When the refrigerator stops cooling or makes strange sounds, the first suspicious object becomes its “heart” - the compressor. Many users mistakenly call it just a motor, without thinking about the complex processes hidden inside the sealed metal case. Understanding what exactly is hidden in this black tank helps to better diagnose breakdowns and explains why self-repair of this unit is almost impossible without special equipment.
The inner world of a compressor is high-precision mechanics operating under extreme conditions of pressure and temperature. There is no room for random details: each element performs its function of compressing the refrigerant and ensuring its circulation throughout the system. Let's look at what this unit consists of and how its components interact to maintain cold in your chamber.
It is important to immediately note that modern household refrigerators are equipped primarily with piston or linear hermetic compressors. This means that the housing is completely sealed in production. Inside there is not only the engine itself, but also the compression mechanism, as well as the oil necessary to lubricate the rubbing parts. Access to the insides without destroying the casing is impossible, which makes this unit unrepairable in domestic conditions.
⚠️ Attention: It is strictly forbidden to open the compressor housing for inspection. There may be residual pressure inside, and refrigerant and oil vapors, when in contact with air and an open flame (during soldering), form toxic compounds.Sealed casing and its contents
Externally, the compressor is a black metal cylinder or sphere, often called "potty". This casing performs a double function: it serves as a reservoir for the refrigerant during suction and at the same time serves as a muffler that reduces the noise of the mechanism. Inside this space there is a vacuum when the system is working correctly.
The bulk of the internal volume is occupied electric motor by the compressor part. They are located vertically and mounted on a spring suspension. This design (“internal suspension”) makes it possible to dampen vibrations that inevitably arise during piston operation. If the springs burst, you hear a characteristic metallic clanging and knocking sound when starting.
- 🔩 Lower part: here is an electric motor immersed in oil.
- ⚙️ Upper part: there is a cylinder-piston group where the gas compression.
- 🌡️ Middle zone: space filled with freon vapor, which cools the engine windings.
The casing has three process outlets (tubes): two copper for connection to the cooling system (suction and discharge) and one sealed for charging with refrigerant and oil. It is through these tubes that the internal contents of the motor interact with the rest of the refrigerator circuit.
Electrical part: stator and rotor
The foundation of the entire unit is the electric motor. Most household models use squirrel-cage asynchronous motors. They are reliable and simple, but require precise balance during manufacture. The engine consists of two main elements: a stationary stator and a rotating rotor.
Stator is a set of metal plates in the grooves of which windings of copper wire are laid. Usually there are two of them: starting and working. The start winding is turned on for a short time to create the initial torque, after which it is turned off by the start relay. The working winding ensures constant rotation.
⚠️ Attention: When the windings burn, the oil inside the compressor becomes acidic. Installing a new motor without flushing the refrigerator system will lead to repeated failure in a few months.Inside the stator there is rotor a shaft with a set of plates and short-circuited turns. It has no electrical contact with the outside world. The current flowing through the stator windings creates a magnetic field that drags the rotor along with it. The rotor shaft is elongated and rises upward, where a crank is eccentrically fixed at its end, driving the piston.
Why does the winding burn out?
Most often this happens due to voltage surges, jamming of the mechanical part or a malfunction of the starting relay, which does not turns off the starting winding.
Compression mechanism: cylinder and piston
The compressor part is located above the electric motor. This is the heart of the pump, where the physical compression of freon gas occurs. The design here is simplified as much as possible to ensure reliability. The main element is a cylinder, inside which a piston moves back and forth.
The piston is driven by a crank mechanism. As the engine shaft rotates, the crank forces the piston to move up and down. Unlike automobile engines, there are no rings on the piston in the classical sense - the gap between the piston and the cylinder wall is minimal, and tightness is ensured by precision processing and oil viscosity.
- 📉 Suction stroke: the piston moves down, creating a vacuum, and gas enters through the suction valve.
- 📈 Discharge stroke: the piston moves upward, compressing the gas to high pressure.
- 🚪 Valve group: thin metal plates, working like valves, open and close under the influence of gas pressure.
At the end cylinder installed valve plate. It is pressed against the cylinder head. It is this unit that most often fails due to water hammer (liquid freon entering the cylinder) or during prolonged operation without load. Deformation of the valve plates leads to a drop in compressor performance.
📊 What compressor problem have you encountered most often?It hums but does not startIt burns and knocks out the lightIt works but does not coolA knock is heard insideLubricating system and oil
The lower third of the internal volume of the casing is filled with special compressor oil. It performs a critical function: it lubricates rubbing pairs (motor shaft, bearings, cylinder) and removes heat. The oil level is strictly regulated by the manufacturer.
The most important element of the lubrication system is oil pump (oil lifter). It is often designed as a spiral channel inside the rotor shaft. When the shaft rotates, the oil, under the action of centrifugal forces and vacuum, rises upward through the channel, to the bearings and cylinder-piston group. After lubrication, the oil flows back into the crankcase.
Using the wrong type of oil can lead to disastrous consequences. Modern refrigerators use synthetic oils (POE, PVE), which are hygroscopic (absorb moisture) and chemically active. Moisture getting into the system when changing the oil requires deep vacuuming.
Parameter Mineral oil Synthetic oil (POE/PVE) Compatibility Freons R12, R134a Freons R600a, R134a, R404a Hygroscopicity Low High (requires protection from air) Viscosity Stable Changes over time Price Low High ⚠️ Attention: Mixing oils of different types and manufacturers is prohibited. The chemical reaction can lead to precipitation, which will clog the capillary tube of the refrigerator.Start protection relay and thermal protection
Although the start relay is technically located externally on the motor housing, it is an integral part of the electrical circuit that controls what is inside. Without this device, starting a squirrel-cage engine would be impossible or would lead to its combustion.
The relay consists of two main components: an electromagnetic starting relay and a bimetallic thermal protection. At the moment of switching on, current passes through the working winding and the coil of the starting relay. The magnetic field draws in the core, closing the contacts of the starting winding. The engine begins to accelerate.
When the speed reaches 75% of the rated speed, the current in the circuit drops, the starting relay core falls under the influence of gravity (or a spring), opening the starting winding circuit. If the motor is overloaded or jammed, the current increases, the bimetallic plate heats up and opens the circuit, protecting stator windings from overheating.
☑️ Diagnostics of the compressor relay
Completed: 0 / 4Linear compressors: difference from the classics
In recent years, linear inverter compressors have become increasingly common in premium refrigerators (for example, LG, Samsung, Bosch). They fundamentally change the design of what is inside the motor. There is no rotating rotor or crank mechanism.
The piston movement is carried out by a linear electromagnetic drive. A piston with magnets moves back and forth inside the coil. The frequency of movement is regulated by an inverter, which allows you to smoothly change the cooling power, and not just turn the motor on and off, as in classic models.
This design contains fewer rubbing parts, which theoretically increases the service life. However electronic filling such compressors are much more complex. Inside the casing there are also piston position sensors that transmit data to an inverter board located outside (or integrated in some models).
Linear motors are quieter and more economical, but their diagnostics require special equipment. Using a regular tester to check the serviceability of the windings of a linear compressor is often not enough, since it is necessary to evaluate the resistance and insulation in dynamics.
Diagnostics and typical faults
Understanding the device helps determine the nature of the breakdown. If the refrigerator hums, but does not start, and after a few seconds a click is heard, most likely the problem is in the start relay or a jammed mechanical part (piston). If the motor hums quietly and the housing is cold, the winding may break.
When there is an interturn short circuit in the stator windings, the motor consumes increased current, gets very hot and quickly knocks out the thermal protection. In this case, local overheating of the varnish on the wire occurs inside the motor, which leads to further destruction of the insulation.
If you hear a metallic knock inside the running motor, this is a sure sign that the suspension spring has burst or the shaft bearing has collapsed. Operation of such a unit is impossible, since vibration will quickly destroy the tubes and lead to freon leakage.
Is it possible to change the oil in the compressor yourself?
Theoretically, yes, if you carefully cut off the casing, but in practice this is impractical. You will need to weld the body back together under an inert gas environment to avoid oil oxidation and acid formation. It is easier and cheaper to buy a new compressor.
Why is the compressor hot to the touch?
During normal operation, the compressor housing heats up to 70-90 degrees Celsius. This is due to the fact that freon vapor passing through the casing takes away heat from the motor windings. If the temperature exceeds 100-110 degrees, this is a sign of overload or problems with the cooling system.
What does “pop” mean when you turn on the refrigerator?
A loud pop or click at start often indicates a breakdown of the starting capacitor (if it is in the circuit) or a water hammer if liquid has entered the system. Also, such a sound can be made by a rubbing winding during a short circuit.
How long does a modern compressor last?
The average service life of a piston compressor is 10-15 years. Manufacturers often claim that linear inverter models have a service life of up to 20 years, but the actual figure greatly depends on the stability of the network voltage and operating conditions (room temperature, frequency of door openings).