When the usual hum suddenly stops in the house or, conversely, an unusual rumble begins to irritate us, we think about what makes the refrigerator work. The heart of this complex unit is the compressor, which in everyday life is often simply called the engine. Understanding what exactly it is made of helps not only to have a deeper understanding of technology, but also to better assess the cost of repairs or the need to replace the unit.
The design of this mechanism seems simple only at first glance, but high-precision engineering is hidden inside the steel case. Materials and components are selected to withstand enormous changes in temperature and pressure for decades. Let's figure out which elements ensure the circulation of the refrigerant and why the quality of their performance directly affects the service life of your refrigeration equipment refrigeration equipment.
Casing materials and external protection
The outer shell of the compressor is not just a jar for storing internals, but an important element of the safety and sound insulation system. Traditionally, the body is made of two stamped halves made of high-strength low-carbon steel. These halves are connected to each other by arc welding, which ensures the tightness necessary for working under high pressure.
Steel was not chosen by chance: it is strong enough to withstand the internal pressure of freon, which can reach several atmospheres, especially at the time of start-up or when working in hot climates. The metal surface is often phosphated or coated with special anti-corrosion compounds to prevent rusting when in contact with condensation or humid kitchen air.
⚠️ Attention: The compressor housing can heat up to 90-110 degrees Celsius during operation. Never touch a running or just switched off unit with bare hands to avoid burns.
The outlet pipes are located on the top of the housing. One of them, usually of a larger diameter, serves to suck gaseous refrigerant from the evaporator, and the second, of a smaller diameter, pumps compressed gas into the condenser. These tubes are often made of copper alloys or copper-plated steel, which facilitates soldering during repair or assembly.
Why cannot the housing be opened?
Refrigerator compressors are of the closed type. This means they are sealed at the factory forever. Opening the housing at home without special equipment and skills is impossible: the seal will be broken, volatile lubricant components will escape, and it will no longer be possible to assemble it back to factory quality.
Electric motor: stator, rotor and windings
Inside the steel casing the electric motor itself is hidden, which drives the piston group. The basis of the electromagnetic system is stator a stationary part assembled from thin plates of electrical steel. Such a layered structure is necessary to minimize energy losses due to eddy currents, which inevitably arise when working with an alternating magnetic field.
Copper windings are laid in the stator slots. It is copper used due to its exceptional electrical conductivity. The winding is divided into two parts: starting and working. The starting winding has a higher resistance and is made of thinner wire; it is needed only at the moment of start to create the initial torque. The working winding is thicker and is designed to constantly maintain rotation.
The rotating part of the motor is rotor, which is also made of electrical steel plates. Most household refrigerators use squirrel-cage asynchronous motors. Aluminum or copper poured into the rotor forms a “squirrel cage” in which currents are induced, creating a magnetic field that interacts with the stator field.
Crank mechanism and piston group
The heart of the mechanical part of the compressor is the crank mechanism, which converts the rotational movement of the rotor into the reciprocating movement of the piston. The compressor shaft, which is a continuation of the rotor, has an eccentric or cranked shape. This element experiences enormous mechanical loads and is made of high-strength alloy steels that have been hardened.
A connecting rod is attached to the shaft, which connects the rotating part to the piston. Modern compressors often use a design where the connecting rod and piston are a single piece or pinless to reduce friction. The piston that moves inside the cylinder is also made of durable metal, often coated with graphite to improve sliding.
The cylinder in which the piston moves is part of a stationary block called the cylinder block. The precision of machining the inner surface of the cylinder must be micron. Any scuffs or scratches will lead to a loss of compression and ineffective operation of the refrigerator. The materials used here are the same as for the rest of the mechanics - hardened steel or special cast iron alloys.
Valve system and flow distribution
The valve mechanism is a critically important component on which the refrigerator’s ability to create cold depends. It is located directly at the end of the cylinder and consists of the thinnest metal plates - petal valves. These valves operate as automatic dampers, opening and closing under the influence of pressure differences.
The suction valve allows freon gas from the return tube into the cylinder as the piston moves downward. The discharge valve opens as the piston moves upward, releasing the compressed gas into the condensation system. For the manufacture of these plates, a special spring steelis used, which has high elasticity and resistance to fatigue (metal fatigue).
The valve plate is pressed against the valve seat with a certain force. If the clamping force is too high, the compressor will have difficulty pumping gas (performance loss). If it is too small, gas will leak back and the refrigerator will stop freezing. Adjusting this gap and the condition of the plates is one of the most delicate operations during repair.
Oil system and lubricants
Not a single internal combustion engine or compressor can operate without lubrication, and a refrigeration unit is no exception. Inside the sealed casing, in its lower part, there is always a certain amount refrigeration oil. This oil differs from automobile oil: it has properties such as low pour point and chemical compatibility with refrigerants and sealing materials.
Depending on the type of freon, different types of oils are used. For old freons (R12), mineral oils were used, for modern ones (R134a, R600a) - synthetic oils, such as polyol ether (POE) or alkylbenzene (AB). Mixing different types of oils is strictly prohibited, as this can lead to the formation of acids, varnish deposits and blockage of the capillary system.
Lubrication of rubbing parts occurs by splashing. At the end of the compressor shaft there is often a special tube or spiral that, when rotated, captures oil from the bottom of the crankcase and sprays it onto the cylinder walls, bearings and connecting rod. Some of the oil circulates along with freon through the system, so it must be well dissolved in the refrigerant so as not to clog narrow channels.
| Refrigerant type | Type of compatible oil | Features |
|---|---|---|
| R12 (Freon-12) | Mineral (MO) | Highly hygroscopic, afraid of moisture |
| R134a | Polyester (POE) | Very hygroscopic, requires quick replacement |
| R600a (Isobutane) | Mineral / Alkylbenzene | Explosive if leaked, requires caution |
| R410A / R32 | Polyester (POE) | High operating pressure, synthetics |
Starting system and electrical components
Although the starting relay is often located outside the compressor housing, it is an integral part of the engine control system. Inside the relay there are two key elements: a starting relay (electromagnetic or posistor) and a thermal protection relay. A posistor, for example, is made of special ceramics that changes resistance when heated.
When voltage is applied, current passes through the starting winding and the posistor. The posistor heats up, its resistance increases sharply, and the current through the starting winding practically stops - the motor continues to operate only on the working winding. If the motor overheats or the current exceeds the norm, the bimetallic plate of the thermal relay opens the circuit, saving the motor from combustion.
The electrical contacts inside the relay are made of silver or special alloys that are resistant to sparking. With frequent switching on and off, carbon may form on the contacts, which leads to sticking or, conversely, lack of contact. Replacing a relay is one of the most common and simplest procedures in refrigerator repair.
☑️ Diagnosing a compressor malfunction
Frequently asked questions (FAQ)
Is it possible to replace the motor-compressor with an analogue from another manufacturer?
Yes, this is often possible, but careful selection of parameters is required. It is important to consider the power (in BTU or hp), the type of refrigerant, the height of the start and discharge tubes, and the overall dimensions. It may also be necessary to replace the filter drier and starting relay to suit the characteristics of the new motor.
Why does the compressor hum but does not start?
This may indicate several problems: jamming of the mechanical part (piston), failure of the starting relay, or breakage of the starting winding. Also, the reason may be low voltage in the network, due to which the engine does not have enough power to take off.
How much oil is inside the compressor?
The amount of oil is strictly regulated by the manufacturer and usually ranges from 150 to 300 grams, depending on the model. A lack of oil will lead to scuffing and overheating, and an excess will cause water hammer and a drop in performance, since the oil will occupy the volume intended for gas.
What is an inverter compressor and how does it differ in design?
In an inverter compressor, a DC motor does not have a strict connection between the rotational speed and the mains frequency. It can smoothly change the speed of rotation of the shaft, which allows you to more accurately maintain the temperature and save energy. Structurally, they are often made according to a linear scheme, where the piston is driven directly by an electromagnetic field, without a rotational mechanism.