A sudden stop in the operation of the refrigerator often becomes an unpleasant surprise that requires immediate attention. If the unit stops humming and the temperature in the chambers begins to rise rapidly, the compressor is usually the first suspect. It is this unit that is responsible for the circulation of the refrigerant, and its failure will paralyze the entire cooling system. However, you should not immediately write off the motor and plan an expensive replacement.
Before calling a technician or buying a new unit, it makes sense to conduct an initial diagnosis of the electrical part of the engine. In most cases, the reason lies in an open circuit, an interturn short circuit or a breakdown to the housing, which can be detected using a conventional multimeter. Checking the windings is a basic skill that will allow you to save time and money by accurately determining the nature of the fault.
To carry out the work you will need a minimum set of tools and basic knowledge of electrical engineering. It is important to understand that any manipulations with electrical equipment require compliance with safety precautions. Disconnecting the appliance from the network is the first and immutable rule, ignoring which can lead to electric shock or damage to the electronics of the refrigerator.
Preparation for diagnostics and safety measures
The start of any repair procedure must be accompanied by ensuring safe working conditions. Since the refrigerator operates from a household voltage of 220 volts, the risk of receiving an electric shock when opening the compressor compartment remains high. Before touching any wires or contacts, the device must be completely de-energized. Simply turning off the button on the case is not enough - be sure to remove the plug from the socket.
After turning off the power, you should gain access to the compressor, which is usually located in the lower rear part of the refrigerator. You will need to remove the protective cover covering the motor-compressor and the start-up relay. In some models of Indesit or Ariston refrigerators access may be limited by the design features of the case, so act carefully so as not to damage the plastic latches.
⚠️ Attention: If you notice marks burning, insulation melting or you feel a persistent smell of burnt plastic, it is better not to carry out further diagnostics without skills in working with electricity. Visual signs of a short circuit often indicate a serious failure in the electrical network of the device.
You will need a digital multimeter to take measurements. Make sure the device is working properly and its battery is charged. Switch the tester to resistance measurement mode (Ohms), selecting a range of up to 2000 Ohms or 2 kOhms. If your multimeter has a “continuity” function with a sound signal, this will greatly simplify the search for open circuits.
Before connecting the probes to the compressor, you must disconnect the terminal block with wires from the starting and protective relay. Typically these elements are placed directly on the compressor contacts. Carefully remove the plastic relay box to expose the three motor terminals. It is these contacts that will be the object of your research.
☑️ Checking readiness for operation
Search for a common terminal and winding diagram
Domestic refrigerator compressors are usually equipped with three terminals, forming a triangle or arranged in a row. These contacts correspond to the starting, working winding and common wire. To take measurements correctly, it is necessary to identify which terminal is common. This is a critically important stage, since incorrectly connecting the probes will lead to erroneous readings.
It is impossible to visually determine the purpose of the contacts, since they are not marked on the motor body itself. However, the pinout may be indicated on the starting relay or in the technical documentation for a specific model. If there is no documentation, you will have to use the exclusion method and measure the resistance between pairs of contacts. Danfoss or Secop compressor pinout may be indicated. If there is no documentation, you will have to use the exclusion method and measure the resistance between pairs of contacts.
Take a multimeter and alternately measure the resistance between each pair of three available contacts. Record the resulting values. The pair of contacts between which the resistance will be greatest corresponds to the sum of the resistances of the starting and operating windings. The third contact, which did not participate in this measurement (or participated in the measurements with less resistance), is the desired common terminal.
Why is it important to find the common wire?
The common wire is the reference point for all measurements. If you mistake the working terminal for the common one, the calculated resistance values of the starting winding will be incorrect, which will lead to an erroneous diagnosis of an interturn short circuit.
Once the common wire is found, the logic becomes transparent. The resistance between the common wire and one of the remaining wires will be less - this is the working winding. The resistance between the common wire and the third contact will be greater - this is the starting winding. The sum of these two values should be equal to the resistance measured between two non-common contacts.
The procedure for measuring resistance with a multimeter
Technically, the measurement process is not difficult, but it requires attentiveness and steady hands. The multimeter probes must fit tightly to the compressor contacts to eliminate the influence of the transient resistance of oxides. If the contacts look oxidized, they can be carefully cleaned with fine sandpaper before measurement.
First, measure the resistance of the working winding. We place one probe on the common terminal, the second on the terminal of the working winding (which we defined as having less resistance). Write down the value. Then we repeat the procedure for the starting winding: common terminal and the remaining third contact. Here the readings should be higher.
Particular attention should be paid to the stability of the readings. The numbers on the screen should not “jump”. If the value rises slowly or changes erratically, there may be poor contact or oxidation inside the winding that appears under current. It is also important to make sure that you do not touch the metal parts of the probes with your fingers, as the resistance of the human body can distort the result at high ranges.
In some cases, especially on older refrigerators, the resistance can be very low, close to a few ohms. In this range, even a small resistance of the multimeter probes itself plays a role. For accuracy, you can first short-circuit the probes to each other, remember the readings (usually 0.3–0.6 Ohm) and subtract this value from the result obtained.
Analysis of the data obtained and a table of norms
Having received three resistance values (between pairs of contacts), it is necessary to analyze their ratio. In a working engine, a clear mathematical relationship is observed. The resistance of the starting winding is always higher than the resistance of the working winding. The resistance ratio is usually around 1:2 or 1:3, depending on the motor design.
Below is a table to help interpret your measurements. Please note that specific numbers may differ for different models, but the principle of the relationship remains the same.
| Measurement type | Normal reading | Possible malfunction |
|---|---|---|
| Working winding | 10 – 30 Ohm | Open (infinity) or short circuit (close to 0) |
| Starting winding | 20 - 60 Ohm | Open (infinity) or short circuit (close to 0) |
| Sum of windings | Equal to the sum of the two above | Discrepancy in the sum indicates a measurement error |
| Case and winding | Infinity (1) | Insulation breakdown on the housing |
If you get a value close to one (infinity) in any of the sections, this indicates Open circuit. The winding has burned out and no current passes through it. Such a compressor cannot be repaired at home; it needs to be replaced. If the resistance is close to zero, this is a sign of a short circuit.
Diagnostics of breakdown on case
The most dangerous malfunction that can occur with an electric motor is a breakdown of the winding insulation on the metal body of the compressor. In this case, the body becomes energized, which creates a direct threat to human life upon contact. It is necessary to check for breakdown, even if the winding resistance is normal.
For diagnostics, switch the multimeter to the resistance measurement mode at the maximum limit (usually 20 MOhm or 2000 kOhm). Press one probe to any of the three contacts of the compressor (previously cleaned from varnish or paint to metal), and the second to the copper tube on the motor housing or to the unpainted metal part of the housing.
⚠️ Attention: If even the slightest resistance is detected between the winding and the housing, operation of the refrigerator is prohibited! This can lead to an electric shock when touching the body of the refrigerator or to tripping the RCD in the panel.
A working device should show one (infinity) on the screen. Any other values indicate an insulation failure. Sometimes a breakdown only appears during heat or vibration, so a static measurement may not show the problem. In such cases, more complex diagnostics using a megohmmeter is required, but for household testing a multimeter is usually sufficient.
It is worth noting that in modern refrigerators with inverter compressors the situation is more complicated. LG or Samsung inverter motors they have a different winding design and are controlled by complex electronics. The resistance of their windings can be very low (less than 10 ohms), and diagnostics require special knowledge. If you have an inverter refrigerator, it is better to limit yourself to checking for breakdown and the absence of obvious breaks.
Typical errors and hidden problems
Often, beginners are faced with a situation where all measurements are normal, but the compressor does not start. This may not be due to the windings themselves, but to the starting relay or capacitor. A start relay is an electromechanical switch that supplies voltage to the start winding only at the moment of start. If its contacts are stuck or burnt, the motor will hum but will not start.
Another common problem is an interturn short circuit, which is difficult to diagnose with a conventional multimeter. With such a defect, the winding resistance may differ from the norm by only a few ohms, which is within the error limits of the device. However, when voltage is applied, such a winding begins to heat up, the current increases, and the thermal protection relay is triggered.
Do not forget about thermal protection built into the compressor housing. It is a bimetallic plate that opens the circuit when overheated. If it is faulty or the compressor is overheated, the circuit will be open and the multimeter will indicate an open circuit. Let the motor cool for 30-40 minutes and repeat the measurements.
It is also important to check not only the motor itself, but also the wires suitable for it. It often happens that a break occurs not inside the winding, but at the place where the wire is soldered to the contact group of the compressor due to vibration or overheating. Carefully inspect the connections.
Frequently asked questions (FAQ)
Is it possible to rewind the refrigerator compressor yourself?
Theoretically, it is possible to rewind, but in practice it is not economically feasible and technically difficult. Special equipment is required for winding, laying and drying the windings, as well as sealing the housing. The cost of labor and materials often exceeds the price of a new compressor. It is easier and more reliable to replace the entire assembly.
Why does the multimeter show zero on all windings?
A reading close to zero on all pairs of contacts indicates a short circuit. This means that the insulation between the turns is completely broken and the current follows the path of least resistance. Such an engine has burned out and must be disposed of.
Does the ambient temperature affect the resistance readings?
Yes, the copper from which the windings are made changes its resistance depending on the temperature. On a cold compressor the resistance will be lower, on a hot compressor it will be higher. However, these changes are insignificant for diagnosing circuit integrity. The main thing is the absence of a break (infinity) or a short circuit (zero).
What to do if the compressor hums but does not start?
If the windings are intact, check the starting relay. Try replacing it with a known good one. Mechanical jamming of the piston group (“seizing” of the compressor) is also possible. In this case, the motor hums, consumes a lot of current, but the shaft does not turn. Attempts to start it with a “pusher” or by increasing the voltage at home are dangerous.
Is it possible to start a three-phase compressor from a single-phase network?
Domestic refrigerators are equipped with single-phase motors. If you are faced with a three-phase motor (a rarity in household appliances), to operate it in a regular outlet will require a delta or star switching circuit and the use of capacitors. However, in the context of household refrigerators, this practically does not occur.