Many people perceive the refrigerator as a black box that just hums somewhere in the kitchen and keeps food fresh. However, if you look inside this unit, you will find a very complex engineering system, the heart of which is a compressor, often called a motor in everyday life. It is this unit that is responsible for circulating the refrigerant, creating the necessary pressure to cool the chambers. Understanding what exactly is hidden under the metal casing will help equipment owners better navigate the causes of breakdowns and communicate more effectively with technicians.
Inside this sealed unit, electrical energy is converted into mechanical energy, and then into heat, which is discharged outside. Compressor works in extreme conditions, withstanding high temperatures and pressure. In this article, we will analyze the internal structure in detail, explain the principle of operation of various types of mechanisms, and tell you how to determine the malfunction by the nature of the sound or lack of startup. Knowing the design is the first step to competent operation of household appliances.
Main components of a sealed case
Externally, the compressor is a massive metal tank, usually black, located in the lower rear part of the refrigerator. Inside this casing, which is welded from two hemispheres, there is absolute tightness. This was not done by chance: inside there is refrigerant a special oil that lubricates the rubbing parts. Depressurization of the housing almost always means the need to replace the unit, since the factory soldering at home is irreparable.
The central element of the design is electric motor, which drives the piston group or other gas compression mechanism. The engine consists of a stator mounted on springs or rubber shock absorbers, and a rotor that rotates inside it. This entire system is suspended inside the casing to minimize vibrations transmitted to the refrigerator body. If you hear a loud knocking sound during operation, one of the mounting springs may have broken.
The most important safety element is the starting and protective relay, which is often mounted externally on the winding terminals, but is electrically part of the motor starting system. It is this small block that takes the shock of a current overload and protects the windings from combustion. Inside, in an oil bath, there are rubbing vapors that require constant cooling and lubrication.
Internal structure of the electric motor
The heart of any refrigeration compressor is an asynchronous AC motor. Its design is quite reliable, but requires compliance with certain operating conditions. The basis consists of stator a stationary part with copper windings that creates a magnetic field. When voltage is applied, electromagnetic induction occurs, which causes the rotor to rotate.
The rotor, or armature, is a set of metal plates mounted on a shaft. The shaft, in turn, transmits rotational motion to the crank mechanism. It is important to notethat the shaft does not have direct contact with the housing, it rotates in plain bearings or ball bearings, which are constantly washed with oil. Lack of lubrication leads to instant scuffing of the shaft and motor wedge.
- ⚡ Starting winding —creates the initial torque to start the rotor, works only for a fraction of a second.
- 🌀 Working winding —supports engine rotation in normal mode, occupying most of the stator slots.
- 🛡️ Thermal relay - opens the circuit when the housing or windings are critically heated, preventing fire.
The motor windings are made of copper wire coated with varnish. If overheated, the varnish may burn out, which will lead to an interturn short circuit. In this case, the engine hums, but does not start, or the machine in the control panel knocks out. Diagnostics of the windings is carried out with a multimeter by measuring the resistance between the contacts.
⚠️ Attention: An attempt to independently open the sealed compressor casing without special equipment and welding skills will lead to complete loss of the unit. Residual pressure and refrigerant vapor may remain inside.
Refrigerant compression mechanism
If the electric motor creates movement, the mechanical part turns it into gas compression. Most household refrigerators use a piston system. A crank is installed at the end of the shaft, which converts the rotational movement into the translational movement of the piston. The piston moves inside the cylinder, sucking in freon vapors and compressing them.
The compression process is accompanied by heating, so the efficiency of heat removal is critically important. The high-pressure compressed gas is forced through the discharge valve into the condenser (the grille at the back of the refrigerator). At this time, a vacuum is created in the cylinder, and a new portion of refrigerant from the evaporator enters through the suction valve. This cycle is repeated dozens of times per minute.
The valve plates are made of thin elastic steel. Over time, the metal can become tired, and when moisture enters the system, it can oxidize. Deformation of the valves leads to the compressor operating, but not creating the required pressure. As a result, the chamber is warm, although the motor hums continuously.
Lubricating and cooling system
There is always a certain amount of special compressor oil inside the compressor casing. It is located in the lower part of the housing (the “crankcase”) and is necessary for lubrication of rubbing parts: piston, cylinder, shaft bearings. The oil has special properties: it does not freeze at low temperatures and does not lose viscosity when heated.
Lubrication is carried out by splashing or under pressure. Rotating parts are dipped in oil or supplied through channels to friction units. Lack of oil or its insufficient level (for example, due to leakage through a leaky casing) leads to dry friction. The metal begins to heat up, expand and eventually jam the mechanism. This is one of the most common reasons for the failure of old refrigerators.
| Parameter | Normal condition | Signs of malfunction |
|---|---|---|
| Casing temperature | Hot (up to 90°C) | Red-hot or icy |
| Operation sound | Uniform humming | Knocking, clanging, intermittent hum |
| Cyclicity | Work 10-20 minutes, rest 20-40 minutes | Works without stopping or frequent starts |
| Vibration | Barely noticeable | Strong shaking of the refrigerator body |
The motor itself is cooled by washing the body with air and heat transfer through the walls of the casing. That is why it is strictly forbidden to block air access to the back wall of the refrigerator or cover the appliances with blankets. Overheating reduces the service life of the oil and winding insulation.
☑️ Checking the condition of the compressor
Inverter technologies versus classics
Traditional compressors operate on the principle of “turned on - cooled - turned off”. This creates peak loads on the network and mechanics at each start. There are no complex electronics inside such a motor; control is carried out via a relay. However, modern models are increasingly equipped with inverter compressors.
Inside the inverter motor the operating principle is different. The electric motor here does not stop completely, but only changes the speed of rotation of the rotor. A built-in or external control unit that converts the current is responsible for this. This allows you to maintain the temperature more accurately and quietly. Additional rotor position sensors can be used inside such a device.
Why are inverters quieter?
The absence of constant start and stop cycles eliminates the loudest moment of operation - starting the engine. The motor operates in a smooth, low-frequency mode.
Inverter systems are sensitive to voltage drops in the network. While a classic motor can “digest” small surges, the complex inverter electronics often fail without a high-quality stabilizer. Repair of such components, as a rule, requires replacing the entire control module, and not just the mechanical part.
Diagnostics and typical breakdowns
Understanding the internal structure helps to diagnose the problem by external signs. If the refrigerator hums but does not cool, most likely the problem is mechanical: the piston does not compress the gas due to broken valves or a connecting rod. If the motor is silent, but hums for a couple of seconds and clicks, the winding is burned out or the shaft is jammed.
An interturn short circuit becomes a frequent problem. In this case, the resistance of the windings drops, the current increases, and the thermal relay opens the circuit. After cooling, the relay closes again and the cycle repeats. This is clearly audible: humming - clicking - silence - humming.
- 🔥 Overheating - caused by contamination of the condenser at the back or a malfunction of the fan (if any).
- 🔨 Water hammer - liquid freon entering the cylinder instead of gas, which leads to valve failure.
- 🔌 Breakthrough to the body - insulation failure, life-threatening, requires immediate disconnection.
⚠️ Attention: If you feel a tingling current when touching the body of the refrigerator, immediately disconnect the device from the network. This is a sign of poor insulation inside the motor or wiring. The operation of such a device is prohibited.
For accurate diagnostics, technicians use a pressure gauge station to check pressure and a tester to check the integrity of the windings. At home, you can only visually assess the condition and measure the resistance of the contacts, but even this requires caution.
Frequently asked questions (FAQ)
Why is the compressor hot, is this normal?
Yes, this is absolutely normal. As the gas is compressed, the temperature inside the cylinder rises very high. During active operation, the compressor casing can heat up to 70-90 degrees Celsius. You should be concerned if it is red hot or, conversely, icy when the engine is running.
Is it possible to replace the compressor yourself?
Theoretically, yes, but this requires special tools: a pipe cutter, a torch for soldering copper pipes, a vacuum pump to remove moisture from the system and a charging station. Without evacuation, the system will quickly fail due to moisture and air.
How many years does a refrigerator motor last?
The average service life of modern compressors is from 10 to 15 years. Manufacturers often advertise inverter models with a service life of up to 20 years, but the actual figure depends on the quality of the voltage in the network and operating conditions (room temperature, cleanliness of the capacitor).
What does it mean if the motor hums, but does not start?
This is a sign that the rotor cannot turn. Reasons: jamming of the mechanical part (wear, lack of oil), interturn short circuit in the windings or malfunction of the starting relay. In the latter case, repairs will be the cheapest.