The failure of a refrigeration unit is always stressful for the owners, because food supplies are at risk. Often the cause of the breakdown is compressor on hand, which stops starting or works intermittently. Before calling a technician or buying new equipment, it makes sense to conduct an initial diagnosis of the electrical part of the motor. This does not require complex equipment, it is enough to have a regular multimeter.
In this article we will analyze in detail the process of checking the integrity of the windings, identifying short circuits and breakdowns to the housing. You will learn to correctly interpret the instrument readings and understand whether it is worth trying to repair the unit or whether it needs to be replaced. Competent diagnostics will save you time and money, allowing you to accurately determine the nature of the malfunction.
Preparation for diagnostics and safety measures
Any work with electrical equipment requires strict adherence to safety precautions. The refrigerator operates from a 220 Volt network, which poses a real threat to life if handled carelessly. Before starting the test, make sure that the power cord is completely unplugged. Don't rely solely on the switch or thermostat—there must be a physical break in the circuit.
You will need access to the compressor, which is usually located at the bottom rear of the refrigerator. Remove the protective cover, if any, and gain access to the start-protective relay and motor contact group. To work, you will need a digital or dial multimeter, a screwdriver and, possibly, pliers.
⚠️ Attention: If you see obvious traces of burning insulation, melted wires, or smell a persistent burning smell, further self-diagnosis can be dangerous. In such cases, it is better to immediately contact service.
Check the probes of your measuring device for insulation integrity. If there are cracks in the tester's wires, it cannot be used. Set the mode switch to the resistance measurement position (Ohms), usually indicated by the symbol Ω.
Removing the starting relay and accessing the contacts
To ring the windings, you need to gain direct access to the contact terminals of the compressor. They are covered with a plastic housing for the starting and protective relay. Carefully remove this box, having first memorized or photographed the wiring diagram.
On the contact group you will see three terminals forming a triangle. Depending on the refrigerator model (for example Indesit, Atlant or LG), the markings may differ, but the principle of contact arrangement is the same. They are usually designated by the letters C, S, R or numbers.
Deciphering the compressor contacts
C - Common (common), S - Start (starting winding), R - Run (working winding). Sometimes, instead of letters, the numbers 1, 2, 3 are used, where 1 is starting, 2 is working, 3 is general.
Clean the contacts from oxides and dust with a dry cloth. Oxidation can distort meter readings, giving the false impression of resistance where there shouldn't be any. After preparation, you can begin measurements.
Determination of the type of windings and wiring diagram
The refrigerator motor is asynchronous and has two main windings: working and starting. The working winding is made of thicker wire and has less resistance, and the starting winding is made of thin wire and has higher resistance. The third pin is common to both circuits.
First you need to determine which of the three pins is common. Place the multimeter probes on any pair of contacts and record the readings. Then change the combination. You need to find a pair where the resistance is maximum. Two contacts not participating in this maximum value will be working and starting, and the third (remaining) will be common.
- 🔌 Common contact (C): the point against which the resistance of other windings is measured.
- 🚀 Starting winding (S): has the highest resistance, is turned on only at the time of start.
- ⚙️ Working winding (R): has an average resistance and ensures constant operation of the motor.
The ratio is considered normal in which the sum of the resistances of the starting and working windings is equal to the resistance between the extreme contacts (without a common one). If you see values in the range from 10 to 40 Ohms for the working winding and up to 60 Ohms for the starting winding, this is a good sign.
Search for open circuits and short circuits
The most common cause of compressor failure is an open circuit inside the winding or an interturn short circuit. If the multimeter shows infinity (one in the most significant digit or an overload symbol) when testing any of the windings relative to the common contact, it means that a break has occurred break.
It is impossible to restore a break inside a sealed case. This engine must be scrapped or replaced. If the device shows zero or a value close to zero, this indicates a short circuit of the turns. In this case, the motor will get very hot and knock out the circuit breaker.
Below is a table with approximate resistance values for serviceable compressors of various capacities:
| Winding type | Normal resistance (Ohm) | Symptom malfunction |
|---|---|---|
| Working (Run) | 10 - 25 Ohm | ∞ (break) or 0 (short circuit) |
| Start | 20 - 45 Ohm | ∞ (break) or 0 (short circuit) |
| Between contacts | Sum of R and S | Significantly less than the sum |
Checking for insulation breakdown (case to ground)
The situation is particularly dangerous when a phase gets on the metal housing of the compressor. This may result in electric shock if you touch the refrigerator. You can check for an insulation breakdown (“to ground”) using a multimeter by switching it to the diode continuity mode or measuring resistance to the maximum limit.
Press one probe to any of the three contacts of the connector (after making sure that they are not shorted to each other), and with the second touch the place on the metal body of the compressor that has been cleared of paint. It is best to clean a small area with a wire brush or sandpaper to ensure reliable contact.
If the device is silent or shows one (infinite resistance), the insulation is intact. If you hear a squeak or see low resistance values, then something has happened casing breakdown. It is strictly prohibited to operate such a refrigerator.
⚠️ Attention: Even if the compressor starts, but has a casing breakdown, its use is deadly. The leakage current may not knock out the machine, but will create a voltage on the body sufficient to cause death.
Sometimes breakdown occurs only when heated or vibration. If there is no breakdown when the engine is cold, but the RCD (residual current device) knocks out during operation, this is a sure sign of deterioration in the insulating properties of the windings.
Diagnostics of the starting relay and thermal protection
Often the engine itself is working, but does not start due to a malfunction of the attachment. The starting relay is responsible for short-term connection of the starting winding, and the thermal relay protects the motor from overheating. They can also be checked with a tester.
Remove the relay from the compressor contacts. Shake it: if it rattles inside, it means the core or contacts are broken, and the relay needs to be replaced. Ring the relay contacts in different positions. The resistance of the solenoid coil (if the relay is electromagnetic) should be within normal limits, and the contacts in the closed state should show zero.
☑️ Checklist for checking the relay
The thermal relay (tablet) in a cold state should ring (show zero). If it does not ring, it means that the circuit is broken and the current does not reach the motor windings. Replace this element with one similar in response current.
Analysis of results and further actions
After all measurements have been carried out, it is necessary to systematize the data. If all three contacts have a resistance within acceptable limits and there is no breakdown to the housing, the electrical part of the engine is working properly. In this case, the problem may lie in the mechanical part (jamming of the piston group) or in the refrigerant system.
If a break, short circuit or breakdown in the housing is detected, the compressor requires replacement. Attempting to rewind the engine at home is impractical due to the need to seal and evacuate the system.
When replacing a compressor, it is important to take into account the refrigerant for which the system is designed (R134a, R600a) and the power of the motor. An incorrectly selected unit will lead to inefficient operation of the refrigerator or rapid failure of the new unit.
Remember that to replace the compressor you will need a special tool: a burner, a vacuum pump and a pressure gauge station. If you do not have experience working with copper tubes, it is better to entrust the final stage to professionals.
Is it possible to check the compressor without removing the relay?
Theoretically, you can try to ring the contacts through the relay connector, but this will not give a 100% guarantee of accuracy due to the possible resistance of the contacts of the relay itself. For reliable diagnostics, it is better to remove the relay and call the terminals on the motor housing directly.
Why does the multimeter show different values with each measurement?
The resistance of the windings depends on the temperature of the copper. If the engine is warm, the resistance will be higher. Also, the readings can be affected by oxidized probes or poor contact with the terminals. Let the motor cool and clean the contacts.
What to do if the resistance of the windings is normal, but the motor hums and does not start?
Most likely, the piston group is jammed or there is no starting torque due to a malfunction of the capacitor (if it is in the circuit) or the starting relay. In rare cases, “wedging” by applying increased voltage helps, but this is a risky procedure.
Which multimeter is better to choose for repairing refrigerators?
For household repairs, any digital multimeter with a continuity function and measuring resistance up to 2000 Ohms is suitable. Professionals may need models with the function of measuring capacitor capacity and current clamps.