The compressor is often called the heart of the refrigeration unit, and this comparison perfectly describes its role in the system. It is this unit that is responsible for the circulation of the refrigerant, creating the necessary pressure for the transition of freon from a gaseous state to a liquid state and back. Without this mechanism working properly, the refrigerator compartment turns into an ordinary cabinet, unable to keep food fresh. However, few owners of household appliances think about what complex processes occur inside this black metal “barrel” while it hums in the kitchen.
Understanding the internal structure is necessary not only for repair engineers, but also for ordinary users who want to extend the life of the equipment. Knowing how the compressor workshelps to correctly diagnose problems based on the nature of the noise or lack of startup. Inside the sealed housing are hidden mechanics that operate under high pressure and extreme temperatures. Let's look inside this device to understand the principles of its operation and possible causes of breakdowns.
Sealed casing: protection and insulation
The outer shell of the compressor is a welded sealed casing made of durable steel. This design is not accidental: it is designed to prevent any leakage of refrigerant and oil into the environment. A pressure is created inside the housing that can significantly exceed atmospheric pressure, so the integrity of the seams and welded joints is critical for operational safety. Sealed housing also acts as a noise muffler, hiding vibrations of operating mechanisms.
Despite the external solidity, the housing is equipped with several pipes. Tubes for suction and discharge of refrigerant pass through them, as well as electrical leads for connecting the motor windings. These terminals are insulated with special ceramic or plastic bushings that can withstand high voltage and temperature. Any damage to these insulators can lead to a short circuit or breakdown of current to the housing, which is dangerous for humans.
A special atmosphere reigns inside the casing, saturated with oil and freon vapors. This is necessary to lubricate rubbing parts and effectively dissipate heat. Internal temperature an operating unit can reach high values, so it is important that the housing effectively dissipates heat. That is why the outer surface of the compressor becomes very hot during operation.
⚠️ Attention: It is strictly forbidden to open the welded compressor housing at home without special equipment. High pressure may remain inside even after a long period of inactivity, and refrigerant vapors upon contact with an open flame can form toxic compounds.
Electric motor: energy source
The main driving element of the system is electric motorlocated at the bottom body parts. Most household refrigerators use squirrel-cage asynchronous motors. They are distinguished by their simplicity of design and high reliability, which is critical for equipment that operates around the clock for years. The engine is rigidly mounted on a frame, which, in turn, is suspended on springs inside the casing to dampen vibrations.
The motor stator consists of a set of metal plates on which copper windings are wound. Usually there are two of them: working and starting. The working winding provides the main rotation, and the starting winding helps overcome inertia at the moment of start. Copper wire is covered with special heat-resistant insulation that can withstand heating up to 120-130 degrees Celsius. If the insulation dries out or melts, an interturn short circuit occurs and the engine burns out.
The engine rotor is pressed onto a shaft, which is a continuation of the crankshaft of the compressor part. This design allows direct transmission of torque without the use of belts or gears. The absence of additional transmission mechanisms reduces energy losses and reduces the number of parts subject to wear. The reliability of this connection directly affects the energy consumption of the refrigerator.
Crank mechanism and piston group
The heart of the mechanical part is crank mechanism, which converts the rotational movement of the shaft into the translational movement of the piston. The shaft, which is a continuation of the engine rotor, has an eccentric (crank) onto which a connecting rod is placed. When the shaft rotates, the connecting rod begins to make oscillatory movements, pushing the piston up and down.
The piston moves inside the cylinder, creating zones of rarefaction and compression. Modern refrigerators most often use pistons made of special aluminum alloys or steel with minimal tolerances. The gap between the piston and the cylinder walls is microscopic, which requires perfect lubrication. If the oil thickens or its level drops, metal scuffing occurs and the unit quickly fails.
At the end of the cylinder there is a valve plate - a thin metal part with holes closed by valve reeds. These valves work like automatic dampers: they open under gas pressure and close under their own weight or elasticity. It is the breakdown of the reed valve that is one of the most common causes of loss of performance compressor. When the valve breaks or is deformed, the compressor hums, but does not pump freon, and the refrigerator stops freezing.
Why does the compressor hum but does not start?
If you hear a hum that ends after a few seconds with a click, this means that the engine is trying to start, but it does not have enough torque or pressure. Most often, the problem lies in a jammed piston, a faulty start relay, or an interturn short circuit in the winding. Prolonged humming without starting can lead to burnout of the windings.
Lubricating system and refrigerant
Inside the sealed compressor housing there is not only air, but also special refrigeration oil. It is necessary to lubricate rubbing pairs: piston and cylinder, shaft bearings, parts of the crank mechanism. The oil must have the following properties: low pour point, chemical inertness towards freon and metal, as well as good fluidity.
Lubrication is carried out by splashing. At the lower end of the shaft there is often a scoop (oil lifter), which, when rotated, captures oil and feeds it up the shaft channel. From there, the oil is sprayed onto the bearings and cylinder walls. After performing its function, the oil flows back to the lower part of the housing (crankcase), where it mixes with freon vapor. The mixture of oil and refrigerant circulates throughout the entire circuit of the refrigeration system.
It is important to understand that the type of oil depends on the type of refrigerant used. For old freons (R12), mineral oils were used, and for modern ones (R134a, R600a), synthetic ones (polyester or polyvinyl ether) are used. Mixing different types of oils is strictly prohibited, as this can lead to the formation of acids that destroy the insulation of the windings and metal parts. When replacing a compressor, you should always use the oil recommended by the manufacturer.
Starting and protective relay: start control
Although these parts are often located on the outside of the housing, they are an integral part of the compressor control system. Starting relay connects the starting winding of the engine only at the moment of start, when maximum force is required to break the piston from its place. As soon as the shaft picks up speed, the centrifugal mechanism or a change in current opens the starting winding circuit.
Thermal protective relay (thermal relay) is used for emergency shutdown of the engine in case of overload or overheating. Inside it is a bimetallic plate that bends when the temperature rises and opens the contacts. This saves the windings from burning out in the event of a piston jamming or power surges in the network. After cooling, the relay usually closes its contacts automatically, attempting to start the compressor again.
In modern inverter models, traditional relays are replaced by electronic control units that smoothly regulate the engine speed. This avoids inrush currents and reduces noise levels. However, in classic linear compressors, mechanical or electromagnetic relays remain the standard for reliability and low cost of repair.
☑️ Signs of a compressor malfunction
Table: Main components and their functions
To systematize the information, let's look at the main components compressor in the summary table. This will help you quickly identify parts when studying diagrams or fault descriptions.
| Component | Material | Main function | Typical fault |
|---|---|---|---|
| Housing | Steel | Sealing and sound insulation | Corrosion, violation of seam tightness |
| Stator/Rotor | Copper, electrical steel | Creation of torque | Interturn short circuit, broken winding |
| Piston | Aluminium, steel | Refrigerant compression | Scuffing, ring wear, jamming |
| Valve plate | Elastic steel | Gas flow adjustment | Breakage of reeds, loss of elasticity |
| Oil | Synthetics/Mineral | Lubrication and cooling | Oxidation, loss of viscosity, mixing |
Diagnostics and typical problems
Understanding that what's inside the compressorallows the master to make a diagnosis based on indirect signs. For example, if the compressor runs continuously without turning off, and the chamber is not cold enough, this may indicate wear on the piston group or a freon leak. The engine tries to compensate for the lack of pressure by working towards wear.
A loud metallic knock during startup often indicates broken bearings or severe wear of the connecting rod group. If you hear a quiet hum that turns into a click and the unit goes silent, the problem is most likely in the start relay or the piston wedge. In the latter case, the motor shaft cannot turn, and the thermal relay emergency cuts off the power.
Therefore, if the mechanical or electrical part of the “filling” breaks down, the compressor usually must be completely replaced with a new unit.
⚠️ Attention: If you smell burning or see sparking in the compressor area, immediately unplug the refrigerator. Operating faulty electrical equipment may result in a fire. Do not attempt to repair the live electrical part.
Is it possible to repair a refrigerator compressor yourself?
Theoretically, you can replace the start relay or thermal protection yourself if you have the skills to work with electrical equipment. However, repairing the internal mechanical parts (piston, valves) or rewinding the engine at home is impossible. This requires opening the case, which breaks the seal, and subsequent professional sealing, vacuuming and refilling with freon. In 99% of cases, if there is an internal breakdown, the entire compressor is replaced.
Why does the compressor get very hot?
Heating the housing to 70-90 degrees Celsius is the norm for a working compressor. However, if it becomes too hot to touch, it may indicate a problem: insufficient coolant, a clogged capillary tube, a faulty thermostat, or worn-out motor. Also, the cause may be poor ventilation around the refrigerator.
How long does the compressor last in the refrigerator?
The average service life of a modern compressor is 10-15 years, provided proper operation. Inverter models can operate longer due to the absence of constant starting loads. The service life strongly depends on the stability of the voltage in the network, the quality of installation and the timeliness of defrosting (for No Frost systems this is less relevant, but important for the overall load).
Is it dangerous to touch the copper tubes of the compressor?
When the refrigerator is running, one tube (discharge) can be very hot, and the other (suction) can be cold or even covered frost. Touching a hot tube can lead to burns, and prolonged contact with a very cold tube can lead to frostbite. In addition, copper tubes are soft, and if handled carelessly, they can easily be damaged, which will lead to freon leakage.