The question of what exactly a compressor is in a domestic refrigerator often confuses those who are not familiar with engineering terminology. At first glance, it is just a buzzing black “barrel” at the back of the unit, but complex mechanics are hidden inside it. Many call it a motor, and there is some truth in this, but technically this definition is incomplete and simplified.
In fact, compressor it is not just an electric motor, but a complex unit that combines a power drive and a pumping system. It is this bundle that circulates the refrigerant, turning gas into liquid and creating the necessary pressure to cool the chambers. Understanding this difference is critically important when diagnosing breakdowns, since replacing one unit does not always solve the problem.
In this article we will analyze in detail the internal structure of this unit, consider its role in the overall operating cycle of the refrigeration machine and answer the question why it cannot be considered a regular motor. You will learn what types of mechanisms exist and how to determine what exactly has failed - the electrical part or the mechanical one.
The fundamental difference between a motor and a compressor
To understand the essence of the device, it is necessary to clearly separate the concepts of “engine” and “compressor”. An electric motor is a device that converts electrical energy into mechanical rotation of a shaft. It creates torque, but by itself is not capable of compressing gases or pumping liquids under high pressure.
A compressor is volumetric machine, whose main task is to compress a gaseous substance and move it along a closed circuit. In household refrigerators, these two devices are most often combined into a single sealed housing. Inside this casing, the electric motor is directly connected to the crank mechanism, which performs the function of a pump.
Thus, when you hear a hum from behind the refrigerator, you hear the work of the connection: electric motor + compressor group. If the motor winding burns out, the compressor will not start. If the piston group or valves jam, the motor may hum, but no useful work will be done to compress the freon. This is a key point for technicians during diagnostics.
⚠️ Attention: An attempt to start the compressor without connecting to the pipe system (in the open air) is strictly prohibited. In some models, the intake air flow is used to cool the motor windings, and running “idle” can lead to overheating and melting of the insulation in a matter of minutes.
The separation of functions within one housing allows you to save space and reduce noise levels, since vibrations are damped by the internal design. However, this also makes repairs difficult: if a mechanical part breaks down, it is often necessary to replace the entire assembly, since opening the sealed casing at home is impossible without losing the seal.
Internal structure: what is inside the casing
It is impossible to look inside a standard hermetic compressor without sawing it, but the scheme of its operation is well known to engineers. The basis of the design is the stator and rotor of the electric motor, which are rigidly mounted on springs or rubber shock absorbers inside a steel housing. This is done in order to minimize vibrations transmitted to the refrigerator body.
A crankshaft is attached directly to the rotor shaft, which drives the piston. When the shaft rotates, the piston makes reciprocating movements in the cylinder. This process is reminiscent of the operation of an internal combustion engine, but with one difference: there is no ignition of the fuel, but only compression of the refrigerant.
In the upper part of the cylinder there is a system valves (suction and discharge). They operate automatically, opening and closing depending on the pressure in the cylinder. It is these thin plates that often become the cause of breakdown: when they are deformed or broken, the compressor stops creating the necessary pressure, and the refrigerator stops freezing, although the motor hums properly.
Why are compressors made hermetically sealed?
A sealed casing prevents freon leakage and protects internal mechanisms against moisture and dust. In addition, refrigerant vapor inside the housing is used to cool the windings of the electric motor, which increases the efficiency and durability of the unit.
Also inside the housing there is oil, which is necessary to lubricate the rubbing parts: bearings, piston and cylinder. The oil is not consumed during normal operation, but circulates along with the refrigerant, returning back to the compressor crankcase. The level and condition of the oil is an important indicator of the health of the unit.
Types of compressors: from classic to inverter
Technology does not stand still, and modern refrigerators can be equipped with various types of compressors. Understanding the difference between them will help you choose more reliable equipment or correctly estimate the cost of repairs.
- 🔹 Piston compressors - the classic option, where gas compression occurs due to the movement of the piston. They are reliable, repairable (partially), but create noticeable noise and vibration during startup and operation.
- 🔹 Rotary compressors - here compression occurs due to the rotation of the rotor in the stator. They are smaller, quieter and have fewer moving parts, which theoretically increases their reliability, but they are more sensitive to build quality.
- 🔹 Inverter compressors are the pinnacle of evolution. Unlike conventional ones, which operate in the “on-off” mode, the inverter motor does not stop completely, but only changes the rotation speed. This ensures constant temperature and significant energy savings.
Inverter models, such as Digital Inverter from Samsung or Linear Inverter from LG, operate almost silently. However, their electronics are more complex and they are sensitive to power surges. A conventional piston compressor is easier to “forgive” current surges, although its starting currents are higher.
The choice between types of compressors often becomes a choice between the initial cost of the refrigerator and its future energy efficiency. Inverter models are more expensive, but last longer and consume less electricity, which in the long run pays for the difference in price.
Principle of operation: how cold is created
To understand why a compressor is needed, imagine the refrigeration circuit as a closed system of pipes through which refrigerant (freon) circulates. The compressor here acts as a “heart” that pumps “blood” (gas) through the “veins” of the system.
The process begins with the compressor sucking gaseous freon of low pressure and temperature from the evaporator (located inside the refrigerator). It then compresses this gas, dramatically increasing its pressure and temperature. In this state, hot gas under high pressure is sent to the condenser (the grill at the back of the refrigerator), where it cools and turns into liquid.
Next, the liquid refrigerant passes through capillary tube or a choke, where the pressure drops sharply. Entering the evaporator, the liquid boils at a low temperature, actively absorbing heat from the refrigerator chambers. Having turned back into gas, freon is again sucked in by the compressor, and the cycle repeats.
| Cycle stage | Freon state | Compressor action | Location |
|---|---|---|---|
| Suction | Low pressure gas | Gas intake from the system | Inlet tube |
| Compression | Gas of high pressure and temperature | Mechanical compression by piston | Inside the cylinder |
| Discharge | Hot gas | Extrusion to the condenser | Output tube |
| Waiting | Liquid | Rest (in conventional models) | Condenser/Evaporator |
Without a compressor, this cycle would be impossible: gas would not be able to spontaneously move from a low-pressure zone to a high-pressure zone. It is the work of the compressor that sets the rhythm for the entire cooling process.
Fault diagnosis: motor or mechanics?
When the refrigerator stops cooling, the first thing to check is the compressor. But how can you figure out what exactly is broken? There are several characteristic signs that allow you to differentiate an electrical malfunction of the motor from a mechanical breakdown of the pump part.
If the compressor is silent and does not make any sounds, but the light inside the refrigerator is on and there is voltage in the socket, the problem may be in the start relay, thermostat, or a broken motor winding. In this case, the motor does not receive a start command or cannot turn the shaft due to an electrical defect.
If you hear a characteristic hum that lasts several seconds, and then there is a click and silence, this often indicates jamming of the mechanical part or failure of the starting winding. The motor tries to start the compressor, but the piston is jammed, the current increases, and the thermal relay opens the circuit to save the windings from combustion.
☑️ Primary diagnostics of the compressor
⚠️ Attention: If the compressor runs continuously without turning off, and the refrigerator does not freeze well, this may indicate a freon leak or loss of compression (valve wear). Long-term operation in this mode will lead to overheating and combustion of the motor.
You should also pay attention to the temperature of the case. If the compressor casing is too hot to touch, this is a warning sign. Normal operating temperature can be high (60-80°C), but should not cause a burn upon short-term touch.
Maintainability and replacement of the unit
The issue of compressor repair often depends on economic feasibility. Theoretically, you can replace the starting relay, capacitor, or even rewind the motor windings. However, if the problem lies in the mechanical part (scuffing in the cylinder, broken valves), repairs in a service center become impossible due to the need to weld the casing and evacuate the system.
In 90% of cases, when a compressor group breaks down, the technicians offer replacement of the unit the whole thing. This is due to the fact that the cost of re-pressing work (opening and sealing) often exceeds the cost of a new compressor, and the warranty for such repairs is minimal.
When replacing, it is important to select an analogue with identical characteristics: power, refrigerant (R134a, R600a), type of oil and mounting geometry. Installing an unsuitable compressor will either result in insufficient cooling or rapid failure of the new part.
Modern inverter compressors are often replaced together with an electronic control unit, since they are a single system. The cost of such spare parts is high, which makes prevention and careful operation even more relevant.
Frequently asked questions (FAQ)
Is it possible to use a regular car compressor to repair a refrigerator?
No, it is impossible. Automotive compressors are not designed to work with refrigerants, do not have the necessary tightness and cannot provide the required pressure and performance for the refrigeration cycle. In addition, they are not compatible with refrigeration oils.
Why does the compressor get very hot during operation?
Heating to 70-90 degrees Celsius is the norm for a working compressor, since heat is released when the gas is compressed. However, if it becomes red hot or has a burning smell, this is a sign of a malfunction: problems with ventilation, a freon leak, or an interturn short circuit in the motor.
How long does a compressor last in a refrigerator on average?
The service life of modern compressors is from 10 to 20 years. Inverter models, due to the absence of constant starting loads, theoretically last longer, but their service life also depends on the quality of the voltage in the network and operating conditions (for example, frequency of defrosting).
Is it dangerous to open the compressor yourself?
Yes, it is dangerous. Firstly, pressure may remain inside. Secondly, sawing the housing can create sparks that ignite oil vapor or residual refrigerant. In addition, moisture will get inside, which will make the unit unsuitable for further operation in the cooling system.
Will a compressor replace a freezer in a homemade project?
A compressor is just a pump. To create a freezer (for example, for a moonshine still or an air conditioner), you will also need a condenser, an evaporator, a capillary tube, a filter drier and the right refrigerant. Without creating a closed loop, the compressor will simply blow air.