A refrigerator is a complex unit, the heart of which beats in rhythm with the engine turning on and off. It is compressor responsible for the circulation of the refrigerant, creating the pressure necessary to cool the chambers. Many owners of household appliances do not even think about what this unit is made of until they are faced with a breakdown or the need for replacement.
The question of what metal the compressor housing is made of becomes critically important when trying to repair or dispose of it yourself. Not only the weight of the device depends on the material, but also its resistance to corrosion, ability to withstand high pressure and, importantly, the ability to carry out welding work. Understanding the structure of the metal helps to diagnose some types of malfunctions associated with freon leaks.
Modern industry uses time-tested technologies and alloys to produce these units. Hermetic compressors, which are found in 99% of household refrigerators, are a sealed “pot”, inside which there is an engine and a piston group. It is the outer shell and internal tubes that are of the greatest interest from the point of view of materials science.
Main body material: low-carbon steel
The vast majority of household compressors, be it Indesit, Atlant or Beko, have a body made of sheet steel. This is not a random choice of engineers, but the result of many years of testing. A special one is used, which has high ductility and strength. This material makes it possible to stamp two hemispheres, which are then welded along the equator, creating a sealed capsule. low-carbon steel, which has high ductility and strength. This material allows two hemispheres to be stamped, which are then welded at the equator, creating a sealed capsule.
Why steel? An excess pressure is created inside the compressor, which can reach several atmospheres depending on the type of refrigerant and the phase of the cycle. Aluminum or other light alloys might not be able to withstand such loads given the required wall thickness, or would require significant thickening, which would increase weight and dimensions. Steel provides an ideal balance between tensile strength and weight.
In addition, steel is an excellent heat conductor, which is important for cooling the windings of an electric motor immersed in oil. However, this material also has a downside: susceptibility to corrosion if the protective coating is damaged. If you see rust on the motor body, this is a signal that the paint layer is damaged, although a rusty “pot” itself does not mean a malfunction of the mechanism.
- 🔩 High mechanical strength protects internal components from damage.
- 🔩 Excellent weldability allows you to hermetically connect the two halves housing.
- 🔩 Good thermal conductivity helps remove heat from a running engine.
⚠️ Attention: Never try to drill into the housing of a compressor that is running or under pressure. Even the residual pressure of freon in combination with oil can lead to injury or fire.
Internal tubes and heat exchangers: copper or steel?
If the body is steel, then the question of what metal the tubes coming out of the compressor are made of requires more detailed consideration. Here the situation is ambiguous and depends on the year of manufacture and class of the refrigerator. In old models and premium technology, it was widely used copper. This metal has excellent thermal conductivity, ductility and, most importantly, is easily soldered with soft solders.
In modern budget and mid-budget models, manufacturers often switch to steel tubes (aluminized steel or stainless steel). This is done in order to save money, since copper is much more expensive. Steel tubes are silver in color, as opposed to the characteristic reddish-red hue of copper. They are stronger, but more difficult to install during repairs, as they require higher temperatures or special solders for connection.
There is also a bimetal option (bimetal), where the inner part of the tube can be made of one metal, and the outer part of another, or a copper-plated steel tube is used to facilitate soldering. You can determine the material visually or using a magnet: copper is not magnetic, steel is magnetic.
How to distinguish a copper tube from a steel one by eye?
Copper has a characteristic reddish-golden hue, which over time can oxidize to dark brown. Steel is always silver or gray. If the tube is covered with black enamel (as is often the case on the discharge line), the material can only be determined by a cut or a magnet.
The transition to steel tubes makes life more difficult for repairmen. If copper can be soldered with ordinary tin-lead solder, then steel often requires argon welding or the use of high-temperature containing solders, which requires more expensive equipment.
Piston group: cast iron, steel or aluminum?
Look inside the compressor without sawing it (which is disposable procedure) is impossible, but the technical documentation reveals the secrets of the internal filling. The piston group, which directly compresses the gas, is made of materials with a minimum coefficient of friction and high wear resistance. The traditional material for cylinders and pistons is cast iron or special steel alloys.
In some modern models, especially inverter ones, where the requirements for the weight of moving parts are higher, it can be used aluminum with special coating. However, pure aluminum is rarely used for friction pairs in a refrigerator compressor because of its softness and tendency to scuff during oil starvation.
The valves responsible for the direction of movement of freon are made of thin spring steel. This is a critical element: the valve must be flexible yet resilient to withstand millions of opening and closing cycles without loss of properties. Valve failure is one of the common causes of loss of compressor performance.
The influence of the type of refrigerant on the choice of materials
The materials used in the compressor directly depend on what refrigerant circulates in the system. Old refrigerators used R12 freon, which was aggressive to some types of rubber, but inert to metals. Modern gases, such as R134a or R600a (isobutane), dictate their conditions.
The type of refrigerant is especially important for compressors on R600a. Since isobutane is an explosive gas, the requirements for tightness and spark safety of the electric motor inside the housing have increased. The steel case in this case also acts as an additional safety barrier. The materials of the seals and engine windings are also selected taking into account chemical compatibility with oil and gas.
The pressure in systems with different freons is different. For example, R134a requires a higher condensing pressure than R12. This means that the compressor housing and connecting pipes must have a safety margin corresponding to the operating parameters of the gas. In this regard, steel is universal and reliable.
| Refrigerant type | Main material of tubes | System pressure | Material features |
|---|---|---|---|
| R12 (old) | Copper | Low | High corrosion resistance |
| R134a | Copper / Steel | Average | Requires synthetic oil |
| R600a | Steel / Copper | Low | Explosive, requires tightness |
Corrosion and protection of metal parts
Despite the use of high-quality steel, compressors are susceptible to corrosion. This happens not only due to moisture in the air, but also due to the aggressive environment in the kitchen, temperature changes and condensation. Factory painting of the compressor housing performs not only an aesthetic, but also a protective function.
You can often find black compressors. This is not just paint, but a heat-resistant coating that also promotes heat transfer. If you are planning to replace the compressor yourself, under no circumstances should you polish the metal on the outside until it shines unless it is required for soldering. Preserving the factory paint layer extends the life of the unit.
Particular attention should be paid to the place where the tubes exit the housing (fittings). This is where rusting most often begins, since the protective layer burns out during soldering. Craftsmen often treat these places with anti-corrosion compounds after completing repairs.
Comparison of steel and copper components during repair
For a repairman, the material of the compressor and tubes is a matter of labor intensity. Copper is forgiving: it is easy to bend, cut and solder. Steel requires more precise movements and proper selection of solder. When replacing a compressor, you often have to deal with a situation where the old tubes in the wall of the refrigerator are copper, and the new compressor comes with steel fittings.
In such cases, adapters or special solders are used to connect dissimilar metals (copper-steel). This connection is the critical point. If you use the wrong flux or solder, after a few months a microcrack may form at the joint and the freon will evaporate.
The weight of the compressor also depends on the metal. Steel units are heavier than their aluminum counterparts (if such were widely used in everyday life), which provides additional vibration resistance. A heavy compressor vibrates less on rubber feet, which reduces the overall noise of the refrigerator.
⚠️ Attention: When soldering steel tubes, be sure to use nitrogen purge or special fluxes that prevent the formation of an oxide film inside the tube. Oxides can clog the capillary tube and damage the new compressor.
Checklist: Identifying the material before repair
Before you begin replacement or repair, you need to accurately identify the materials with which you have to work. This will allow you to prepare the correct tools and consumables.
☑️ Checking the compressor materials
If you find that your refrigerator is equipped with steel tubes, and you have no experience in soldering steel, it is better to entrust this work to a professional or carefully practice on scraps. Steel requires a higher burner flame temperature and faster work to avoid burning the metal.
Frequently asked questions (FAQ)
Is it possible to replace a steel compressor with copper?
The concept of a “copper compressor” does not exist, since the housing is always steel. We may be talking about replacing a compressor with steel tubes with a model with copper fittings. Technically this is possible if the mounting dimensions, power and type of refrigerant are the same. However, finding a new compressor with copper leads on sale is becoming increasingly difficult.
Why is the compressor made of steel and not aluminum?
Steel is stronger than aluminum and better withstands the high pressure that is created inside during operation. In addition, steel is cheaper to produce cases by stamping and welding, and also provides better sealing of the weld.
Does rust on the case affect the operation of the refrigerator?
Superficial rust on the outer wall of the “pot” does not affect the operation if it has not eaten through the metal. However, deep corrosion in the area of the weld or tube outlet can lead to depressurization and leakage of freon. In this case, the compressor must be replaced.
What type of solder should be used to solder steel compressor tubes?
For steel, ordinary tin-lead solders are not suitable. Copper-phosphorus solders containing silver (for example, 15%, 30%, 40%) or special high-temperature solders for stainless steel are used. It is necessary to use active flux or soldering in a protective gas environment.
Where is copper located in the compressor?
Inside the compressor, copper is used in the windings of the electric motor. Also, the tubes coming out of the body (in old and expensive models) and the internal heat exchange system (condenser on the back wall) can be copper, although now it is often made of steel.