn short circuit, which is a fatal defect.
It is also worth considering the influence of temperature. Resistance copper depends on temperature: the colder the motor, the lower the resistance. Therefore, measurements taken on a cold and hot compressor may differ by 10-15%. This is fine. However, sudden jumps or absence of readings are an alarming signal.
- 🔥 Overheating: If the motor is hot, let it cool before taking measurements for accuracy.
- 📉 Interturn: Often accompanied by humming and knocking out plugs, but the resistance may be normal (checking with current clamps is required).
- 🔌 Relay: If the motor is working but does not start, check the starting relay and capacitor.
Is it possible to start the compressor directly without a relay?
Technically, you can start the motor by applying voltage to the working and starting windings, but doing this without skills and special starting devices is dangerous. Incorrect phase or timing of voltage applied to the starting winding can instantly burn out the motor or cause the capacitor to explode. It is recommended to use only a standard or similar relay.
Why does the multimeter show different values when taking repeated measurements?
This may be due to poor contact of the probes, oxidation of the leads, or residual charge in the windings (although this is rare for low-voltage circuits). Temperature also has an effect: if the motor was running, its resistance will increase as it cools. For accuracy, clean the contacts and wait until the readings stabilize.
What to do if the resistance is normal, but the refrigerator does not freeze?
If the electrical part is intact, the problem may be mechanical: a jammed piston, loss of compression (valve) or a refrigerant leak. In this case, the multimeter is powerless. It is necessary to connect a pressure manifold to check the pressure in the system and listen to the operation of the motor under load.