What a refrigerator compressor looks like from the inside

It is impossible to look inside a working compressor without opening it, since this unit is a sealed steel cylinder, which is welded at the factory forever. However, understanding what's hidden under that black "can" is critical for any repairman or tech-savvy appliance owner. It is here that the refrigerant is compressed, due to which heat is transferred from the inner chamber to the outside.

Visually from the outside we see only the housing, the start relay and copper tubes, but inside hides a complex mechanism operating under high pressure. Sealed casing protects electrical components and moving parts from moisture and dust, but at the same time hides the main components from our view. If we could take an X-ray or carefully cut the body, an amazing picture of engineering would appear before us.

The main task of this unit is to create a pressure difference in the system, forcing freon to circulate and change its state of aggregation. There is an aggressive environment inside: a mixture of oil and refrigerant, high temperatures and constant vibration. This is why the quality of the workmanship and the balancing of the parts inside are critical to the longevity of the entire refrigerator.

Sealed casing design and suspension

The outer casing, or casing, is made of stamped steel. It is divided into two hemispheres, which are connected by a weld along the equator. Inside this space there is a pressure close to atmospheric or slightly elevated, depending on the temperature and type of refrigerant. The entire working mechanism is not rigidly attached to the walls, but is suspended on special springs.

This suspension system is an ingenious solution by engineers to compensate for the vibrations of a running motor. If the engine were rigidly mounted, the noise during operation would be unbearable, and the vibrations would destroy the soldering of the tubes. Springs dampen vibrations, but at the same time they must be tensioned in order to support the weight of the unit.

There are two types of suspension: internal and external. Most household models use internal suspension, where the springs are located directly inside the casing. This makes replacing springs or repairing them an extremely difficult task, requiring complete disassembly of the housing and subsequent re-sealing.

⚠️ Attention! Opening the sealed compressor casing at home without special equipment for vacuuming and sealing leads to irreversible damage to the unit. An attempt to simply “look” inside will end with moisture and air getting into the system.

Three copper fittings are welded to the top of the casing: two for connecting to the refrigerator circuit (suction and discharge) and one technological, which is used when refueling and is subsequently sealed. Electrical contacts pass through the bottom, sealed with glass or special ceramics, so that current flows to the windings, but air does not penetrate inside.

Electrical part: stator and rotor

In the lower part of the casing there is an electric motor that drives the piston group. This is an asynchronous AC motor, consisting of a stationary stator and a rotating rotor. Stator is a package of assembled electrical steel plates with copper windings laid in grooves.

The windings are divided into starting and working. The working winding creates the main magnetic field, and the starting winding helps the rotor overcome the inertia of rest and begin to rotate. To control this process, a starting relay is used, which is located outside, but is electrically connected to the internal windings through contacts passing through the bottom of the casing.

The rotor is pressed onto the shaft, which is the central axis of the entire mechanism. It is made of special electrical steel and has the shape of a cylinder with slots. When voltage is applied, a rotating magnetic field appears in the stator windings, which drags the rotor along with it. The rotor shaft is eccentrically connected to the piston connecting rod.

It is important to note that the motor windings are constantly washed with refrigerant vapor and oil. This provides excellent cooling of the electrical part, but requires the oil to have certain dielectric properties. In modern inverter models, the operating principle may differ, but the classic scheme remains the most common.

Crank mechanism and piston group

The heart of the compressor is the crank mechanism, which converts the rotational movement of the shaft into the translational movement of the piston. The engine shaft has a special bend - a crank, onto which a connecting rod is placed. When the shaft rotates, the connecting rod makes oscillatory movements up and down.

At the upper end of the connecting rod is fixed pistonwhich moves inside the cylinder. In older models, pistons were made of cast iron, in modern ones - from light alloys or even special plastic with graphite filling to reduce friction. The gap between the piston and the cylinder walls is minimal, but necessary for free movement.

The cylinder can be part of the compressor block itself or a separate bushing. It is in the cavity of the cylinder that the compression of gaseous freon occurs. The piston movement is strictly vertical (in linear compressors) or with a slight inclination, depending on the design of the unit.

Lubrication of rubbing pairs - connecting rod, shaft and piston - occurs by splashing. At the lower end of the shaft there is often a screw thread or blade, which, when rotated, captures oil from the crankcase and lifts it up the shaft, providing lubrication to the bearings and cylinder-piston group.

Valve system and flow distribution

One ​​of the most important and delicate (sensitive) parts of the internal structure is the valve group. It is located at the end of the cylinder and is responsible for the direction of movement of the refrigerant. Gas must flow in only one direction: from the evaporator to the cylinder, and from the cylinder to the condenser.

The system consists of suction and discharge valves. These are the thinnest metal plates that work as check valves. As the piston moves downward, a vacuum is created and the suction valve opens, admitting gas. As the piston moves upward, the pressure increases, the suction valve closes, and the discharge valve opens, releasing compressed gas.

Thinness of the valve plate plays a critical role. If it is too hard, there will be knocking and loss of efficiency. If it is too soft, it will quickly break or will not fit tightly. Often valves are made in the form of tongues, fixed at one end.

Above the valve group there is a plate with noise suppressors. The compressed gas comes out under high pressure with a characteristic whistle, and the system of internal chambers and channels in the block cover smoothes out these pulsations, reducing acoustic noise.

Oil system and lubrication of components

There is always a certain amount of compressor oil inside the compressor. It does not circulate through the cooling system in large volumes (although a small amount always moves with freon), but is located in the lower part of the casing - in the crankcase. The oil level is strictly standardized by the manufacturer.

The main function of the oil is to lubricate rubbing parts and remove heat from them. In addition, the oil creates additional sealing of the gaps between the piston and the cylinder. Oil viscosity must match the type of refrigerant used. For freons R134a and R600a (isobutane), different types of oils are used, which are not always compatible with each other.

Oil is supplied to the rubbing pairs under pressure created by the rotation of the shaft itself. The shaft design often includes spiral grooves that act like an auger, drawing oil from the bottom to the top. In the upper part of the shaft, oil sprays, irrigating the internal walls and the piston.

If there is not enough oil, dry friction occurs, rapid heating and jamming of the mechanism. If there is too much oil, a water hammer effect occurs when liquid oil enters the cylinder and the valves do not have time to pass it, which leads to their breakdown.

Types of internal structures: linear and inverter

The classic compressor described above operates on the principle of reciprocating motion. However, other mechanisms may be hidden inside the casing. For example, in inverter models the principle of operation of the engine has been changed: it can change the rotation speed, which allows you to smoothly adjust the power without frequent switching on and off.

Linear compressors, popular in LG technology, stand out. Inside such a unit there is no rotating shaft and connecting rod in the classical sense. The piston is driven by a linear electromagnetic motor. The magnetic field pushes the piston forward and backward in a straight line.

This design has fewer rubbing parts, which theoretically reduces noise and vibration. However, inside a linear compressor there are also springs, a piston and valves that operate in a harsh environment. Diagnostics of such models is more difficult due to the lack of a classical starting circuit.

Despite the differences in the drive, the principle of gas compression by a valve group remains the same for all household refrigerators. The gas is sucked in, compressed by reducing the volume of the chamber and pushed into the system.

Diagnostics of faults by indirect signs

Although we do not see the insides, the condition of the components can be judged by external signs. A loud knocking noise when starting up often indicates a problem with the suspension or valves. If the compressor hums but does not start, there may be a wedge in the mechanical part or a break in the windings.

The absence of vibration on the body of a running compressor is an alarming sign. This may mean that the shaft is turning idle (the connecting rod is cut off or the bearing is turned), and gas compression does not occur. The refrigerator will stop freezing, although the motor will work.

The heating of the body is also informative. An excessively hot compressor may indicate overload operation, valve failure (gas is rushing back and forth, heating up from compression) or oil problems. Casing temperature above 90 degrees Celsius considered critical for most household models.

To accurately diagnose the internal condition, an autopsy is required, but this will no longer be a diagnosis, but the beginning of a major overhaul or disposal, since it is almost impossible to restore factory tightness and balancing in a garage.