The refrigeration compressor is often called the heart of household appliances, but few people think about what is hidden inside this sealed metal case. Outwardly, it is just a black or gray “pear” with tubes, but inside it hides a complex mechanical assembly that operates under high pressure. Understanding what is inside is necessary not only for professional craftsmen, but also for those who want to understand the causes of breakdown or noise.
There is a vacuum inside the case, and the mechanism itself is immersed in a special oil. Tightness is a key requirement, the violation of which turns the unit into a pile of metal. If you hear a knocking, grinding noise, or see that the compressor has stopped starting, the problem lies precisely in the internal mechanics. Let's look under the cover to understand exactly how this important element works.
It is worth noting right away that modern models are practically impossible to repair at home due to the complexity of assembly and the need to vacuum the system. However, knowledge of the device will help you more accurately diagnose the malfunction and understand why replacing the compressor is often the only solution.
Principle of operation and general design
The main task of the compressor is to compress the refrigerant and circulate it around the refrigerator circuit. Inside the housing there is electric motorwhich drives the piston group. This entire system is suspended on special springs that dampen vibrations and prevent noise transmission to the outer casing.
The operating cycle begins with the supply of electricity to the motor windings. The rotor begins to rotate, transmitting torque to the crankshaft. This shaft, in turn, causes the pistons to move up and down, drawing freon gas from the evaporator and compressing it to be released into the condenser.
⚠️ Attention: High pressure is maintained inside the compressor, even when it is turned off. Do not attempt to open the housing without special equipment and skills, as this may result in metal rupture or release of residual oil.
The design is designed to minimize friction and wear of parts. The oil located at the bottom of the tank sprays out when the shaft rotates, lubricating all rubbing surfaces. That is why it is important to prevent the compressor from operating without refrigerant or with a leak.
Electrical part: stator and rotor
The heart of the engine is electric motorconsisting of a stationary stator and a rotating rotor. The stator is a package of metal plates on which copper windings are wound. Their quality and integrity directly affect the engine's ability to start and operate under load.
The rotor is mounted directly on the crankshaft and rotates inside the stator. Modern asynchronous motors use a squirrel-cage rotor that does not have brushes, which significantly increases the service life of the unit. The windings are made of copper wire coated with heat-resistant varnish that can withstand heat.
- 🔌 Starting winding — creates an initial torque to start the shaft.
- ⚙️ Working winding —supports rotor rotation in normal mode.
- 🛡️ Thermal protection —a bimetallic plate that breaks the circuit when overheated.
During overloads or voltage surges, breakdown of the winding insulation may occur. In this case, the engine hums, but does not rotate, or the circuit breaker knocks out. Checking the resistance of the windings with a multimeter is the first step in diagnosing the electrical part.
How to check the windings with a multimeter?
To check, you need to remove the start-up relay. The resistance between the contacts of the working and starting windings should be within 10-30 Ohms. The resistance between the windings and the housing should tend to infinity. If it shows zero or very little, the winding is burned out or shorted to the housing.
Mechanical part: crank mechanism
It is the mechanics that converts the rotational movement of the shaft into the translational movement of the piston. Crank mechanism is a complex system that requires high manufacturing precision. Any wear or deformation here leads to knocking and decreased performance.
The crankshaft has eccentrics on which the connecting rods are placed. When the shaft rotates, the connecting rods perform oscillatory movements, pushing the pistons inside the cylinders. In household refrigerators, a one- or two-piston system is most often used, where the pistons are located vertically.
| Part | Material | Function | Signs of wear |
|---|---|---|---|
| Crankshaft shaft | Steel | Rotation transmission | Knock, vibration |
| Connecting rod | Aluminium/Steel | Shaft connection and piston | Backlash, knock |
| Piston | Steel | Gas compression | Cold reduction |
| Bearings | Bronze/Steel | Shaft support | Noise, jamming |
Particular attention should be paid to plain bearings. They work in an oil bath, but if moisture or oil breakdown products get in, they can tear up the shaft. This often leads to a wedge in the motor when it hums, but it is impossible to move the shaft.
Valve group and suction system
The efficiency of freon compression depends on the tightness of the valve group. Inside the cylinder head there are suction and discharge valves. They are thin metal plates that open and close under the influence of gas pressure.
When the piston moves down, the suction valve opens and freon vapor enters the cylinder. When the piston moves upward, this valve closes and the discharge valve opens, releasing compressed gas into the system. Springs or the elasticity of the plates themselves ensure timely closure.
☑️ Signs of valve malfunction
If the valve plate breaks or becomes deformed, the compressor stops creating the required pressure. Freon begins to simply flow from one side to the other without compression. Visually, this is manifested in the fact that the motor runs constantly, but the refrigerator does not gain temperature.
Valve defects often occur due to water hammer when liquid freon enters the cylinder instead of gas. Also, the reason may be a factory defect or a long-term lack of maintenance of the system.
Oil system and lubrication of components
Located in the lower part of the housing compressor oil. It performs several functions: lubricates rubbing parts, removes heat and ensures tightness of the gaps between the piston and cylinder. The oil level is strictly regulated by the manufacturer.
Lubrication is carried out by splashing. The lower end of the crankshaft often has a scoop or screw thread that captures oil and forces it up the shaft to the bearings. From there it drains, lubricating the remaining components, and returns to the crankcase.
⚠️ Attention: It is strictly forbidden to mix different types of oils (mineral and synthetic). This leads to the formation of sediment, which clogs the capillary tube and disables the refrigerator.
Over time, the oil may oxidize, especially if the system has been overheated. It loses its properties, becomes viscous or, conversely, too liquid. Changing the oil at home is almost impossible without a complete overhaul and vacuuming of the compressor.
Sealed housing and shock absorption
The entire mechanism is enclosed in sealed steel casing, consisting of two hemispheres welded along the equator. A vacuum is created inside, which facilitates engine operation and prevents freon leaks. The housing also serves as a reservoir for oil.
The engine with the mechanism is suspended inside the casing on three or four springs. This shock absorption system is critical. If the spring bursts or jumps off, you will hear a loud metallic clang and knock when starting and stopping the engine.
The vibration is transmitted to the body, but thanks to the suspension it is damped. However, if the refrigerator is installed incorrectly (not level), the load on the springs may become uneven, which will lead to their premature failure.
Frequent breakdowns of internal components
Despite reliability, internal parts wear out. The most common electrical problems are interturn short circuits or broken windings. Mechanical failures, such as shaft scuffing or connecting rod failure, occur less frequently, usually after prolonged use or operation without freon.
Another common problem is the destruction of the valve plate. This causes the compressor to run idle. Oil leaks through the shaft seals are also possible if the design of the compressor allows this (although this is rare in hermetic compressors).
- 🔥 Overheating - destroys the insulation of the windings and the properties of the oil.
- 🔨 Water hammer - breaks valves and connecting rods when liquid gets in.
- 💧 Moisture —causes corrosion and freezing in the system.
Diagnosis of internal failures is often carried out indirectly: by current consumption, case temperature and output pressure. An accurate diagnosis can be made only after opening, which usually means disposal of the unit.
Is it possible to change the oil in a refrigerator compressor?
Theoretically it is possible, but in practice it is not practical. To replace it, you need to open the case, which breaks the seal. After this, professional welding, vacuuming and filling are required. It is easier and cheaper to buy a new compressor than to try to revive an old one with an unknown internal state.
Why does the compressor hum but does not start?
Most often the reason is a jammed mechanical part (the shaft cannot turn) or a faulty start relay. If the hum is strong and short-lived, and then there is a click, the thermal protection is triggered. This may be due to the lack of freon (nothing to pump) or a mechanical wedge.
Is it dangerous to open an old compressor for the sake of metal?
Yes, it is dangerous. Pressure may remain inside, as well as oil and freon vapors. When sawing with a grinder, oil vapors may ignite or fragments may fly away under pressure. In addition, old compressors may contain asbestos in the gaskets, the dust from which is harmful to the lungs.