A sudden stop in the operation of the refrigerator often becomes an unpleasant surprise, especially when food in the chamber begins to spoil. The first sign of a serious breakdown is usually the hum of the motor, which ends abruptly with a click of the relay, or complete silence when turned on. In most cases, the cause of failure is compressornamely a violation of the integrity of its electrical windings. Diagnostics of this part requires care and basic skills in working with measuring instruments, but is quite doable at home.
Before proceeding with disassembly and testing, you must clearly understand the structure of the electric motor. A refrigerator compressor is a unit in which electrical energy is converted into mechanical movement of a piston. Inside the sealed casing is electric motorconsisting of a rotor and a stator with coils wound on it. It is these coils, called windings, that create the magnetic field that turns the rotor. If a wire break or short circuit occurs in them, the engine stops functioning and the cold in the chambers disappears.
There are several typical failure scenarios: a complete open circuit, an interturn short circuit or a breakdown to the housing. Each of these defects has its own symptoms and detection methods. It is critically important before starting any work to completely disconnect the refrigerator from the power supply by unplugging the plug from the socket, since you will be working with conductive elements. Carelessness in this matter can lead to electric shock or damage to measuring equipment.
Preparation for diagnostics and necessary tools
For a high-quality check of the windings, you will need a minimum set of tools that any home craftsman should have. The main device is multimeter (tester), capable of measuring resistance in Ohms. Without this device, diagnostics will be impossible, since it is impossible to visually determine the integrity of the thin copper wire inside the stator. You will also need a screwdriver to remove the compressor protective casing and, possibly, pliers to remove the terminals.
The preparation process includes not only finding tools, but also ensuring safe access to the contact group. The compressor is located at the bottom rear of the refrigerator and is often covered with a metal or plastic box. You will need to remove the back wall or protective cover to gain access to the motor. Then carefully remove the start-up relay, which is placed on three contact pins protruding from the compressor housing.
It is important to inspect the contacts for oxidation or carbon deposits. If the terminals are coated with oxides, the multimeter readings may be distorted, leading to false conclusions about a malfunction. Clean the contacts with fine sandpaper or a file. Make sure you are working in a dry area and your hands are not wet, as humidity will affect the accuracy of resistance measurements.
⚠️ Attention: Never attempt to remove relays or terminals while the refrigerator is plugged in. Even briefly touching live parts is dangerous to life. Also avoid sudden movements so as not to damage the copper tubes coming from the compressor - their repair requires special equipment and evacuation of the system.
☑️ Preparation for checking the compressor
Connection diagram and types of windings
To correctly interpret the instrument readings, you need to understand how the electrical circuit of a single-phase refrigerator motor works. The stator usually contains two main working windings: starting and working. They are wound with copper wire of different diameters and have different numbers of turns, which determines their electrical resistance. The starting winding has a thinner wire and a larger number of turns, so its resistance is always higher.
The contact group of the compressor has three terminals, which are often designated by letters or symbols. In European markings these are S (Start - start), R (Run - work) and C (Common - general). In some models of domestic or Asian production, the markings may differ, but the principle remains the same: one contact is common to both windings, and the other two lead to the starting and working coils, respectively. Understanding this logic allows you to calculate the purpose of the contacts even without a diagram.
Inside the housing, the windings are connected in a certain way. The working winding is connected directly to the network and creates the main rotating magnetic field. The starting winding is turned on only at the moment of start through a capacitor or starting relay, creating an additional phase shift to start the rotor. After gaining speed, the starting circuit opens. If you mix up these windings when connecting, the engine may hum, but not start, or quickly burn out due to overheating.
Features of three-phase compressors
Modern inverter refrigerators and some industrial models can use three-phase compressors. They have three windings connected either in star or delta, and the resistance between any two terminals must be the same. Checking such motors requires more in-depth knowledge and often a special tester to check the insulation.
Step-by-step instructions: how to ring the contacts
The process of measuring resistance requires sequential execution of actions to obtain reliable results. First, set the multimeter to resistance measurement mode (ohmmeter), selecting a limit of 200 ohms or 2 kohms. If the device has a dialing mode with an audible signal, use it for an initial check for a break, but for accurate diagnosis you need digital values.
You need to take measurements between three pairs of contacts. Let's designate the contacts conventionally as 1, 2 and 3. First, attach the probes to contacts 1 and 2, write down the reading. Then measure the resistance between contacts 2 and 3. The third measurement is made between contacts 1 and 3. In total, the resistance between the extreme contacts (for example, start and operation) should be equal to the sum of the resistances of the remaining pairs, if one of the contacts is common.
A typical picture of a working compressor looks like this: between the common contact and the working contact, the resistance is minimal (for example, 15-25 Ohms), between the common and starting - significantly higher (30–50 Ohms), and between starting and operating - the sum of these values. If you see such proportions, it means that the integrity of the windings is most likely preserved. Significant deviations from this logic indicate a defect.
Analysis of results and table of normal values
The data obtained must be compared with reference values for compressors of household refrigerators. While the exact numbers vary depending on motor power and manufacturer, general resistance ranges are fairly universal. Below is a table that helps classify the condition of the windings.
| Measurement type | Normal value (Ohm) | Fault symptom | Probable cause |
|---|---|---|---|
| Operating winding | 10 - 30 Ohm | Infinity (∞) | Wire break |
| Start winding | 20 - 60 Ohm | Close to 0 Ohm | Short circuit |
| Between windings | Sum Rwork + Rstart | Inconsistency with the sum | Burnt insulation |
| Winding - Housing | Infinity (∞) | Any value | Breakdown to housing |
If the resistance is working windings are close to zero, this indicates turn-to-turn short circuit. In this case, the engine may try to start, but will make a loud noise, overheat and knock out the circuit breaker or relay. This malfunction is often accompanied by a burning smell. Unfortunately, it is almost impossible to rewind the stator in an apartment due to the difficulty of access and the need to use special varnish and equipment.
Special attention should be paid to checking for insulation breakdown. To do this, one multimeter probe is applied to any contact, and the second one is applied to a copper tube or an unpainted part of the compressor housing. The device should show infinity. If the arrow deviates or numbers appear, it means that the insulation is broken and current flows to the housing. Operating such a refrigerator is strictly prohibited due to the risk of electric shock.
⚠️ Attention: In some compressor models (for example, Danfoss or Secop) the winding resistance may be very low, about 4–8 ohms. In such cases, the error of a cheap multimeter can be large. Always check the technical documentation of the specific refrigerator model.
Diagnostics of interturn short circuit
The most difficult defect to identify is an interturn short circuit, when the insulation between the turns of the wire is broken, but there is a complete break no. A multimeter in ohmmeter mode may show resistance close to normal, but the engine will not run. This happens because some of the turns fall out of operation, and the magnetic field becomes insufficient to rotate the rotor under load.
An indirect sign of an interturn short circuit can be the behavior of the compressor when trying to start. It may jerk, buzz for a few seconds and then turn off with a thermal relay. This is also indicated by the rapid and strong heating of the motor housing even when running idle (without freon and pressure), although it is not recommended to carry out such experiments without a pressure gauge station.
For more accurate diagnostics, professional services use a device that measures current consumption. With an interturn short circuit, the current in the windings will significantly exceed the rated one indicated on the nameplate. If you do not have an ammeter, you can use the exclusion method: if the relay and capacitor are working properly, but the motor does not start and hums, the probability of an interturn short circuit is extremely high.
Frequent errors during testing and safety measures
When self-diagnosing, technicians often make mistakes that lead to incorrect ones. One of the most common is measuring resistance on dirty or oxidized contacts. The oxide film creates additional resistance, which the device perceives as a winding malfunction. Always clean the contacts to a metallic shine.
Another mistake is ignoring the thermal state of the motor. Copper resistance depends on temperature: the hotter the windings, the higher their resistance. If you just turned off a running refrigerator and immediately started measuring, the readings may be higher than actual ones. Allow the compressor to cool to room temperature before diagnostics.
Do not forget about safety when working with refrigeration equipment. The system circulates refrigerant under pressure. Do not bite or kink copper tubing. If the compressor requires replacement, the old unit must be disposed of correctly, since it may contain oil and freon residues.
Is it possible to start the compressor directly?
Theoretically, by applying voltage to the operating and starting windings (via a capacitor), you can start the motor outside the refrigerator. However, doing this without a cooling system and oil is dangerous: the compressor will burn out in a few minutes due to lack of heat removal and lubrication.
Frequently asked questions (FAQ)
Is it possible to repair a burnt compressor winding yourself?
Rewinding at home refrigeration compressor stator is not possible. This requires removing the casing (cutting and subsequent welding), removing the old winding, winding new wire of a strictly defined diameter and number of turns, as well as vacuuming and filling the system. It is easier and cheaper to replace the entire compressor.
Why does the multimeter show zero between the contacts?
A reading close to zero indicates a short circuit in the winding turns. This means that current flows directly, bypassing the resistance of the wire. Such a compressor is faulty and must be replaced, since when turned on it will cause a short circuit in the network or burn out instantly.
Which device is best to use for testing?
For initial diagnostics, a conventional digital multimeter is sufficient. However, for professional insulation testing (turn-to-turn short circuit and breakdown), specialists use a megohmmeter, which supplies high voltage and checks the insulation resistance under a load that simulates real operating conditions.
What to do if the winding resistances differ from the norm by 10-15%?
Small deviations can be caused by device errors or temperature. However, if the difference is significant (for example, the working winding should be 20 Ohms, but shows 5 Ohms or 50 Ohms), this is a sign of a defect. It is also important that the ratio between the starting and working windings maintains a logical proportion (the starting winding is always larger).