Internal structure of the refrigerator compressor: what's inside?

Many users take a working refrigerator for granted, thinking about its internal structure only at the moment of breakdown or the appearance of extraneous noise. Behind the characteristic humming sound coming from the back of the unit is a complex mechanical process that keeps your food cold. It is compressor that is the heart of the system, forcing the refrigerant to circulate in a closed circuit.

The question of what exactly is inside this metal “boiler” worries not only inquisitive craftsmen, but also equipment owners trying to understand the cause of the malfunction. Inside the sealed case there is a vacuum filled with vapor Freon and special oil necessary for lubricating the rubbing parts. Understanding this design helps you understand why independent repairs without special equipment are often impossible and even dangerous.

Let us examine in detail the components and substances that ensure the uninterrupted operation of your household assistant.

Sealed housing and internal atmosphere

Externally The compressor is a massive metal cylinder painted black. This is not just a decorative solution, but a necessary protective measure. The body is made of durable steel and welded hermetically to eliminate any possibility of leakage of working substances. Inside this casing, a technical vacuumis created, which is filled with an inert gas mixture and refrigerant vapor.

The pressure inside the casing may vary depending on the type of compressor and the phase of operation, but it is always strictly controlled. If the seal is broken, air and moisture will get inside, which will lead to the formation of an acidic environment and rapid failure of the electrical part of the motor. That is why factory welding is a critical element that must not be damaged during diagnostic attempts.

The internal surface of the housing is often coated with an anti-corrosion compound that is resistant to the aggressive effects of oils and freon. Any damage to this layer from the inside can lead to microscopic leaks, which over time will lead to a complete loss of refrigerant.

⚠️ Attention: It is strictly forbidden to open the compressor housing at home. There may be gas under pressure inside, and oil vapors are toxic. In addition, the entry of oxygen into the system when the cooling circuit is open will instantly disable the refrigerator.

Electric motor and rotor group

The basis of the internal mechanism is an electric motor that drives the piston group. In modern household models, they are most often used asynchronous motors, operating from a standard network. They consist of a stationary stator with windings and a rotating rotor.

The rotor is mounted directly on a shaft, which is connected to the piston. When voltage is applied, the magnetic field causes the rotor to rotate, converting electrical energy into mechanical motion. The quality of winding insulation plays a decisive role here, since they are constantly in the environment of oil and freon vapors, which can be chemically aggressive in the presence of moisture.

To reduce friction and heat removal, all moving parts are immersed in oil. This ensures long service life of bearings and rubbing surfaces. If the oil loses its properties or its level drops, the engine will begin to overheat and eventually seize.

Piston group and valve system

The heart of the mechanical part is piston group, consisting of a cylinder, piston, connecting rod and crankshaft. This is where the compression of freon gas occurs. The piston moves back and forth, sucking gas from the evaporator and pumping it into the condenser under high pressure.

The key element of this system are the valves. They are thin metal plates that act like petals. Their task is to pass gas in only one direction. There is a suction valve at the inlet to the cylinder, and a discharge valve at the outlet. As the piston moves downward, a vacuum is created and the suction valve opens, admitting gas. When moving upward, the gas is compressed, the suction valve closes, and the discharge valve opens, releasing the compressed gas into the system.

• 🔩 Piston: made of light alloys or steel, has minimal clearance with the cylinder walls.
• 🛑 Valve plates: the thinnest steel elements subject to wear and deformation during water hammer.
• ⚙️ Connecting rod: transmits force from the engine shaft to the piston, experiencing high tensile loads.

Valve wear is one of the most common causes of loss of compressor performance. If the plate breaks or is deformed, the compressor continues to hum, but stops pumping freon, and the cold in the chamber disappears.

Refrigerant and oil: working fluids of the system

There is always a certain amount inside the compressor refrigeration oil. It is necessary to lubricate rubbing pairs, seal the gaps between the piston and cylinder, and also to remove heat from heating parts. Unlike automobile oils, refrigeration oils have unique chemical resistance and the ability to mix with refrigerant without losing their properties.

The second important component is the refrigerant itself (freon). In modern refrigerators, R134a or R600a (isobutane)are most often used. Inside the compressor, freon is in a gaseous state, but under pressure it easily passes into the liquid phase. It is important to understand that the amount of freon is strictly regulated by the manufacturer.

The table below shows the main differences between the types of refrigerants used in household refrigerators:

Engine starting and protection system

For the operation of the compressor electric motor, a starting system is required. Since the engine must overcome resting inertia and system pressure, it requires an additional push. Responsible for this is starting relay, which briefly connects the starting winding. As soon as the rotor picks up speed, the relay turns off this winding.

The second important element is the thermal protection relay. It monitors the temperature of the compressor housing and the current strength. If the compressor overheats or the current exceeds the norm (for example, when jammed), the relay opens the circuit and stops the motor, preventing the windings from burning out. These elements are often located outside on the casing, but their operation directly affects the processes inside.

In inverter models, the role of the starting relay is performed by an electronic control unit that smoothly changes the frequency of the current, allowing the engine to start without jerking and operate in a wide range of speeds.

Typical problems and their impact on the contents

Over time, internal components wear out. The most common problem is burnout of the motor windings. This occurs due to power surges or lack of cooling. In this case, soot and acidis formed inside the housing, which contaminates the oil and spreads throughout the entire tube system, requiring thorough washing.

Another common problem is wear of the mechanical part. The appearance of play in the bearings or a gap between the piston and cylinder leads to a drop in pressure. The compressor is running but does not create the required pressure drop for effective cooling. In such cases, a metallic clanging or clanging sound is often heard.

⚠️ Attention: If you hear a loud metallic clanging or knocking sound inside the compressor, this is a sign of damage to the engine mount or valve train. Operation in this mode will lead to complete jamming of the shaft within several hours or days.

Moisture may also enter the system. Water reacts with oil and freon to form an acid that corrodes the copper tubes and motor windings from the inside. This process is irreversible and requires replacement of the compressor and filter-drier.

Is it possible to repair a compressor?

The issue of repairing the “internals” of a compressor often causes controversy. Theoretically, you can cut the housing, replace the piston group or rewind the engine, and then weld the casing back. However, in practice such repair not economically feasible. The cost of work and new parts often exceeds the price of a new compressor, and there is practically no guarantee for such repairs.

In addition, in the factory, an ideal vacuum is created and filled with gas, which is extremely difficult to replicate in a garage environment. Violation of the assembly technology will lead to rapid failure of the repaired unit. Therefore, craftsmen prefer to completely replace the unit.

The only thing that can be serviced are the external elements: relays, capacitors and a cooling fan (if there is one). The internal part is considered a non-repairable unit.