When a modern refrigerator stops freezing or begins to make uncharacteristic sounds, the first thing the technician looks at is the heart of the unit - the compressor. For most users, that black metal cylinder at the bottom of the case remains a mystery, hidden by a casing and many tubes. However, understanding what is inside the refrigerator compressorhelps equipment owners to better diagnose faults and avoid costly repairs where prevention can be done.
A compressor is a complex electromechanical unit that operates under high pressure. It is this that ensures the circulation of the refrigerant, causing it to pass from a gaseous state to a liquid state and back, removing heat from the refrigerator chambers. The internal structure of this mechanism is designed to last for many years in an aggressive environment where electricity, oil and freon are combined. Let's take a look inside this “black can” to understand how it functions.
Inside the sealed housing there is not just a motor, but a whole system of valves, pistons and electrical windings. Operating principle It is based on gas compression, but the implementation of this process can differ significantly depending on the type of compressor. Understanding the internal architecture is necessary not only for engineers, but also for those who want to extend the life of their home appliances by avoiding critical errors during operation.
Sealed casing: the first line of defense
The outer shell that we see is a welded steel casing. It functions not only as protection, but also as a sealed container for the entire mechanism. An excess pressure of refrigerant vapor is created inside this casing, which eliminates the entry of air and moisture from the outside, which could cause oxidation of parts or freezing of moisture in the capillary pipe. The walls of the casing often have stiffening ribs, and the casing itself is painted with heat-resistant paint to protect against corrosion.
It is important to note that the casing is part of the cooling system of the motor itself. Freon vapors sucked in by the compressor first pass through the internal cavity of the housing, cooling the electric motor windings before entering the compression cylinder. This design allows it to be used refrigerant as an effective cooler for the electrical part of the unit, preventing overheating even during long-term operation.
⚠️ Attention: It is strictly forbidden to open the welded compressor casing at home without special equipment. There may be gas under pressure inside, and oxygen entering the open electrical contacts when connected to the network is guaranteed to lead to an explosion or fire.
Three process tubes are welded to the body: two copper (for suction and injection of refrigerant) and one steel (filling tube, which is sealed after factory filling). Also located outside are electrical contacts, covered with a plastic box, through which voltage is supplied to the motor windings.
Electric motor: the heart of the system
The basis of the internal structure is electric motorwhich drives the piston group. Most household refrigerators use squirrel-cage asynchronous motors. They consist of a stator mounted on springs or rigidly on a housing, and a rotor mounted directly on the compressor shaft. This design ensures a reliable start and stable operation during voltage surges.
The motor stator is a set of metal plates on which two main windings are wound: starting and working. Starting winding has a higher resistance and a smaller number of turns, it turns on only at the moment the rotor starts. The working winding consumes the main current and ensures continuous rotation of the shaft. For the correct operation of this system, a starting relay is used, which opens the starting winding circuit after a set of revolutions.
The engine rotor is mounted on the crankshaft of the compressor. Modern models often use motors with a higher energy efficiency class, which uses higher quality electrical steel to reduce eddy current losses. This allows you to reduce the heating of the motor and reduce energy consumption, which is especially important for refrigerators that operate around the clock.
In inverter models, the motor design is more complex: they use permanent magnet motors and electronic speed control. This allows you to smoothly regulate the speed of rotation of the shaft, avoiding sudden starting currents and reducing noise levels. However, the basic principle - the conversion of electrical energy into mechanical movement of the shaft - remains unchanged.
Crank mechanism and piston group
Directly above the engine rotor, being its continuation, the crankshaft is located. This is the most loaded element of the mechanical part. An eccentric or crank is attached to the shaft, which converts rotational motion into translational motion. It is this unit that is responsible for the movement of the piston inside the cylinder, creating the necessary pressure.
The piston group consists of a cylinder, a piston and a valve plate. The cylinder is usually part of the compressor housing or a separate part into which the piston is inserted. A valve plate with suction and discharge valves is installed at the end of the cylinder. These valves are thin elastic petals that open and close under the influence of pressure differences, allowing gas to pass in only one direction.
Compression mechanism works as follows: when the piston moves down, a vacuum is created, the suction valve opens, and freon vapor enters the cylinder. As the piston moves upward, the volume decreases, the pressure increases, the suction valve closes, and the discharge valve opens, pushing the compressed gas into the condenser. This cycle is repeated dozens of times per second.
Why are pistons made of an alloy?
Pistons are made of light and strong alloys, often coated with graphite, to minimize friction and wear. The use of heavy metals would lead to inertial overloads and rapid destruction of the crank mechanism.
In some types of compressors, for example, rotary ones, instead of a piston, a roller rotor is used, which is pressed against the cylinder wall and moves gas through a crescent-shaped space. However, in classic household refrigerators, it is the piston design that dominates because of its reliability and ability to create high pressure.
Lubricating system and oil separation
One of the critical systems inside the compressor is the lubrication system. Since the compressor operates in a sealed circuit, external oil supply is not possible. Inside the casing there is a special refrigeration oilwhich is mixed with refrigerant. The oil level is strictly controlled at the factory and must always remain within certain limits.
Lubrication of rubbing parts (bearings, cylinder, piston) is carried out by splashing. The lower end of the crankshaft often has an oil pickup or screw thread. When the shaft rotates, the oil rises through the shaft channels upward to the bearings under the influence of centrifugal forces. Then it is sprayed inside the housing, lubricating the remaining components and flowing back into the crankcase.
| Oil type | Refrigerant used | Features |
|---|---|---|
| Mineral | R12, R600a (partially) | Poorly mixed with synthetics, hygroscopic |
| Synthetic (POE) | R134a, R404a, R410a | Highly hygroscopic, requires vacuuming |
| Alkylbenzene (AB) | R134a, R404a | Compatible with mineral residues, less hygroscopic |
It is important to understand that oil should not enter the cooling system in large quantities, as this reduces the efficiency of heat transfer. Therefore, inside the compressor, on the path of the compressed gas exit, oil separators are often installed or special labyrinths are used in the casing, where the oil has time to settle and flow back down before the gas leaves the compressor.
⚠️ Attention: If the compressor was lying on its side for a long time or was turned over, oil could drain into the cooling system circuit. Turning on such a compressor without preliminary settling (at least 24 hours in a vertical position) can lead to water hammer and destruction of the valves.
Vibration insulation and engine mounting
A running compressor is a source of constant vibration. To prevent these vibrations from being transmitted to the refrigerator body and creating noise, the engine and compressor group are suspended inside the casing on special springs. The number of springs is usually three or four, they are located around the perimeter of the internal cavity.
These springs are in an oil bath, which also helps to lubricate them and protect them from corrosion. The suspension design is designed to dampen vibrations both during operation and at the moments of starting and stopping the engine, when inertial loads are maximum. Sometimes the springs are attached to the engine itself, and sometimes to the inner walls of the casing, but the principle remains the same.
When transporting a refrigerator, it is often recommended to secure the compressor with shipping bolts to prevent the engine from swinging inside the casing and breaking tubes or electrical wires. If you are buying a used refrigerator or transporting your own, check with the seller or in the instructions whether the unit needs to be fixed, or whether this model uses a system that allows free suspension.
☑️ Signs of problems with the compressor
Over time, the springs may lose their properties or burst, which will lead to the appearance of a strong noise when the refrigerator is operating. In this case, it is necessary to disassemble the casing and replace the spring assembly, which is a complex repair operation that requires sealing the housing.
Types of compressors: differences in the filling
Although the basic device is similar, the internal filling of compressors may vary depending on the type. The most common are piston compressors, the design of which we discussed above. They are reliable, repairable (partially) and inexpensive to produce. However, there are other solutions on the market.
Rotary compressors they have a rotor inside that rotates in a cylinder. The gas is compressed by changing the volume of the crescent-shaped chamber between the rotor and the cylinder wall. Such units are more compact, quieter and have less vibration, but are more sensitive to the quality of the refrigerant and the presence of liquid at the inlet.
Linear compressors, actively promoted by some manufacturers, are devoid of rotational motion. The piston in them is driven by a linear electric motor, performing reciprocating movements. This eliminates the crank mechanism, reducing friction and wear. There are fewer moving parts inside such a compressor, which theoretically increases reliability.
Inverter compressors can be either piston or another type, but their main difference is the presence of built-in or external control electronics. There may not be radical differences inside the “pot” itself, but they have higher requirements for the quality of winding of the motor and bearings, since they operate in a wide range of speeds.
Frequent breakdowns of internal components
Knowing what is inside the compressor helps to understand the reasons for its failure. One of the most common problems is break or interturn short circuit motor windings. This occurs due to overheating, voltage surges or aging insulation. In this case, the compressor either does not start, or it hums and knocks out the circuit breaker.
Jagging of the mechanical part is the second common reason. It can be caused by a lack of lubrication (oil has leaked into the system or burned out), foreign particles entering the cylinder, or destruction of the bearings. When jammed, the engine hums, the shaft does not rotate, and the thermal relay is activated.
Destruction of the valve plate leads to the compressor working, but not creating the required pressure. The refrigerator stops freezing, although the motor runs continuously. This often happens when working with substandard refrigerant or when overheated, when the metal of the valves loses its elasticity.
Is it possible to revive a jammed compressor?
There is a method of “wedging” by applying increased voltage or mechanically turning the shaft, but success is less than 20%. Most often, such a procedure only finishes off the mechanism, so replacing the unit is preferable.
A “breakdown to the housing” also occurs, when the insulation of the windings is broken and the electric current begins to pass to the metal casing. This is deadly for the user. You can check this with a multimeter by measuring the resistance between the contacts and the copper tube - it should be infinite.
FAQ: Frequently asked questions
Is it possible to replace the compressor in the refrigerator yourself?
Theoretically, it is possible, but this requires special tools: a burner, a vacuum pump, pressure gauge station and copper pipe soldering skills. In addition, it is necessary to know exactly the type and quantity of oil and refrigerant. Without sealing and vacuuming, the system will not work for a long time.
Why is the compressor hot to the touch?
The operating temperature of the compressor casing can reach 70-90 degrees Celsius, which is normal. This is due to the fact that the gas is compressed inside, the temperature of which rises, and the windings of the electric motor heat up. If the temperature is higher or there is a burning smell, this is a sign of a malfunction.
How much does a refrigerator compressor weigh?
Weight depends on the model and power. Standard household compressors weigh between 8 and 12 kg. Industrial or compressors for large two-chamber refrigerators can weigh up to 20 kg. Inside, the main mass is made up of metal windings and a steel body.
What to do if the compressor clicks and does not start?
Most likely, the starting relay has failed or the engine is jammed. First, it is worth replacing the relay (this is an inexpensive part), since it is often the cause of clicking. If replacement does not help, there is probably a problem in the windings or mechanics of the compressor itself.
Can a compressor from a refrigerator be used for other purposes?
Yes, old compressors are often used to create homemade compressors for airbrushing, inflating tires or pneumatic tools. However, you need to remember that they are designed to work with freon, not air, and require modernization of the lubrication and filtration system.