Many owners of household appliances perceive the refrigerator as a “black box”: you plug the plug into the socket, it becomes cold inside, and the food does not spoil. However, when this “box” stops humming or, conversely, begins to make noise so much that it can be heard throughout the entire apartment, a natural interest arises in what makes the system work. The heart of any unit is the compressor, and it is its internal structure that determines the efficiency and durability of the entire cooling system.
It is impossible to look inside this unit without breaking the seal, since it is a sealed steel casing. However, understanding what processes occur in a cavity hidden from view helps to correctly diagnose faults and avoid fatal errors during operation. In this article, we will look at the anatomy of the motor, the types of mechanisms used, and the physical and chemical reactions that provide coldness in your kitchen.
Inside the housing hides a complex system for converting electrical energy into mechanical movement that compresses the refrigerant gas. It is this process, occurring in a closed loop, that allows heat to be removed from the refrigerator chambers to the outside. A detailed study of the components helps to understand why some models operate silently, while others emit vibrations, and what chemical processes ensure the circulation of freon.
Design and types of compressor units
Before considering the insides, it is necessary to understand what type of device we are dealing with. Modern household refrigerators dominate piston compressorsalthough inverter models are increasingly found in the premium segment. Externally, they look like massive black “barrels” welded to the rear wall, but inside their design can differ significantly in the principle of operation and arrangement of elements.
The classic piston mechanism works on the principle of an internal combustion engine, only instead of fuel it uses electricity, and instead of exhaust gases - compressed refrigerant. Inside the sealed housing there is an electric motor that rotates the crankshaft. A piston is attached to this shaft, making reciprocating movements inside the cylinder, creating the necessary pressure for the circulation of freon.
Inverter models are more complex: they do not have a rigid connection between starting and stopping the motor. Inverter compressor is able to smoothly change the speed of rotation of the shaft, which reduces energy consumption and noise levels. Inside such a device, more advanced bearings and a lubrication system are often used, designed for continuous operation without sudden load surges characteristic of conventional start-stop systems.
Electric motor and starting system
The basis of the internal space is occupied by the electric motor, which makes up more than 60% of the body volume. This is an asynchronous motor with a squirrel-cage rotor, operating from a single-phase network. To start rotor rotation, a phase shift is required, for which the starting and working stator windings are responsible. It is these copper windingswound on the core that create a magnetic field that sets the rotor in motion.
The most important element of the starting system is the starting relay. It is located outside or inside the casing (depending on the model) and is responsible for short-term connection of the starting winding. As soon as the rotor reaches the required speed, the relay opens the circuit and the engine continues to operate only on the working winding. Older models used posistors, while new ones used electromagnetic relays, providing more precise control.
Inside the casing there are also wires connecting the windings to the external terminal box. These connections must be absolutely reliable, since any spark inside a closed volume filled with oil and freon vapors could theoretically be dangerous, although modern refrigerants and oils have dielectric properties. The reliability of the insulation here is critical to prevent short circuits.
Why does the starting winding burn out?
A common cause of failure is a stuck starting relay or low voltage in the network. If the relay does not open the circuit in time, the starting winding, designed for short-term operation, overheats and burns out, which leads to a complete stop of the compressor.
Crank mechanism and piston group
The mechanical part, hidden inside the steel casing, is a classic crank mechanism. The crankshaft, rotated by an electric motor, transmits force to the piston through a connecting rod. The piston moves inside the cylinder, alternately creating zones of rarefaction and high pressure. The accuracy of processing of these parts determines Compressor efficiency and its ability to create the required pressure in the system.
Special compression rings are installed on the piston, which ensure the tightness of the gap between the piston and the cylinder walls. These rings prevent gas from flowing from a high pressure area to a low pressure area. Wear of the rings is one of the common causes of loss of performance: the engine hums, but does not produce cold, since it cannot create sufficient pressure for freon condensation.
The suction and discharge valves are located in the upper part of the cylinder. These are thin plates made of special steel that work like automatic shutters. They open and close under the influence of pressure differences, allowing gas to flow in only one direction. Violation of the tightness of these valves valves (cracks, deformation) leads to the fact that the gas begins to circulate back and the refrigerator stops freezing.
Lubricating system and the role of oil
In the lower part of the compressor housing, at the bottom, there is a special compressor oil. It is necessary to lubricate rubbing parts: crankshaft bearings, cylinder walls and piston. Since the system is sealed, the oil does not require changing during its entire service life unless a refrigerant leak or serious failure occurs. The oil level is strictly regulated by the manufacturer.
Lubrication is carried out by splashing. At the bottom end of the crankshaft there is often a helical groove or scoop, which, when rotated, captures oil and lifts it up the shaft. From there it is sprayed onto the bearings and cylinder walls. After lubrication, the oil flows back to the bottom, forming an oil mist, which is partially carried away by the refrigerant flow into the system, but is then separated in the condenser and returned back.
It is important to understand that the oil in the refrigerator performs not only a lubricating, but also a sealing function, filling microscopic gaps. Different models use different types of oils: mineral (for freons R12, R22) or synthetic polyester (for environmentally friendly R600a, R134a). Mixing different types of oils is strictly prohibited, as this can lead to the formation of acids and blockage of the system.
| Refrigerant type | Type of compatible oil | Features | Application |
|---|---|---|---|
| R12 (Freon-12) | Mineral | High viscosity, hygroscopic | Old Soviet refrigerators |
| R134a | Synthetic (POE) | Hygroscopic, requires vacuuming | Modern models until the 2010s |
| R600a (Isobutane) | Synthetic (POE/AB) | Explosive if leaked, small volume | Most modern refrigerators |
| R290 (Propane) | Synthetic | High efficiency, flammability | Industrial and new household models |
Refrigerant: condition and circulation
Although the main volume of refrigerant is in the condenser and evaporator tubes, inside the compressor it is present in a gaseous state. At the moment of suction, low temperature and pressure are drawn into the body through the pipe. Passing through the internal cavity of the motor, the gas cools the windings of the electric motor, preventing them from overheating, before entering the cylinder for compression. gas freon low temperature and pressure. Passing through the internal cavity of the motor, the gas cools the windings of the electric motor, preventing them from overheating, before entering the cylinder for compression.
The compression process in the cylinder turns the gas into high pressure and high temperature steam. It is in this state that it exits through the discharge pipe and is sent to the condenser (radiator on the rear wall), where it cools and turns into a liquid state. The cycle is repeated continuously until the thermostat gives the command to stop.
Modern environmentally friendly models use isobutane (R600a). Its amount in the system is very small (about 30-50 grams), and the operating pressure is lower than that of old freons. This allows compressors to be made more compact and quieter. However, if you are planning on diagnosing yourself, remember: R600a is heavier than air and, if leaked, accumulates below, creating an explosive mixture.
⚠️ Attention: Internal pressure in the system can remain even when the refrigerator is turned off. Never attempt to cut through copper pipes or open the compressor casing without first removing the refrigerant with professional equipment. This can lead to injury and the release of harmful substances.
Causes of breakdowns and diagnosis of internal defects
Understanding the internal structure helps to more accurately determine the cause of the breakdown. If the compressor hums but does not start, the problem may be a jammed piston group or a faulty start relay. If the engine runs but does not cool, valve wear or loss of compression due to worn piston rings is likely.
A frequent problem is “water hammer.” This happens when it is not gas that enters the cylinder, but liquid freon or oil. The liquid does not compress, and the piston, resting against it, can break the connecting rod or valves. This usually happens when the thermostatic valve malfunctions or when the system is not properly charged after repair.
It is also worth mentioning the interturn short circuit of the windings. When the insulation breaks down, the motor begins to consume huge current, hum and quickly heat up. In this case, the thermal protection relay is activated, opening the circuit. After cooling, the relay closes the circuit again, and the cycle repeats until the windings are completely burned out.
☑️ Diagnosis of a faulty compressor
⚠️ Attention: If you smell burning or see sparking in the area of the compressor terminal box, immediately unplug the refrigerator. Further operation may lead to a wiring fire or complete failure of the unit without the possibility of recovery.
Is it possible to repair the compressor yourself?
The issue of repairing the “internals” of the compressor often causes controversy. Theoretically, if you carefully cut off the top cover of the casing (“cap”), you can get to the mechanical part. However, factory resealing at home is not possible. Any microscopic gap will lead to the rapid release of freon and the entry of moisture into the system.
There is a method of “wedging” a stuck piston by applying increased voltage or hydraulic pressure, but this is a temporary measure. It is almost impossible to replace mechanically damaged parts (connecting rod, cylinder) inside a sealed housing without specialized equipment and inert gas welding skills.
Modern repair economics dictate its own rules: replacing the compressor assembly is often cheaper and more reliable than trying to overhaul the internal mechanism. The new unit is guaranteed to last for the stated period, while the restored “inner world” of the old motor can fail at any moment.
Thus, what is inside the refrigerator compressor is a mechanism that requires ideal operating conditions. Understanding its structure helps you be more careful with your equipment: do not tilt the refrigerator excessively during transportation (so that the oil does not go into the circuit), let it settle before turning it on, and monitor the cleanliness of the condenser so that the motor does not overheat.
Why is the compressor hot to the touch?
Gas is compressed inside the compressor, which, according to the laws of physics, is always accompanied by the release heat. In addition, the electric motor also heats up during operation. A case temperature of 50-70°C is normal. If the housing is heated to 90°C or higher, this may indicate an overload, a malfunction of the cooling fan, or problems with refrigerant circulation.
Is it possible to change the oil inside the compressor?
In a home workshop, no. This requires complete disassembly of the mechanism, washing of all parts with a special solvent, drying in an oven to remove moisture and assembly in a vacuum. Any remaining moisture or old oil will cause rapid failure. It is easier and cheaper to replace the entire compressor.
What does a knock inside a working compressor mean?
A knock usually indicates mechanical failure: a connecting rod has burst, a piston has broken, or the crankshaft bearings have failed. Sometimes the knocking noise can be caused by the vibration of pipelines against the body, which is less dangerous. But a dull metallic knock from inside the “barrel” is a sign of the need for urgent replacement of the unit.
Why are there springs inside the compressor?
In many models, the electric motor and mechanism are suspended on three internal springs. This is done to dampen vibrations that occur during piston operation. If the spring bursts or jumps off, the compressor begins to vibrate strongly and rumble loudly when starting and stopping, transmitting shocks to the refrigerator body.
Why can’t you turn the refrigerator on and off often?
If you turn it off abruptly, the pressure in the system does not have time to equalize. If you immediately turn on the compressor again, the piston will have to overcome high back pressure. This creates a huge load on the electric motor and mechanics, which can lead to jamming or burning of the windings. A time relay (protection) blocks the start for 3-5 minutes precisely to equalize the pressure.