Anatomy of cold: what is the refrigerator motor made of

When you open the refrigerator door and feel the coolness, you rarely think about what makes this cold circulate inside the chambers. The heart of the entire system is the compressor, which in everyday life is often called a motor. This is a complex engineering device hidden in a black metal casing on the back wall of the unit. Understanding what the refrigerator motor is made ofis necessary not only for design engineers, but also for repairmen, as well as inquisitive equipment owners.

The design of a modern compressor is a sealed block, inside of which a vacuum or inert gas reigns, and all mechanical parts are immersed in a special oil Sealed housing protects internal components from moisture and dust, which is critical for the long service life of the device. If water got inside, it would instantly freeze in the narrow channels of the capillary tube, causing a blockage of the system.

In this article we will analyze in detail the materials used in the production of the main components and explain the physical principles underlying their operation. You will learn why copper is more valuable than aluminum in windings, what role steel plays in the piston group and why modern inverter models are more complex than classic ones.

Case materials and external protection

The first thing that catches your eye when examining the back of the refrigerator is the black, smooth “barrel”. This is an outer casing that serves not only as a decorative element, but also as a powerful sound insulator. It is made from stamped steel, most often low-carbon material, which has good ductility and strength. Two hemispheres are welded together along the equator, forming a sealed capsule.

Inside this steel shell is the compressor unit itself, suspended on springs. Springs are needed to dampen vibrations that occur during engine operation. If the motor were rigidly fixed to the bottom of the casing, the noise would be heard throughout the kitchen. The steel of the case also serves as a heat exchanger: condenser tubes passing outside (in some models) or simply a heated case give off heat to the environment.

• 🔩 Low carbon steel is the main material for stamping the casing, ensuring tightness.
• 🛡️ Epoxy coating - is applied to the outer surface to protect from corrosion and scratches.
• 🔊 Rubber dampers —used in places where springs are attached to reduce noise.

⚠️ Attention: Never try to open the sealed compressor casing at home without special equipment. There may be residual freon pressure inside, and moisture getting inside the motor when opened will lead to its immediate failure the next time you turn it on.

The thickness of the walls of the steel casing varies, but is usually several millimeters. This is sufficient to withstand internal pressure and mechanical stress during transportation. It is important to understand that this housing is the last line of defense for complex internal mechanisms.

Electrical part: the heart of the engine

Looking inside the casing, we will see the electric motor that drives the piston group. The basis of the electrical part is stator i rotor. The stator is a set of electrical steel plates folded into a package. This design was not chosen by chance: thin plates isolated from each other make it possible to minimize energy losses due to eddy currents, which inevitably arise in an alternating magnetic field.

Copper windings are laid in the stator slots. Copper is used due to its high electrical conductivity. In cheap or older models, aluminum windings could sometimes be found, but they are less reliable and have higher resistance, which leads to overheating. The winding consists of two parts: starting and working. The starting winding has a smaller wire cross-section and more turns, which creates the necessary phase shift to start rotor rotation.

The engine rotor is a cylinder, also made of steel plates, with a “squirrel wheel” filled with aluminum or copper. When current is applied to the stator windings, a rotating magnetic field is created, which drags the rotor along with it. The critical parameter here is the quality of the varnish insulation of the windings, since it must withstand high temperatures and the aggressive effects of refrigerant and oil vapors.

• ⚡ Electrical steel —used for the stator and rotor core to reduce magnetic losses.
• 🧶 Copper wire —winding material with (heat-resistant) enamel insulation.
• 🌡️ Thermal relay —a bimetallic plate that protects the windings from overheating.

To start the engine, a starting relay is connected to the circuit. In older models it was a relay with a posistor (a ceramic element that changes resistance when heated), in new ones it was electronic components. The relay automatically turns off the starting winding when the engine picks up speed, leaving only the main winding to work.

Mechanical part: compressor unit

The electric motor itself does not create cold, it only creates mechanical movement. A crank is eccentrically attached to the rotor shaft, which converts rotational motion into translational motion. Attached to the crank is a piston that moves inside the cylinder. It is this pair - cylinder and piston - that is the main working body of the compressor.

The materials here are selected taking into account friction and pressure. The cylinder is often made of cast iron or special hardened steel. The piston can be aluminum or steel. There should be a minimum gap between them, but they should not touch each other during operation to avoid scuffing. Lubrication of the rubbing pairs is provided by oil, which is sprayed by a rotating shaft or supplied under pressure.

A valve plate is installed on top of the cylinder. This is the thinnest part made of hardened steel or a special composite material. There are holes made in it, closed by petal valves. These valves work as valves (check valves), allowing gas to pass in only one direction: from the evaporator to the cylinder and from the cylinder to the condenser.

In modern linear compressors, the design is simplified: there is no rotating shaft and crank. The piston moves back and forth directly from the electromagnet. This reduces the number of rubbing parts and increases energy efficiency, although it adds complexity to the control system.

Lubricating system and coolant

It is impossible to talk about what the motor is made of without mentioning the fluids that circulate in it. Inside the sealed casing there is compressor oil. This is not ordinary engine oil, but a special synthetic composition, which must be chemically inert with respect to the refrigerant (freon) and seal materials. If the oil thickens in the cold or reacts with freon, the refrigerator will stop working.

Freons (R134a, R600a) are most often used as a refrigerant. Isobutane (R600a) is a natural gas that has excellent refrigeration properties, but is explosive in high concentrations. That is why there is a warning sticker on the back wall of refrigerators containing this gas. The amount of oil and freon is calculated by the manufacturer to the nearest gram.

What happens if you mix different oils?

Mixing mineral and synthetic oil can lead to the formation of a sediment that will clog the capillary tube. It is also possible that the viscosity of the mixture will change, which will lead to jamming of the compressor or overheating.

The lubrication system in piston compressors is often implemented through a shaft. A channel is drilled into the shaft, which takes oil from the bottom of the crankcase and sprays it onto the cylinder bore and bearings due to centrifugal force. In linear compressors, oil is supplied by a pump or sprayer connected to the piston.

⚠️ Attention: When replacing a compressor, it is strictly forbidden to leave the system open for more than 15-20 minutes. Hygroscopic oil instantly absorbs moisture from the air, which will lead to the formation of acids inside the system and destruction of the winding insulation.

Inverter technologies: difference from the classics

Traditional refrigerators operate on the “on-off” principle. The motor either runs at full power or rests. Inverter models are designed differently. They use inverter an electronic unit that converts alternating current from the network into direct current, and then again into alternating current, but with a variable frequency. This allows you to smoothly regulate the motor rotation speed.

Inverter compressors often use motors with permanent magnets on the rotor (neodymium magnets). This allows you to make the motor more compact and efficient. The absence of frequent starts and stops (which is the most stressful mode for mechanics) significantly extends the service life of the device. However, the electronic filling of such motors is more sensitive to power surges in the network.

• 🧲 Neodymium magnets — used in the rotors of inverter motors to create a powerful field.
• 💻 Control board (inverter) —microprocessor unit that regulates the rotation speed.
• 📉 Temperature sensors —transmits data to the board for precise power adjustment.

Inverter motors are quieter, more economical and maintain temperature more accurately. However, their repair is more difficult and more expensive, since it requires not only mechanical intervention, but also in-depth diagnostics of the electronics.

Typical malfunctions and their causes

Understanding the design helps diagnose breakdowns. If the refrigerator hums but does not cool, there may be a problem in valve plate or the piston group. If the motor hums and clicks, but does not start, the starting relay or an interturn short circuit in the winding is often to blame. An interturn short circuit occurs when the varnish insulation of the wires becomes thinner, and the turns close together, causing a short circuit.

Jagging of the mechanical part is the nightmare of any compressor. This happens when the oil loses its properties, burns out or becomes contaminated with decay products. The piston is tightly stuck to the cylinder. In this case, the motor tries to turn the shaft, consumes a huge current and burns out if the thermal relay does not work.

Also often encountered is a broken piston rod in linear compressors. The plastic or metal, unable to withstand the load, breaks and the piston stops moving, although the engine continues to hum. Repair in such cases is usually impractical; a complete replacement of the unit is required.

Frequently asked questions (FAQ)

Is it possible to replace the copper winding with aluminum during repairs?

Theoretically it is possible, but this requires recalculating the number of turns and the diameter of the wire, so as the conductivity of aluminum is lower. In practice, rewinding of refrigerator compressors is almost never done due to the complexity of sealing and high labor intensity. It is cheaper and more reliable to buy a new compressor.

Why is the compressor hot to the touch?

When gas is compressed, its temperature always increases (this is a law of physics). In addition, the motor heats up due to the passage of electric current through the windings. A housing temperature of 50-70°C is considered normal operating temperature. If it is hot to the point that you cannot touch it, this is a sign of a malfunction.

How many years does a modern refrigerator motor last?

The average service life of a compressor is 10-15 years. According to manufacturers, inverter models can operate for up to 20 years or more due to the absence of starting loads. However, the real life time depends on the quality of the voltage in the network and operating conditions (dust, room temperature).

Is it dangerous to open the compressor for disposal?

Yes, it is dangerous. Pressure and freon vapor may remain inside. In addition, the oil is toxic. Compressors should be disposed of at specialized scrap metal collection points, where there is equipment for the safe release of gases and drainage of technical liquids.