The compressor is the heart of any refrigeration unit, ensuring the circulation of the refrigerant in a closed circuit. It is this unit that creates the necessary pressure for condensation and evaporation of freon, allowing heat to be removed from the chambers. In household models, most often there are sealed units, the internal structure of which is hidden from the eyes of the master.
Understanding what is inside the housing is critical for diagnosing malfunctions, such as jamming or winding burns. Disassembling a sealed unit is a complex process that requires special tools and compliance with safety precautions, since the design does not imply reassembly in the factory.
In this article we will take a detailed look at the internal architecture of the motor-compressor, analyze the functions of the main components and describe the technology for opening the housing for troubleshooting. Attention: work is carried out only when completely disconnected from the network equipment.
Schematic diagram and design of the motor-compressor
Inside the steel casing there is an electric motor and a compressor piston group operating in a single unit. The engine shaft is directly connected to the crank mechanism, which converts rotational motion into linear motion of the piston. This entire system is immersed in refrigeration oil, which lubricates the rubbing parts and removes some of the heat.
The key element is piston group, consisting of a cylinder, piston and valve system. When the piston moves downward, a vacuum is created in the cylinder, and freon gas is drawn from the evaporator through the suction valve. When moving upward, the gas is compressed and pushed through the discharge valve into the condenser.
The electric motor, located in the upper or lower part (depending on the model), has starting and operating windings. To start, it is used starting relay, which briefly supplies current to the starting winding, creating torque. After gaining speed, the relay turns off the starting circuit, and the engine operates on the working winding.
⚠️ Attention: Inside the housing there may be ammonia or propane as a refrigerant mixed with oil. When the casing is opened, these gases escape. Work should be carried out in a well-ventilated area, away from open fire.
To cool the motor, the coolant itself is used, which, passing through the casing, washes the heated windings. This is why the housing of a running compressor can heat up to high temperatures. The tightness of the weld ensures that there are no leaks and no moisture gets into the system.
Necessary tools for opening the case
Disassembling a sealed casing is an operation that requires mechanical action on the metal. A standard DIY kit will not help here, since the body is welded in a circle. To access the insides, you will need a specialized tool that allows you to make a neat cut or cut.
The main tool is an angle grinder (grinder) with a thin cutting disc for metal or a specialized cutter for compressors. Using a hacksaw for metal is possible, but extremely labor-intensive and often leads to deformation of the casing, which will complicate subsequent assembly even for demonstration purposes.
You will also need:
- 🛠️ A set of wrenches and screwdrivers for dismantling the attachment equipment.
- 🔨 Hammer and chisel (for carefully chipping off the weld if a saw is not used).
- 🧤 Safety glasses and gloves to protect against metal shavings.
- 🔌 Multimeter for testing the windings after opening.
Don't forget to prepare a container for draining the oil. It may be black and have a burning smell if the compressor was overheated. To secure the housing when cutting, it is convenient to use a vice or reliable clamps so that the housing does not rotate.
⚠️ Attention: When using an angle grinder, sparks can ignite residual oil or refrigerant vapor. Before cutting, thoroughly blow out the internal pipes with compressed air or simply make sure that the compressor has not been running for a long time.
Technology for disassembling a sealed casing
The first step is to remove all external elements: the start relay, capacitor and copper tubes. The tubes are cut with wire cutters at a distance of 10-15 cm from the body in order to be able to plug the holes later or connect pressure gauges. Drainage hole in the lower part of the casing (if any) it also opens to drain the oil.
Then follows the cutting process. A weld runs along the equator of the body. It is necessary to make a cut around the entire perimeter, being careful not to damage the internal windings and stator. The cutting depth is controlled visually and by touch - as soon as the disc stops meeting metal resistance, but does not yet touch the internal parts, the saw is stopped.
After a complete cut, the top cover (cap) is removed. In some models it may be tight due to oil residue or corrosion. Light blows with a wooden mallet around the perimeter will help separate the halves. Inside you will see a massive stator with windings and a rotor mounted on a shaft.
☑️ Procedure for opening the compressor
It is important not to damage the copper oil supply tubes, which often go inside the casing. If you plan to further use the unit (which is unlikely if opened), vacuuming and sealing again is required, but at home this is almost impossible to do efficiently.
Detailed analysis of the internal structure
After removing the cover, you will see a classic picture of an electromechanical device. The central place is occupied by crank mechanism. At the end of the rotor shaft, a connecting rod is eccentrically fixed, which with its lower end covers the piston pin. When the shaft rotates, the connecting rod causes the piston to move up and down inside the cylinder.
The cylinder is made of high-strength steel, and the piston has minimal clearance with its walls to ensure compression. At the end of the cylinder there is a valve plate - a thin metal plate with two holes. One hole works for suction, the other for discharge. The valves are thin elastic petals that open under gas pressure.
Below is a table of the main components that you will find inside:
| Component | Material | Function |
|---|---|---|
| Stator | Electrical steel, copper | Creation of magnetic field |
| Rotor | Steel, aluminum | Shaft rotation engine |
| Crankshaft | Steel | Conversion of rotation into intake |
| Piston | Cast iron or steel | Compression refrigerant |
The oil intake pipe goes down to the bottom of the casing. A filter mesh is often installed at its end, which can become clogged with decay products of oil and varnish. It is the clogging of this mesh or tube that often leads to noisy operation or failure of the compressor.
Why does the piston not fall?
The piston does not fall out of the cylinder even when the compressor is inverted due to the precise fit and oil film, but with severe wear of the cylinder-piston group, play may be observed leading to knocks.
Diagnostics of faults when the unit is disassembled
Open access to the insides allows you to identify the causes of failure that could not be diagnosed from the outside. A common problem is scuffing on the cylinder bore or piston skirt. This happens when working without oil or when there is a lack of oil. The metal surface becomes rough, which leads to a wedge.
If the motor windings are blackened and have a burning smell, it means that an interturn short circuit or a breakdown to the housing has occurred. You can check the integrity of the windings with a multimeter in resistance measurement mode. The normal resistance of the working winding is usually 10-30 Ohms, the starting winding is 30-60 Ohms (values depend on the model Atlant, Danfoss or others).
Pay special attention to the valve plate. If the valve petals are broken or deformed, the compressor will operate but not produce the required pressure. Freon will simply be transferred from a high pressure zone to a low pressure zone without effective compression. This is a common reason why the refrigerator freezes weakly or does not freeze at all.
⚠️ Attention: If you find metal shavings in the oil or at the bottom of the casing, this is a sign of destruction of the bearings or piston group. Such a compressor requires a complete replacement, since chips will inevitably enter the system and clog the capillary tube.
Also check the condition of the starting winding. If it is broken, the engine will hum, but will not start until the thermal relay is activated. Visually, a break may not be noticed, so a continuity test is required.
Possibility of repair and reassembly
It should be understood that that hermetic compressors are designed as maintenance-free units. Factory welding ensures absolute tightness, which cannot be replicated in a garage environment. Attempts to weld the casing by electric welding often lead to burning of thin metal or damage to the internal insulators.
There are special repair kits with bolted connections of the casing halves and rubber seals, but they are rare and are not suitable for all models. Even with successful mechanical assembly and vacuuming, the quality of such repairs is inferior to the factory one. The risk of freon leakage or moisture ingress remains high.
If the purpose of disassembly was to repair the piston group (replacing rings, grinding the cylinder), then in domestic conditions this is practically impossible due to the lack of precision equipment. Replacing the compressor to a new analogue is the only correct technical solution for restoring the refrigerator.
However, a disassembled compressor is an excellent learning material. You can bolt it back together (by drilling holes in the flange) to demonstrate the principle of operation or use it as a vacuum pump (with certain modifications).
In conclusion, knowledge of the internal structure helps to correctly diagnose a breakdown without resorting to replacing expensive components. But remember that the integrity of the circuit is the main condition for the operation of the refrigerator.
Is it possible to change the oil in a refrigerator compressor?
Theoretically it is possible, but in practice it is difficult. The old oil must be completely removed, and new oil must be poured through the process pipe under vacuum. The usual “drained-filled” replacement is ineffective, since residues of old oil and decay products remain inside.
Why does the compressor get very hot after disassembly?
When operating in an open state (without freon), the compressor heats up very quickly, since the gas does not cool the windings and piston group. Prolonged operation "in air" without load can lead to overheating and jamming.
What type of oil is used in refrigeration compressors?
Special synthetic oils are used (polyester POE, polyvinyl chloride PVC) or mineral, depending on the type of refrigerant (R134a, R600a). Regular motor oil cannot be used - it will freeze or react with freon.
What to do if the compressor hums after assembly?
A hum may indicate improper assembly of the crank mechanism, piston misalignment or damage to the valves. It is also possible that chips or dirt got inside. Repeated troubleshooting is required.