When the refrigerator stops cooling or starts humming with a vengeance, most owners immediately think about the “engine”. However, a technically competent approach requires clarification: household refrigeration units do not have the usual electric motor with a rotating shaft, like in a washing machine or fan. Instead, it is used hermetic compressor, which is a complex electromechanical unit that works on the principle of reciprocating piston movement. Understanding the internal architecture of this device is critical for proper diagnosis and safe repair.
Inside the metal casing that we see at the back of the refrigerator is a whole world of mechanics and electricity. There, the refrigerant is compressed, moves through the system and lubricates the rubbing parts. Refrigerantcirculating inside is under high pressure, and the electrical windings operate in an aggressive environment of freon vapor and refrigeration oil. Any intervention requires a clear understanding of where the electrical part ends and the hydraulic part begins.
This article will reveal in detail the internal structure of the compressor, explain the functions of each element and help to understand why independent reassembly of this unit often becomes economically impractical. We will look at both classic piston models and more modern inverter systems, which radically change the approach to cooling products.
The design of the sealed casing and its purpose
The first thing that catches your eye when examining the back panel of the refrigerator is the black metal “barrel”. It sealed housingis made of stamped steel. Its main task is to ensure absolute isolation of internal components from the external environment and prevent refrigerant leakage. Inside this casing there is a vacuum or pressure (depending on the phase of operation), and oil and freon vapors fill the free space, protecting electrical contacts from oxidation.
Disassembling such a housing at home is almost impossible without specialized equipment. To open it, you either need to carefully cut off the weld seam with a grinder, or drill out the rivets, which breaks the factory seal. After repair, the housing must be argon welded again, which turns the procedure into an expensive production process. That is why compressors are considered non-repairable units in domestic conditions.
⚠️ Attention: It is strictly forbidden to open the sealed compressor casing without a license to work with ozone-depleting substances and appropriate pumping equipment Freon. This is life-threatening and illegal.
The walls of the casing also serve as a heat exchanger. During operation, the motor heats up, and the metal gives off some of the heat to the environment, although the main heat removal occurs through the capacitor (the black grille at the back). Inside the casing there are two main blocks: an electric motor and a mechanical compressor group, which we will consider in more detail.
Electrical part: stator, rotor and start relay
The heart of the device is electric motor, which converts electrical energy into mechanical movement. It consists of a stator mounted on springs inside the casing, and a rotor mounted directly on the compressor shaft. The stator windings are made of copper wire with heat-resistant insulation, since the temperature inside the operating unit can reach 100°C and higher.
To start the engine, a special starting winding is used starting relay. In older models, this relay can be made in the form of a “pill” (posistor) or an electromagnetic switch. It is this small element that often causes the refrigerator to hum but not start. The relay supplies increased current to the starting winding, creating the necessary torque to break the piston from its place.
In modern inverter models, the design of the electrical part is radically different. There is no classic start relay, and the rotation speed is controlled by complex electronics located in a separate control unit. This allows you to smoothly regulate power, reducing energy consumption and noise levels.
Why does the winding burn out?
The winding most often burns out due to a violation of the heat sink conditions (the capacitor at the rear is clogged) or voltage surges in the network. Also, the cause may be an interturn short circuit caused by aging of the insulation or moisture ingress during poor-quality repairs.
Mechanical part: crank mechanism
If you look into the lower part of the disassembled compressor (hypothetically), we will see a classic crank mechanism. The engine shaft rotates and drives a connecting rod, which pushes the piston up and down inside the cylinder. This design is familiar to anyone who has ever seen how a car’s internal combustion engine works, only the scale here is much smaller.
The piston and cylinder are manufactured with microscopic tolerances. The gap between them is calculated in hundredths of a millimeter. This is necessary to create high pressure when compressing the gas. Any scratch or scoring on the surface of the piston leads to a drop in compression and, as a result, to the inability of the refrigerator to maintain a low temperature. Lubrication of these parts occurs by splashing oil, which is located at the bottom of the casing.
The most important elements of mechanics are valves. They are located at the end of the cylinder and act as automatic dampers. When the piston goes down, the suction valve opens and freon vapor from the evaporator is sucked into the cylinder. When the piston moves upward, the suction valve closes, the discharge valve opens, and gas under pressure goes into the condenser.
☑️ Signs of mechanical failure of the compressor
Lubricating system and the role of refrigeration oil
There is a special one inside the engine refrigeration oil. It performs several critical functions: lubricates rubbing pairs (piston-cylinder, shafts), removes heat from heating parts and ensures tightness of gaps. Unlike motor oil in a car, refrigeration oil has a unique chemical compatibility with refrigerants and the ability to dissolve in them without losing its properties.
The lubrication system in most household compressors is spray. The lower end of the crankshaft often has a special scoop or screw thread. When the shaft rotates, oil is captured and sprayed along the inner walls of the casing, getting onto all moving parts. The oil level is strictly regulated by the manufacturer.
The critical point is that when the refrigerator is idle for a long time (more than 6 months), the oil drains into the system, and when suddenly started, the compressor can run dry for the first time seconds, which causes wear. That is why, after transportation or a long period of inactivity, the refrigerator must stand vertically for at least 4-8 hours before turning it on.
Table: Comparison of types of compressors
To better understand the differences in the device, consider the comparative characteristics of the main types of engines used in modern refrigeration technology.
| Characteristics | Usual (Start-Stop) | Inverter | Linear |
|---|---|---|---|
| Operating principle | On and off at full power | Smooth change in rotation speed | Rectilinear movement of the piston without rotation |
| Noise level | Medium/High (relay clicks) | Low | Very low |
| Energy consumption | High (inrush currents) | Low (savings up to 30%) | Very low |
| Resource | Standard | High (fewer start-stop cycles) | High (fewer rubbing parts) |
As can be seen from the table, the evolution of engines is aimed at reducing the number of moving parts and eliminating sudden starting loads. Linear compressors, for example, generally lack a crank mechanism, which makes their design simpler, but repair of such components is possible only in the factory.
Fault diagnosis: what can be determined from the outside
Despite the tightness of the housing, an experienced technician can tell a lot about the condition of the “internals” by external signs. If the engine hums, but does not start, and after a few seconds a click is heard, most likely the problem is start relay or jamming of the piston group. If the motor runs continuously without turning off, but the temperature in the chamber does not drop below +10°C, this indicates a loss of performance (wear of valves or piston group).
Another important indicator is the body temperature. Normally, the lower part of the casing (where the oil is) is warm, and the upper part (where the gas is pumped) is hot. If the entire compressor is so hot that it cannot be touched, this is a signal of overload, thermostat failure or refrigerant leak.
⚠️ Attention: If you smell a burning smell or see sparking in the area of the compressor terminal box, immediately unplug the device. This can lead to a fire in the plastic elements of the refrigerator.
Why engine repair is often replaced by replacement
Many users wonder: why can’t they just replace a burnt winding or bore the cylinder? The answer lies in economics and technology. Restoring tightness, evacuation of the system, charging the exact amount of oil and refrigerant, as well as soldering copper tubes require expensive equipment (vacuum pump, scales, pressure gauge station).
The cost of a new compressor is often comparable to the cost of all work to restore the old one, but the new unit will have a factory warranty and a full service life. In addition, modern engines are becoming increasingly complex in electronic control, and finding compatible spare parts for overhauling a specific unit is becoming almost impossible.
Frequently asked questions (FAQ)
Is it possible to replace the compressor on a refrigerator yourself?
Theoretically, this is possible if you have the skills to solder copper tubes with hard solder, a vacuum pump and a set of tools for charging freon. However, without experience, there is a high risk of poor-quality soldering (leakage) or incorrect dosage of oil, which will lead to rapid failure of the new compressor.
Why does the compressor knock heavily during operation?
The knocking can be caused by several reasons: weakening of the internal springs of the motor suspension, wear of the crankshaft bearings, water hammer (liquid freon entering the cylinder) or mechanical destruction of the valve group. In any case, a strong knock is a sign of imminent failure of the unit.
What pressure does the refrigerator engine create?
The pressure in the system depends on the type of refrigerant and the ambient temperature. On the discharge side (exit from the compressor), the pressure can reach 15-20 atmospheres (bar), and on the suction side it can be close to vacuum or be 1-2 atmospheres in operating mode.
Is it possible to use a compressor from a refrigerator for other purposes (for example, airbrushing)?
Yes, many craftsmen make it from old refrigerators compressors for inflating tires or airbrushing. However, to do this, it is necessary to remove all internal electrics (relays, thermal protection), remove the pipes and be sure to install a receiver (tank for air) and a moisture separator, since the refrigeration compressor pumps oil along with air.