Modern refrigerator is a complex electromechanical device, the core of which is a compressor. It is this unit that is responsible for circulating the refrigerant in the system, creating the necessary cold inside the chambers. When the unit stops freezing and the engine is silent or, conversely, hums but does not start, the owner is faced with the question of the need for expensive repairs or replacement of equipment. The first and most accessible stage of diagnostics is checking the electrical circuit of the motor using a household measuring instrument.
To carry out high-quality diagnostics, you will need a digital multimeterset of screwdrivers and basic knowledge of safety precautions. The verification process does not require deep engineering knowledge, but it does require care and accuracy of the instrument readings. Errors at this stage can lead to false conclusions when a working compressor is declared inoperative, or, worse, to an attempt to connect the faulty unit to the network.
In this article we will analyze in detail the algorithm of actions that will allow you to determine the condition of the motor windings. You will learn how to distinguish a working motor from a burnt one, what resistance values are normal for different models, and when the only option is to call a repairman. A competent check will save your budget from unnecessary expenses and help you make an informed decision about the fate of household appliances.
Preparation for diagnostics and safety precautions
Before you begin directly measuring the parameters of the electrical circuit, it is necessary to ensure complete safety of the work. Electric current in combination with the metal body of the refrigerator poses a real threat to life. First of all, the device must be completely de-energized: remove the plug from the socket. Do not rely only on the mains switch; physical disconnection from the power source is a must.
Next you should gain access to the compressor. In most refrigerator models Indesit, Atlant or Beko the motor is located in the lower rear part of the case. You will need to remove the protective metal or plastic cover that covers the unit and condenser grille. It is usually attached to several bolts or latches, which can be easily removed with a Phillips screwdriver.
⚠️ Attention: If the compressor has just been running, its metal parts may be very hot. Allow the refrigerator to cool for 15-20 minutes before starting work to avoid burns and damage to wire insulation from contact with hot surfaces.After removing the cover, you will see a black barrel-shaped motor housing, to which the electrical cable and copper tubes fit. We are interested in the cable connection point, which is covered with a plastic casing. Carefully remove this casing to get to the relay contact group and the starter. This is where we will take measurements.
Visual inspection and search for external defects
Before picking up the measuring device, conduct a thorough visual inspection of the unit. Often the cause of the malfunction is obvious and does not require complex calculations. Carefully examine the condition of the insulation of the supply wires. If you see melted plastic, blackening or burning marks, this is a sure sign of overheating and a short circuit in the circuit.
Inspect the compressor housing itself. There should be no swelling, oily smudges or traces of rust that has penetrated through the metal. The presence of oil around the rod or welds may indicate a violation of the tightness of the system, which makes further electrical diagnostics pointless - such a unit requires replacement as a whole.
Pay special attention to the contact group. Oxidized or blackened contacts of the start relay often cause the engine to not start, although the engine itself is fully operational. If you find carbon deposits, you can carefully clean it with fine sandpaper, but it is better to immediately replace the starting relay, since its resource may have been exhausted.
How to distinguish traces of oil from condensation?
Oil has a characteristic odor and a greasy structure; it does not evaporate. Condensation is water, it is transparent, odorless and does not leave a greasy residue when it dries. Wipe the suspicious area with a dry cloth: if there is a greasy stain left, this is freon oil, which means that the tightness of the circuit is broken.
Setting up a multimeter and a breakdown test
To work, we need a resistance measurement mode, which is indicated on the instrument panel by the symbol
Ω(Ohm). If your multimeter does not have automatic range selection, set the range to 20 kΩ or 200 kΩ. Before starting measurements, make sure that the probes are in good condition: connect them to each other, the device should show a value close to zero.The first and most important stage is checking for insulation breakdown (short circuit to the housing). This is critical for the safety of further operation. Set the multimeter to continuity mode (often indicated by a speaker symbol) or resistance measurement to the maximum limit.
Press one probe to any copper outlet pipe of the compressor or to an unpainted metal part of the housing (you can first clean a small area with a knife until it shines). With the second probe, touch each of the three contacts on the motor terminal block in turn.
The normal insulation resistance between the windings and the housing should tend to infinity, any values below 1 MOhm (MegaOhm) are considered critical and indicate damage to the winding.
- 🔌 If the device is silent or shows one (infinity) - the insulation is intact, you can continue the diagnosis.
- 🔥 If a beep is heard or the resistance reading is close to zero, a breakdown has occurred to the housing.
- ⚡ In the event of a breakdown, the operation of such a refrigerator is mortally dangerous, the motor must be disposed of.
Measuring the resistance of the working windings
After successfully passing the breakdown test, we move on to the main part of the diagnosis - measuring the resistance of the windings themselves. A standard single-phase compressor has three terminals: two for the work windings and one for the common point. Our task is to find these terminals and measure the resistance between them.
Remove the start relay and protective casing to free the three contacts going to the motor. They are usually arranged in a triangle. We need to ring them in pairs. Set the multimeter to resistance measurement mode at the 2 kOhm limit (2000 Ohms). This will give you the most accurate readings for low resistances.
Measure the resistance between the first and second terminals, then between the second and third, and finally between the first and third. Record all three values obtained. In a working engine, you will get three different values (or two close ones and one equal to their sum), which should fall within certain ranges.
📊 What readings did your multimeter give when testing the windings?The readings are within normal limits (tens of ohms)The resistance is infinity (break)The resistance is zero (short circuit)The device behaves unstableThe typical picture for a working motor looks like this: between two contacts the resistance is minimal (this is the starting winding), between the other two - a little more (working winding), and between the remaining ones - the sum of the two previous ones values. For example, if there are 20 Ohms between 1-2 contacts, and 40 Ohms between 2-3 contacts, then between 1-3 there should be about 60 Ohms.
If you see a unit in the most significant digit on the multimeter screen (for example,
1.orOL), this means an open circuit. The break can be internal (the winding is burned out) or external (poor contact inside the terminal box). In any case, such a motor will not start on its own.☑️ Algorithm for checking the windings
Done: 0 / 6Analysis of the obtained data and table of standards
Interpretation of the obtained figures requires an understanding of the specifics of different types of compressors. The power of the motor directly affects the resistance of its windings: the more powerful the motor, the thicker the winding wire and the lower its resistance. Therefore, the values for a small refrigerator and a powerful two-chamber unit will be significantly different.
Below is a table with approximate resistance values for compressors of various capacities. Remember that the permissible measurement error with a household multimeter can be up to 10-15%, and the resistance of the windings also depends on the engine temperature (cold or warm).
Compressor power Starting winding resistance (Ohm) Working winding resistance windings (Ohm) Total resistance (Ohm) Up to 100 W 25 – 35 35 – 45 60 – 80 100 - 150 W 15 – 25 20 – 30 35 – 55 150 - 200 W 10 – 18 12 – 22 22 – 40 More than 200 W 5 – 12 8 – 15 13 – 27 It is important to consider that in inverter compressors, which are often found in models LG or Samsung recent years, the operating principle is different. It uses a three-phase motor, and the resistance between the windings must be exactly the same. Any difference in the readings for the inverter motor indicates its malfunction.
It is also worth noting that the resistance can “float” when heated. If you carried out a series of measurements and the values began to change chaotically upward, this may indicate an interturn short circuit, which only appears when the winding heats up. In a cold state, such a defect may not be noticed.
What is an interturn short circuit?
This is damage to the insulation between the turns of the wire inside the winding. In this case, the total resistance may change slightly, but the current in the circuit will increase sharply, causing the thermal relay to operate or the motor to hum without starting. It is difficult to detect a 100% interturn short circuit with a multimeter; current clamps are often required.
Frequent diagnostic errors and their consequences
One of the most common mistakes is ignoring the state of the multimeter probes. If the ends of the probes are oxidized or the wires inside them are broken at the base, the device will show incorrect values. Always check the probes by shorting them together before measuring - the resistance should be minimal.
Another mistake is taking measurements on a device connected to the network. This will not only cause the multimeter's fuse to instantly blow, but may also cause serious electrical injury. Always double-check that the device is unplugged from the outlet before touching the contacts with probes.
Some technicians try to assess the condition of the motor “by ear” or by temperature, neglecting instrumental diagnostics. However, as practice shows, visual signs are often deceptive. The compressor may be cold and quiet, but have an internal break, which is visible only on the tester screen.
⚠️ Attention: Do not try to start the compressor directly, bypassing the relay, if you are not sure that the windings are working properly. If a short circuit occurs inside, direct connection to a 220V network can cause popping, sparking and damage to the wiring in the apartment.It is also worth remembering that manufacturers are constantly improving designs. New models may use specific connectors or built-in control modules. If you see that there are not three wires coming from the compressor, but a complex chip with many contacts, it is better to check the technical documentation of the specific model.
Frequently asked questions (FAQ)
Is it possible to check the compressor without removing it from the refrigerator?
Yes, in most cases this is possible. You just need to remove the back cover and the contact cover. However, if a leak test or oil change is required, the compressor will have to be completely dismantled.
What to do if the winding resistance is zero?
If the multimeter shows 0 Ohm between the contacts, this means a short circuit inside the winding. Such a motor is burnt out and cannot be restored; it needs to be replaced with a new one.
Why does the multimeter show infinity, although the motor is humming?
This indicates an open circuit. A humming noise may be caused by an attempt to start through the start relay, but no current flows due to an open in the winding or poor contact inside the terminal box. Check the reliability of the connection of the wires to the motor contacts.
Does the engine temperature affect the multimeter readings?
Yes, it does. The resistance of metals increases with increasing temperature. A cold motor will show less resistance than a warm one. For accurate diagnostics, it is better to compare the readings with tabular data for a cold state.
Is it possible to use a dial tester instead of a digital one?
It is possible, but a digital multimeter is more convenient and more accurate for such measurements. When using a dial gauge, it is important to choose the correct range so that the needle does not go off scale and is in the working area of the scale.