When an old refrigerator stops freezing or starts humming like a tractor, most owners immediately think of the compressor. It is this unit that is often called the “heart” of the refrigeration system, and not without reason. Refrigeration compressor is responsible for the circulation of refrigerant throughout the circuit, creating the necessary pressure for cooling. However, few people think about what is inside this black metal “barrel” welded to the rear wall of the unit.
Understanding the internal structure helps not only in diagnosing malfunctions, but also in an informed approach to the operation of equipment. Inside the sealed housing there is a complex mechanical system operating under high pressure. Hermetically sealed piston compressors, which make up the lion's share of the household appliance market, have a single basic design, although they may differ in design nuances from different manufacturers.
In this article we will look in detail at what exactly hidden behind the casing welds. You will learn how electrical energy is converted into mechanical movement, and then into cold. Disassembling the compressor - the process is complex and often irreversible, so theoretical knowledge here is more important than practical opening skills if you do not plan to engage in professional repairs.
Purpose and operating principle of a sealed compressor unit
The main task of the compressor is to compress refrigerant vapors and pump them through the pipeline system. This process ensures a continuous heat exchange cycle. Without creating a pressure difference in the circuit, evaporation of freon in the fridge compartment would be impossible. Compression (compression) is a physical process that requires significant energy expenditure, which in domestic conditions is taken from the electrical network.
The principle of operation is based on the transformation of the rotational movement of the shaft electric motor into the forward movement of the piston. This allows low pressure gas to be captured from the evaporator and forced into the condenser at high pressure. It is important to understand that there are no electronically controlled open valves or dampers within the system; all processes are regulated by the physics of gases and the mechanics of the valve group.
⚠️ Attention! There is always oil mixed with refrigerant inside the compressor. If the housing is depressurized (cut or drilled), the oil will leak out and the freon will evaporate. It is almost impossible to restore factory tightness and recharge the system at home without special equipment.
Modern models, especially inverter ones, may have a slightly modified internal architecture to reduce noise and vibration. However, the basic elements remain unchanged for decades. Electromechanical connection between the motor and the pumping part is a critical point of reliability of the entire unit.
Electric motor: source of mechanical energy
At the bottom of the casing there is an electric motor, which is a fundamental part of the structure. In household refrigerators asynchronous motors alternating current is widely used. Their design is simplified as much as possible to ensure reliability and long-term operation without maintenance.
The motor consists of two main parts: a stator and a rotor. The stator is rigidly fixed to the inner surface of the casing or to a special spring suspension. The rotor, in turn, is pressed onto a shaft, which drives the crank mechanism. The stator windings are made of copper wire with heat-resistant insulation that can withstand heating to high temperatures.
To start the engine, a special starting winding is used, which is turned on only at the time of start. As soon as the rotor reaches the required speed, the centrifugal mechanism or electronic relay turns off the starting winding. Working winding continues to power the engine in normal mode. An imbalance between these windings leads to humming or impossibility of starting.
- 🔌 Stator is the stationary part of the engine that creates a magnetic field.
- 🌀 Rotor is the rotating part that transmits torque to the shaft.
- 🔥 Thermal protection —a bimetallic plate that opens the circuit when the windings overheat.
- ⚡ Start relay —a device that switches the starting winding (often placed outside, but electrically connected).
The quality of winding and balancing of the rotor directly affects the noise level. If the rotor is skewed or the bearings are worn out, vibration is transmitted to the housing, causing a characteristic rattling sound. Electrical part The compressor is sealed and is surrounded by freon vapor and oil, which helps cool the windings.
Crank group and piston system
The heart of the mechanical part is the crank group (CSG). It is this unit that transforms the rotation of the engine shaft into the reciprocating movement of the piston. The design of the CSHG in refrigeration compressors has its own characteristics that distinguish it from automobile engines.
The compressor shaft has an eccentric journal or a crank attached to it. The connecting rod surrounds this journal through a plain bearing (liner) or needle bearing. When the shaft rotates, the connecting rod begins to make oscillatory movements, pushing the piston up and down inside the cylinder. Piston group Must have minimal clearances to ensure compression, but sufficient for oil circulation.
The cylinder in which the piston runs is usually part of the pump housing (cylinder block). In some models, piston rings are put on the piston, in others, a ringless design is used, where tightness is achieved due to minimal clearance and oil viscosity. Oil wedge plays a decisive role here, preventing metal scuffing.
⚠️ Attention! Wear of the connecting rod bearing or the appearance of wear on the cylinder surface leads to a drop in compressor performance. The refrigerator stops gaining temperature, although the compressor works continuously.
The materials used in the CSHG are selected to minimize friction. Cast iron, steel and special anti-friction alloys are often used. Any metal shavings that get into this area can quickly damage the unit, causing jamming.
Why are there no rings in the compressor?
In most household refrigeration compressors there are no piston rings. Tightness is ensured by very small gaps (several microns) and an oil film. This reduces friction and simplifies the design, but requires high-quality oil and cleanliness of the system.
Valve system and gas distribution
The valve mechanism is responsible for one direction of refrigerant flow. It is located directly above the cylinder and is a thin plate with petals. These petals work like automatic valves, opening and closing under the influence of pressure differences.
When the piston moves down, a vacuum is created in the cylinder. Under the influence of this vacuum, the suction valve opens and freon vapor flows from the evaporator. When the piston moves upward, the pressure in the cylinder increases, the suction valve closes, and the discharge valve opens, releasing compressed gas into the condenser. Valve plate This is a critical element, the condition of which determines the efficiency of the entire refrigerator.
Valve breakdown (crack, deformation petal) leads to the fact that the gas begins to flow back. The compressor works, but does not pump. No pressure is created in the system and no cold is generated. Replacing the valve plate is theoretically possible, but requires ideal cleanliness and precision assembly.
| Valve element | Function | Symptoms of malfunction |
|---|---|---|
| Suction valve | Starts gas from evaporator | Reduced cooling capacity |
| Discharge valve | Releases gas into the condenser | Pressure drop, overheating |
| Valve spring | Ensures the return of the petal | Knock, violation of operating cycles |
| Plate (tongue) | Direct channel closure | Complete absence of compression |
The valve material is usually a special spring steel. Over time, the metal may become tired or become covered with a varnish coating from oil combustion, which impairs its mobility. Tightness of valves is the key to efficient operation of the refrigeration cycle.
Lubricating and cooling system of internal parts
Unlike automobile engines where there is a separate oil pump; in a refrigeration compressor, the lubrication system is often passive or combined. The oil is located at the bottom of the casing, and its level is strictly standardized. When the engine is running, oil is sprayed out by rotating parts.
In more advanced models, there is a helical groove or scoop at the lower end of the shaft. When the shaft rotates, oil is captured and supplied through a channel inside the shaft to the bearings and piston group. Oil circulation It is necessary not only for lubrication, but also to remove heat from rubbing pairs.
Special synthetic or mineral oil is used, which has good miscibility with freon and a low pour point. If the oil loses its properties (oxidizes, thickens from moisture), the compressor will jam. Oil film is also involved in sealing the gaps between the piston and the cylinder.
- 💧 Oil sump is the lower part of the casing where the main supply of oil is stored.
- 🌀 Scoop or screw —an element on the shaft for lifting oil.
- 🛢️ Specialized oil —liquid with properties for working with refrigerants.
- 🌡️ Heat sink —oil helps cool the windings and mechanics.
⚠️ Attention! Mixing different types of oils (mineral and synthetic, or oils for different types of freon) is strictly prohibited. This can lead to the formation of acids, varnish deposits and rapid failure of the compressor.
It is important to note that some of the oil always circulates along with freon through the system. To return oil to the compressor, the system has loops and pipeline slopes. If the oil in the compressor becomes too low, dry friction and rapid wear will begin.
☑️ Signs of problems with lubrication
Casing, suspension and external elements
All the mechanisms described above are enclosed in a steel casing, which consists of two hemispheres welded together. The casing performs several functions: it seals the system, serves as an oil reservoir and a noise muffler. Internal pressure in the casing it can be either higher than atmospheric or lower, depending on the design and type of refrigerant.
The engine and compressor part are suspended inside the casing on springs This spring suspension damps vibrations that occur during operation of the piston. If a spring breaks or comes off, you will hear a loud metallic clanging sound when starting and stopping the unit. In some older models, the suspension may be external, but in modern household refrigerators it is almost always internal.
On the outside, pipes are welded to the casing: suction (thicker, often without soldering or with a characteristic bend) and discharge (thinner, goes to the condenser). There may also be a process pipe for filling, which is sealed after the factory. Tightness of welds is a key factor in durability.
The surface of the casing is often finned or painted black for better heat transfer, although the main role in cooling is played by the air flow around and the refrigerant inside. Any dent on the casing is dangerous because it can disrupt the clearances inside or damage the springs.
Diagnostics and the possibility of repairing internal components
Is it possible to repair the insides of a compressor? Theoretically, yes, but in practice this is rarely economically feasible for a household user. Replacing valves or connecting rod bearing requires cutting the casing, thorough washing, replacing parts, reverse welding, vacuuming and refueling.
Most often the electrical part is subject to repair: replacing the start relay, thermal protector or interturn short circuit (although the latter is often fatal). Mechanical failures, such as cylinder scuffing or shaft breakage, usually lead to a complete replacement of the unit. Herbetic block not intended for disassembly in service centers.
Diagnostics are carried out by indirect methods: listening to sounds, measuring current consumption, checking resistance windings If the compressor is “clogged” (jammed), sometimes the method of “boosting” by applying increased voltage helps, but this is a temporary measure. Compressor life usually 10-15 years, after which wear becomes critical.
Why is a compressor called sealed?
The term “hermetic” means that the compressor housing is welded at the factory and does not require disassembly during operation. All internal parts operate in a refrigerant and oil environment, which eliminates leaks through the seals, but makes repairs difficult.
Is it possible to replace the compressor with an analogue of another brand?
Yes, it is often possible. The main thing is the coincidence of refrigeration performance, overall dimensions, type of refrigerant and oil, as well as electrical characteristics. However, it is better to install original models or their direct analogues.
What does a humming compressor mean?
A humming sound may indicate a faulty start relay, jammed mechanical parts, unbalanced rotor or separation of the internal suspension spring. An accurate diagnosis is made after opening or replacing the relay.
How long does the compressor operate normally?
In normal mode, the compressor operates cyclically: it turns on, cools the chamber to the set temperature and turns off. The operating and downtime time depends on the load of the refrigerator, the ambient temperature and the thermostat settings.
Is it dangerous to open the compressor at home?
Yes, it is dangerous. Pressure may remain inside, and refrigerant vapors, when in contact with an open flame (during soldering), form toxic compounds. In addition, special equipment is required for evacuation and filling.