When you hear a characteristic hum coming from the back wall of the refrigerator, you hear the heart of the entire cooling system working. Many take this sound for granted, without thinking about the complex processes hidden under the metal casing. It is there, in a sealed housing, that the refrigerant is compressed, forcing it to circulate through the tubes and remove heat from the products.
Understanding this what is in the refrigerator compressoris necessary not only for general development, but also for the correct diagnosis of breakdowns. The internal structure of the unit is a complex engineering system, where each element performs a critical function. Malfunction of even one small part can lead to a complete stop of the entire cooling system.
In this article we will look “under the hood” of this device, analyze the design of the piston group, the valve system and the role of engine oil. You will find out why the case is sealed tightly and what physical laws govern the operation of your of a refrigeration unit. This knowledge will help you distinguish normal operating noise from signs of impending failure.
Sealed housing: why you can’t look inside
The first thing a person who decides to study the design of a compressor is faced with is the inability to simply remove the cover. The body is a welded steel capsule, often called a "pot". This design was not chosen by chance, but was dictated by the requirements for the safety and efficiency of freon.
Excess pressure is created inside this casing, and any depressurization at home will lead to an instant release of the refrigerant into the atmosphere. Moreover, oil gets inside the housing, which is in a suspended state along with freon vapor. Open compressor in the air it will instantly lose its properties, and moisture will get inside the system, which is detrimental to the refrigerator.
⚠️ Attention: It is strictly forbidden to open the sealed compressor casing without specialized equipment and skills rations. This will not only disable the equipment, but can also be dangerous due to the high pressure and flammability of some types of refrigerants.
However, knowledge of the design is necessary. Inside the casing there are two main components: an electric motor and a mechanical compressor part. They are located on a single base and suspended on springs to dampen vibrations. If you hear a knocking sound or strong vibration, it often means that suspension springs have worn out or burst, and the metal frame is starting to bang against the casing.
Electric motor: the source of energy for the system
The basis of the lower part of the unit is an asynchronous electric motor. It operates from a standard network, but its design is adapted to work in an environment of freon and oil. Stator the engine is fixedly mounted on the housing, and Rotor is placed directly on the compressor shaft. This direct transmission of torque eliminates the need for belts or gears.
The motor windings are immersed in an oil mixture, which performs two functions: it lubricates the rubbing parts and removes heat from the windings. This is why the compressor heats up during operation - it removes the heat obtained from gas compression and the operation of electric current. If the oil loses its properties or its level drops, the engine can burn out in a matter of minutes.
To start the engine, a starting relay is used, which is located outside the housing, but is electrically connected to the windings inside. It briefly supplies increased current to the starting winding, creating the necessary torque. After a set of revolutions, the relay turns off the starting circuit, and the engine runs on the main winding.
Why is the engine inside and not outside?
Placing the electric motor inside a sealed housing eliminates the risk of freon leakage through the shaft seals. In open compressors (used in car air conditioners), the shaft seal is a weak point. In the refrigerator, the shaft does not come out; it is directly connected to the rotor, which makes the system absolutely sealed and durable.
Crank mechanism and piston group
The heart of the mechanical part is the crank mechanism, which converts the rotational movement of the shaft into the translational movement of the piston. The shaft has an eccentric (crank) onto which the lower head of the connecting rod is placed. When the shaft rotates, the connecting rod makes oscillatory movements, pushing the piston up and down.
The piston itself is made of light alloy and has minimal clearance relative to the cylinder walls. Modern models use pistons with minimal friction, often with Teflon coating or a special notch to retain the oil film. The manufacturing precision of these parts is extremely high, since any misalignment leads to jamming.
On the top of the cylinder there is a head with a valve plate. This is where the process of gas suction and injection takes place. When the piston moves down, a vacuum is created and gas from the evaporator enters the cylinder through the suction pipe. When moving upward, the gas is compressed and pushed through the discharge valve into the condenser.
| Element | Material | Function | Typical fault |
|---|---|---|---|
| Shaft cranked | Steel | Rotation transmission | Bearing wear, scuffing |
| Connecting rod | Aluminum alloy | Conversion movement | Breaking of bushing holes |
| Piston | Cast Iron/Alloy | Refrigerant compression | Ring jamming, scuffing |
| Valve plate | Steel | Flow distribution | Valve petals burst |
Valve system: flow adjustment
The thinnest and most sensitive The mechanical element is the valve assembly. It is a thin metal plate with slots (petals) that act as check valves. These petals open under the influence of pressure differences and close due to their own elasticity.
The suction valve allows gas only into the cylinder, and the discharge valve only from the cylinder into the system. If the valve petal breaks or loses elasticity, the compressor stops producing the necessary pressure. In this case, the refrigerator will hum, but will not produce cold, since the freon will simply be distilled back and forth without compression.
The valve material must have high strength (fatigue strength), since they make thousands of vibrations per minute. The use of low-quality spare parts leads to rapid failure. In some models, instead of plate valves, ring or disc valves are used, but the principle of their operation remains the same.
The role of oil and the lubrication system
There is a special one inside the compressor refrigeration oil. It differs from automobile or machine in composition and properties. Its main feature is the ability to dissolve in freon and circulate with it throughout the entire system, without precipitating or freezing at low temperatures.
Lubrication of rubbing parts (shaft, connecting rod, piston) occurs by splashing. At the end of the shaft there is often a special vane or capillary, which, when rotated, captures oil from the crankcase and sprays it or delivers it under pressure to the bearings. The oil level is critically important: if there is a deficiency, dry friction occurs; if there is too much, the efficiency of heat transfer in the condenser decreases.
⚠️ Attention: Never mix different types of oils (mineral and synthetic). Different types of freon (R134a, R600a, R12) use different oils. Changing the oil without flushing the system is a serious mistake leading to the formation of acids and resins.
Oil also acts as a seal between the piston and the cylinder walls, preventing gas breakthrough. In addition, it carries away heat from rubbing surfaces. If you see that when cut, a black, thick liquid with a burning smell flows out of the compressor tube, this means that engine oil it has burned and turned into acid, which corrodes the insulation of the windings.
Diagnostics of internal problems by external ones signs
Although we do not see what is happening inside, indirect signs allow us to determine the state of the nodes. For example, if the compressor starts with a strong hum and clicking noise and then stalls, the piston is most likely stuck or the winding is burned out. If it works, but does not cool, the problem is in the valves or lack of freon.
Vibration of the housing may indicate a break in the motor suspension springs inside the casing. In this case, the motor hits the walls, creating a lot of noise. Sometimes gently rocking the refrigerator to get the motor into place helps, but this is a temporary measure. It is also important to check the temperature of the case: it should be hot (50-80°C), but not red-hot.
☑️ Symptoms of a compressor malfunction
There is a technique for “testing” the windings with a multimeter, which allows you to assess the integrity of the electrical parts without opening. The resistance between the contacts must be within certain limits (usually from 10 to 30 Ohms for the working winding and more for the starting winding). If the resistance is zero - a short circuit, if infinity - an open circuit.
Frequently asked questions about the internal structure
Is it possible to change the oil in the compressor yourself?
Theoretically, it is possible by cutting off the tubes and pouring out the old oil, but in practice this is difficult. It is necessary to know exactly the type of oil, its quantity and brand. In addition, simply changing the oil will not help if there are wear products inside (metal shavings) that need to be washed out with special solvents under pressure. At home, it is easier and cheaper to replace the entire unit.
Why is the compressor hot to the touch?
This is normal. The compressor compresses the gas, which, according to the laws of physics, is accompanied by an increase in temperature. In addition, the electric motor windings heat up from the passage of current. The normal temperature of the housing of a working compressor can reach 70-90 degrees Celsius. It is dangerous if it heats up to temperatures at which the insulation of the wires melts or the paint chars.
What does a knock inside the compressor mean when starting?
A single knock or click when starting can be the norm (relay operation or water hammer). But if the knock is repeated, metallic and accompanied by vibration, this indicates broken shaft bearings, wear of the piston group or a broken valve. Such a unit requires replacement.
How long does the compressor last?
The average service life of a modern compressor is 10-15 years, provided proper operation and stable voltage in the network. However, frequent voltage fluctuations, overheating (due to dust on the condenser at the back of the refrigerator) and improper defrosting can reduce this period to 5-7 years.