The compressor is rightly called the “heart” of any refrigeration system, and it is on its proper operation that it depends whether your refrigerator will be cold or the food will begin to spoil. Many owners of household appliances do not even think about what is hidden under the black metal “belly” on the back wall of the unit until they are faced with a breakdown or noisy operation of the device. Understanding what the compressor is made of what is the compressor made of?, helps not only to correctly diagnose faults, but also to consciously approach the selection of new equipment or spare parts for repair.
The design of this unit is a complex engineering symbiosis of electrical engineering, mechanics and chemistry, where each element performs a critical function. Inside the sealed casing there are electric motors, piston groups, valves and a lubrication system operating in an aggressive environment under high pressure. We will analyze in detail the materials used in the production of various types of compressors so that you can better navigate the technical documentation.
Knowledge of the internal structure is also necessary to understand the causes of characteristic noise, vibration or overheating of the unit. If you are planning self-diagnosis or simply want to expand your technical horizons, this information will become the foundation for further actions. Let's figure out what metals, alloys and insulating materials are used by engineers to create a reliable refrigeration heart.
Main body: tightness and strength
The outer shell of the compressor, which you see on the back panel of the refrigerator, is made of durable sheet steel. This element is called a sealed casing, and its main task is to hold the refrigerant under high pressure and protect the internal mechanisms from dust, moisture and mechanical damage. The steel for the housing is selected taking into account corrosion resistance, since the unit often operates in conditions of high humidity in the kitchen.
The two halves of the housing are connected to each other by welding, which ensures complete tightness of the system for the entire service life. Sealed casing also acts as a resonator, dampening some of the noise from the running engine, although such a design cannot completely eliminate sound vibrations. Inside the casing, a pressure is created that is close to atmospheric or slightly higher than it, which depends on the type of refrigerant and the stage of the cycle.
On the surface of the casing there are three main pipes: two copper for connection to the refrigeration system circuit (suction and discharge) and one sealed process fitting for filling freon. The quality of the welds and the thickness of the metal directly affect the durability of the device, since depressurization of the housing usually means replacing the entire assembly.
⚠️ Attention: It is strictly forbidden to open the welded compressor housing at home without special equipment for evacuation and filling, as this will lead to irreversible damage to the system.
Electrical part: the heart of the engine
Inside the steel casing there is an electric motor that drives the piston group or rotor. The basis of the engine is stator, assembled from thin plates of electrical steel. The use of plates, rather than a monolithic piece of metal, allows us to minimize energy losses due to eddy currents, which inevitably arise when working with an alternating magnetic field.
The stator winding is made of copper wire coated with several layers of varnish insulation. Copper was chosen for its high electrical conductivity, which reduces engine heating during long-term operation. The temperature resistance of the winding varnish must withstand heating up to 150-180°C, otherwise an interturn short circuit will occur and motor combustion. Cheaper models sometimes use aluminum, but its use reduces the efficiency and reliability of the unit.
The motor rotor, rotating inside the stator, is also assembled from steel plates and can be made in the form of a short-circuited cage. The rotor shaft extends beyond the plate pack and is connected to the crank mechanism. To ensure smooth running and reduce friction, the shaft rests on sliding or rolling bearings, which are constantly washed with oil.
The electrical part also includes a start-up relay, which is mounted externally on the casing or inside it. This small block is responsible for supplying an impulse to the starting winding and protecting the motor from overcurrent. Without the correct operation of the relay, the engine will not be able to overcome the inertia of rest and start.
Mechanical part: pistons and valves
The mechanical group converts the rotational movement of the engine shaft into the translational movement of a piston, which compresses the gaseous refrigerant. The main element here is crank mechanismconsisting of a crankshaft, connecting rod and piston. These parts experience enormous loads and must be made of high-strength materials.
The piston is usually made of a special aluminum alloy or cast iron, which has a low coefficient of friction and high wear resistance. A special graphite or Teflon coating is often applied to the piston surface to improve sliding. The connecting rod connects the piston to the crankshaft and transmits the force necessary to compress the gas.
A critically important mechanical element is the valve group located at the end of the cylinder. It consists of the thinnest steel plate valves (petals), which open and close under the influence of gas pressure. Suction valve passes gas into the cylinder, and the discharge valve releases compressed gas into the system. The petals must be extremely flexible and durable to withstand millions of opening and closing cycles without breaking.
☑️ Signs of wear on the mechanical part
In inverter and linear compressors, the design may be different: there the piston can move linearly under the influence of an electromagnetic field, which eliminates the need in the crank mechanism and reduces the number of rubbing parts.
Lubricating system and refrigerants
For normal operation of the rubbing parts inside the compressor, oil is needed. Unlike automobile engines, a special compressor lubricant is used here, which must be chemically compatible with the refrigerant and seal material. The oil is located in the lower part of the casing, and when the engine is running, it is sprayed or supplied under pressure to the bearings and cylinder.
The choice of oil type depends on the freon used. For older refrigerants such as R12, mineral oils were used. Modern environmentally friendly refrigerants (R134a, R600a, R404A) require the use of synthetic oils, such as polyesters (POE) or polyvinyl ethers (PVE). These oils are highly hygroscopic, that is, they actively absorb moisture from the air, which is their weak point.
The table below shows the correspondence of the types of oils and refrigerants used in modern refrigerators:
| Refrigerant type | Oil type | Compatibility features |
|---|---|---|
| R12 (Freon-12) | Mineral | Not hygroscopic, incompatible with modern synthetics |
| R134a | Polyester (POE) | High hygroscopicity, requires vacuuming |
| R600a (Isobutane) | Mineral / Alkylbenzene | Explosive, small amount of oil in the system |
| R404A / R507 | Polyester (POE) | Used in industrial refrigeration and freezers |
If moisture gets into a system designed for synthetic oil, a chemical reaction may occur with the formation of acids, which corrode motor windings and metal parts. Therefore, during repairs, it is important to maintain tightness and use only original refrigerants.
Vibration insulation and acoustic comfort
A running compressor creates vibrations that are transmitted to the refrigerator body and can cause loud noise. To minimize this effect, engineers use various vibration isolation systems. The compressor itself is attached to the frame of the refrigerator through special damper springs or rubber-metal supports.
Additional noise damping elements can also be located inside the casing. For example, the suction pipe is often made in the form of a long curved tube or equipped with a muffler so that pulsating gas flow does not create sound waves. Expensive models use internal engine suspension on springs directly inside the welded housing.
The quality of assembly and balancing of rotating parts directly affects the noise level. If the refrigerator begins to hum more than usual, this may indicate that the internal dampers are damaged or the fastenings are loose. In some cases, replacing the rubber washers under the bolts securing the compressor to the frame helps.
Why is a new refrigerator humming?
New compressors may be louder than older ones due to higher rotation speeds and the use of environmentally friendly, but less efficient refrigerants that require higher pressure.
Differences in materials inverter models
With the development of technology, classic piston compressors are being replaced by inverter and linear models. They have changed not only the control electronics, but also the design of the mechanical part. For example, in LG linear compressors, the piston is driven by a linear electric motor, where the coil and magnets are arranged linearly rather than in a circle.
This design eliminates many rubbing parts, such as connecting rods and the crankshaft. This reduces wear points and reduces noise levels. The materials used here are the same - steel, copper, special alloys, but the geometry of the parts itself is different. Inverter compressors often have more compact dimensions with the same power.
The electronic control board, which is an integral part of the inverter compressor, contains powerful transistors and capacitors. These elements are sensitive to power surges in the network, so the quality of the board's element base directly affects the reliability of the entire node. Unlike conventional models, where the relay clicks every time it starts, the inverter operates smoothly, regulating the speed of rotation of the shaft.
⚠️ Attention: When replacing a conventional compressor with an inverter one (and vice versa), a complete rework of the electrical circuit of the refrigerator is necessary, since they are not interchangeable without modifications.
Frequently asked questions about the design of the compressor
Is it possible to replace the copper winding with aluminum during repairs?
Theoretically, it is possible to rewind the motor, but in practice this is impractical. Aluminum wire has lower conductivity, so to obtain the same power you will have to increase the cross-section or number of turns, which will change the magnetic properties of the motor. In addition, factory insulation and varnish impregnation technology cannot be reproduced at home, which will lead to rapid combustion of the repaired unit.
Why is there oil inside the compressor if it is sealed?
Oil is necessary to lubricate the rubbing pairs: the piston and cylinder, shaft bearings. In hermetic compressors, the oil circulates along with the refrigerant through the system, but most of it is located in the crankcase (the lower part of the casing). A special design allows the oil to return back to the compressor so that oil starvation does not occur.
What is the piston made of and can it burst?
Pistons are made of aluminum alloys or cast iron. They can burst extremely rarely, usually due to water hammer (liquid freon entering the cylinder) or when the engine jams. More often, wear of the piston rings or breakage of the valve plates occurs, which leads to a drop in pressure.
What is the difference between the steel of the housing and the steel of the stator plates?
The housing is made of ordinary structural steel, the main requirement for which is strength and weldability. The stator plates are made of electrical steel with the addition of silicon, which significantly reduces energy losses due to magnetization reversal and heating. You cannot use ordinary steel for the engine core - it will quickly overheat.