A sudden stop of the refrigerator often becomes an unpleasant surprise, especially when there are perishable foods inside. First of all, owners begin to look for the cause, and most often suspicions fall on the compressor, which in everyday life is often called an electric motor. It is this unit that ensures the circulation of the refrigerant, creating the necessary cold in the chambers.
Before calling a technician or buying new equipment, it makes sense to carry out the initial diagnostics yourself. Checking the electric motor does not require complex equipment, but requires accuracy and attention to detail. Understanding the principle of operation of the compressor will help you save time and money, as well as accurately describe the problem to a specialist.
In this article we will look at the basic testing methods, look at typical faults and learn how to use measuring instruments. You will learn how to distinguish a motor failure from problems with the start relay or thermostat. A competent approach to diagnostics is half of a successful repair.
Operating principle and structure of the compressor
The electric motor of a refrigerator is a sealed unit, inside of which there is an electric motor and a piston group. Unlike conventional motors, it operates in an environment of inert gas and oil, which eliminates the possibility of direct lubrication or replacement of brushes. Asynchronous motor Inside the casing it has two main windings: starting and working. Their interaction creates a rotating magnetic field that starts the rotor.
The key element of the starting system is start relay, which supplies an impulse to the starting winding only at the moment of start. As soon as the motor reaches the required speed, the relay opens the circuit and the engine continues to operate only on the working winding. Malfunction of any of these components leads to the fact that the refrigerator stops cooling, although it may make characteristic clicks or buzzing.
⚠️ Attention: It is strictly forbidden to open the sealed compressor casing at home. Inside there is freon under pressure, as well as oil vapor. Any violation of the tightness without special equipment will make the unit unsuitable for further operation.
To understand the diagnostic processes, it is important to know that the electrical part of the motor is isolated from the housing, but over time the insulation of the windings can degrade. This leads to short circuits or breakdowns to the housing. It is these parameters that we will check using multi-MRT.
Necessary tools and safety measures
High-quality diagnostics is impossible without a basic set of tools. The main device for checking the electric motor is multimeter (tester). It will allow you to measure the resistance of the windings and check for breakdown on the housing. You will also need screwdrivers to remove the protective cover at the back of the refrigerator and pliers.
Safety is the number one priority when working with electrical appliances. Before starting any work, you must completely turn off the power to the refrigerator by unplugging the cord from the outlet. Even after disconnection, a residual charge may remain in the capacitors, so you should not touch the contacts with bare hands without first checking.
- 🔧 Multimeter - the main device for measuring resistance and circuit integrity.
- 🪛 A set of screwdrivers - for dismantling the protective casing and removing terminals.
- 🧤 Dielectric gloves —additional protection when working with electricity.
- 🔦 Flashlight —for inspecting hard-to-reach places in the engine compartment.
If you are using old analog tester, make sure it is calibrated. Digital multimeters are more convenient to use and give accurate readings. Also prepare a notepad to record instrument readings, as they can easily be confused during operation.
Visual inspection and initial diagnostics
The first stage of testing is always a careful visual inspection. Remove the back cover of the refrigerator at the bottom where the compressor is located. Pay attention to the appearance of the unit: there should be no traces of oil, severe corrosion or mechanical damage. The presence of oil smudges often indicates depressurization of the system.
Check the condition of the starting relay and capacitor. The relay is usually mounted on the side or top of the compressor and has a plastic housing. If traces of melting, burning or cracks are visible on the relay body, this is a sure sign of a malfunction. Starting capacitor It should also not have swelling or leaked electrolyte.
Inspect the wiring for kinks, melted insulation, or signs of rodent activity. Often the problem lies not in the motor itself, but in a broken contact in the power circuit. If no visual defects are detected, we proceed to a deeper check using instruments.
Checking the starting relay and thermal protection
Before “sinning” on the electric motor itself, it is necessary to exclude a malfunction of the starting relay and thermal protection relay. These components cost less and fail more often. Remove the relay from the compressor contacts by disconnecting the retaining clips. Carefully disassemble the relay housing, if possible, or prepare to test the entire circuit.
Using a multimeter in continuity mode, check the integrity of the contacts. For a thermal relay, the resistance should be close to zero when cold. If the device shows infinity (open), then the circuit is broken and no current flows to the motor windings. In this case, the motor will not start, even if it is fully operational.
How does thermal protection work?
The thermal relay opens the circuit when the compressor overheats or when there is excessive current consumption. Inside there is a bimetallic plate that bends when heated and opens the contacts. After cooling, it should return to its original position.
Also check the condenser if it is placed separately. It must accumulate and release charge. On a multimeter with a capacitor testing function, its capacitance should correspond to the marking. In resistance measurement mode, the needle of the analog device should deviate and gradually return back.
⚠️ Attention: When checking the relay, be careful with the contacts. Do not forcibly close them with your fingers or live tools - this can lead to a short circuit and damage to the motor windings.
Diagnostics of the motor windings with a multimeter
This is the most important stage of diagnosis. To carry out the test, it is necessary to gain access to three contacts on the compressor housing. They are usually arranged in a triangle. Remove the start relay to clear the contacts. On many models, the contact layout is marked on the relay cover or housing, but it is better to know the standard markings: Common (C), Run (R) and Start (S).
Switch the multimeter to resistance measurement mode (Ohms). First, find a common contact. Measure the resistance between each pair of contacts. The pair with the lowest resistance is the run and start windings together, and the third contact not involved in this pair with the lowest value is often common. However, it is easier to measure all three pairs:
| Pair of contacts | Normal resistance | What does it mean |
|---|---|---|
| Working - Common | 10–30 Ohm | Main winding |
| Starting winding - Common | 20–50 Ohm | Starting winding (above the working winding) |
| Working - Starting | The sum of the two is higher | Serial connection |
| Any - Housing | Infinity (∞) | No breakdown to ground |
If the multimeter shows infinity (one in the most significant digit) between the windings, it means in the motor open circuit. This often occurs due to the burnout of the thin wire of the starting winding. If the resistance is close to zero, then interturn short circuithappened. In both cases, the electric motor cannot be repaired and requires replacement.
☑️ Algorithm for checking windings
Pay special attention to checking for breakdown of the housing. Touch one probe to any contact, and the other to the stripped metal part of the compressor housing (where there is no paint). The device should show infinity. Any resistance value indicates an insulation failure, which is deadly and requires immediate replacement of the unit.
Checking the current strength and power consumption
If the winding resistance is normal, but the refrigerator still does not work or often turns off, you need to check the current strength during startup and operation. To do this, you will need a current clamp or an ammeter connected to the open circuit. The normal operating current for household refrigerators is from 0.5 to 1.5 Amperes, depending on the power of the model.
At the moment of startup, the current may briefly jump to 3–5 Amperes, but then it should drop to the nominal value. If the starting current significantly exceeds the norm and the thermal protection immediately triggers, this is a sure sign turn-to-turn short circuit in the windings or mechanical jamming of the piston group. It is impossible to operate such a motor.
It is also worth checking the voltage in the network. Low voltage (below 190V) may prevent the compressor from starting, causing humming and overheating. In such cases, it is recommended to use a voltage stabilizer. High voltage is also harmful to the insulation of the windings.
Typical faults and methods for eliminating them
Based on the diagnostics, several scenarios can be identified. If the windings ring, but the motor does not start, but only hums, most likely the piston group is jammed or the starting relay has failed. Sometimes the “boost” method helps (applying increased voltage to the starting winding), but at home this is risky and requires a special transformer.
If a break or short circuit in the windings is detected, the output is compressor replacement. Repairing windings in a sealed housing is not economically feasible and technically difficult. When replacing, it is also important to replace the filter drier and evacuate the system, which requires professional equipment.
- 🔥 Overheating - often caused by contamination of the condenser at the back of the refrigerator. Simple cleaning with a vacuum cleaner can solve the problem.
- 🔌 Loosening the contacts - oxidized terminals heat up and melt the relay. Cleaning the contacts restores operation.
- 🛑 Jagging —if the motor hums and knocks out the protection, the piston may be jammed. Sometimes gently tapping the body of a running motor with a hammer helps (a risky method).
Do not forget that modern inverter compressors are diagnosed differently. They cannot be checked by simply ringing the windings, since they are controlled by a complex electronic unit. To diagnose inverters, a connection through a service tester is required.
⚠️ Attention: The characteristics of compressors and their diagnostic methods may vary depending on the manufacturer (Atlant, Indesit, LG, Bosch). Always check the technical documentation of a specific model before intervening.
Frequently asked questions (FAQ)
Is it possible to replace the refrigerator compressor yourself?
Theoretically, yes, if you have soldering skills copper pipes, vacuumizer and charging station. However, without special equipment, it is impossible to properly charge the system with freon and remove moisture, which will lead to rapid breakdown of the new compressor.
Why does a new compressor burn out immediately after installation?
Most often the reason is the acidic environment remaining in the system from the burned out old motor. Before installing a new unit, be sure to flush the system with nitrogen and replace the filter drier.
How to distinguish an inverter compressor from a conventional one?
Inverter models are quieter, do not have characteristic on/off clicks and smoothly regulate power. The case is often marked “Inverter”, and they are connected not through a relay, but through an electronic control unit.
Is it dangerous to touch a running compressor?
Yes, it is dangerous. The housing can heat up to 80–90 degrees Celsius, which can cause burns. In addition, if there is an insulation breakdown, life-threatening voltage may be present on the case.