Refrigerator compressor working principle, wiring diagram, structure

The core component of the refrigerator is the compressor. If a refrigerator is not equipped with a compressor of good quality and technology, it cannot be a good refrigerator. At present, there are many products on the market that are advertised by the use of high-quality compressors, but it is difficult for us as customers to distinguish. The following will introduce the working principle of refrigerator compressors, wiring diagrams and several common compressors. Hope to bring some help for you on how to choose the refrigerator compressor.

The structure of household refrigerator products is not complicated. It is generally composed of the compressor, condenser, filter drier, capillary tube, evaporator and other important components connected into a loop. As one of the most complex mechanical components, the compressor is naturally in the most important position, and it is also the most technical component in the refrigerator. Generally, the compressor has a great influence on factors such as refrigeration efficiency and noise.

How Refrigerator Compressors Work

Refrigeration cycle process diagram of refrigerator compressor

Figure 1: Refrigeration cycle process diagram of refrigerator compressor.



The compressor can be said to be the heart of refrigerator refrigeration. Without it, the refrigeration system of the entire refrigerator will not work properly. Its working principle can be divided into the following 5 steps:

1.When the refrigerator is working, it mainly sucks the refrigerant through the compressor. After the refrigerant is sucked into the compressor, it will become a high temperature and high pressure gaseous refrigerant after being compressed by the compressor, and then be sent to the condenser through the pipeline.

2.In the condenser, the refrigerant will begin to release heat, and after condensation, the high-temperature and high-pressure gaseous refrigerant will become a low-temperature and high-pressure liquid refrigerant.

3.After the refrigerant is condensed, it will enter the capillary tube (or expansion valve), and through the throttling and decompression, the pressure of the refrigerant will decrease, and finally enter the evaporator.

4.The space in the evaporator is much wider than in the capillary tube. After entering the evaporator, the low-temperature and low-pressure liquid refrigerant will absorb heat and evaporate rapidly, and eventually become an isothermal and isobaric gaseous refrigerant.

5.After that, the gaseous refrigerant will be sucked and compressed by the compressor again to continue the refrigeration cycle. As the evaporation of refrigerant absorbs heat, the temperature in the refrigerator also decreases, and finally the refrigeration is achieved. The compressor powers the refrigeration cycle.



Simple diagram of the compressor working process including air intake, air compressing, air exhaust

Figure 2: Simple diagram of the compressor working process.

Refrigerator Compressor Wiring Diagram

There are 3 terminals on the top of the compressor, namely S, M, C, where S is the starting winding, M is the running winding, and C is the common terminal.
The resistance value of the running and starting terminals (MS) is the largest;
The resistance value of starting and common terminals (SC) is medium;
The resistance value of running and common terminals(MC) is the smallest.



Refrigerator compressor wiring diagram including two types, RSIR and CSR

Figure 3: Refrigerator compressor wiring diagram.

Compressor Quality Measurement

1.Use a multimeter to measure its resistance value. It is normal that the resistance value between SC and MC is equal to the resistance value between MS. For example, the resistance between SC is 5 ohms and the resistance between MC is 3.5 ohm, then the resistance value between MS is 8.5 ohms (allowing a little deviation, not too large). If the resistance offset is too large, or there is no resistance between the three, then the compressor must be broken!

2. Sometimes, it is normal to measure with a multimeter, but the internal short circuit of the compressor cannot be measured. The easiest way is to use a multimeter to measure whether it is powered on. If it does not start after powering on, you can replace a starting capacitor (50UF). If it still does not start, then the compressor is broken!

Structure of Seven Types of Compressors

1. Screw Compressor

Structure diagram of oil-injected screw refrigeration compressor including two screw rotors

Figure 4: Structure diagram of oil-injected screw refrigeration compressor.



The main components of a screw compressor include: a pair of rotors, a body, a bearing, a synchronous gear (sometimes including a speed-increasing gear), and sealing components.

Working principle: Two screw rotors that rotate in opposite directions according to a certain transmission ratio and mesh with each other are arranged in parallel in the "∞"-shaped cylinder. Usually, one rotor is called the male rotor (also called the driver rotor); the other is called the female rotor (also called the driven rotor).

The helical bodies on the female and male rotors are called female screw and male screw, respectively. Generally, the male rotor (or through the speed-increasing gear set) is connected with the prime mover, and gets power from it; the male rotor (or through the synchronous gear set) drives the female rotor to rotate.

According to different operating modes, screw compressors can be divided into two categories: oil-free compressors and oil-injected compressors.
According to the number of screws, screw compressors are divided into single screw compressors and twin screw compressors.



structure diagram of single screw compressor including a screw rotor and two symmetrically arranged flat star gears

Figure 5: Structure diagram of a single screw compressor.

2. Sliding Vane Compressor

Structure of sliding vane compressor

Figure 6: Structure of sliding vane compressor.



The main parts of the sliding vane compressor are composed of three parts (as shown in the figure below): the body (also known as the cylinder), the rotor 3 and the sliding vane 5.

Working principle: The rotor of the sliding vane compressor is eccentrically arranged in the cylinder, and there are several longitudinal grooves on the rotor, and sliding vanes that can slide freely in the radial direction are installed in the grooves. Since the rotor is eccentrically arranged in the cylinder, a crescent-shaped space is formed between the inner wall of the cylinder and the outer surface of the rotor.

When the rotor rotates, the sliding vane is thrown out of the groove by centrifugal force, and its end is closely attached to the inner wall of the machine body. The crescent-shaped space is separated by the sliding vanes into a number of fan-shaped chambers.

During one rotation of the rotor, the volume of each fan-shaped chamber will gradually increase from the minimum value to the maximum value, and then gradually decrease from the maximum value to the minimum value. With the continuous rotation of the rotor, the volume of the chambers changes repeatedly according to the above-mentioned law.



Working process diagram of sliding vane compressor

Figure 7: Working process diagram of sliding vane compressor.



1. Air filter 2. Suction regulator 3. Rotor 4. Stator 5. Sliding vanes 6. Compression chamber 7. Compressed air 8. Oil system 9. Oil film 10. Oil/air separator element 11. Cooler 12. Oil filter 13. Minimum pressure valve

3. Liquid Ring Compressor

structure of liquid ring compressor including impellers, cylinder, suction port, liquid ring, discharge port, etc

Figure 8: Simple diagram of liquid ring compressor.



Working principle: The pump body is filled with an appropriate amount of water as the working fluid. Under the action of centrifugal force, the water forms a closed ring of approximately equal thickness determined by the shape of the pump chamber.

The inner surface of the upper part of the water ring is just tangent to the impeller hub, and the inner surface of the lower part of the water ring is just in contact with the top of the blade (in fact, the blades have a certain insertion depth in the water ring). At this time, a crescent-shaped space is formed between the impeller hub and the water ring, and this space is divided into several small cavities by the impeller.

If the upper 0° of the impeller is taken as the starting point, when the impeller in the rotation of the first 180 °, the volume of the small cavity increases from small to large, and it communicates with the suction port. At this time, the gas is inhaled, and when the suction ends, the small cavity is isolated from the suction port.
When the impeller continues to rotate, the small cavity becomes smaller, so that the gas is compressed; when the small cavity is communicated with the exhaust port, the gas is discharged out of the pump.

4. Rolling Piston Compressor

Rotation diagram of rolling piston compressor

Figure 9: Rotation diagram of rolling piston compressor.



1.Intake port 2. Crankshaft 3. Cylinder 4. Rolling piston 5. Exhaust valve

Working principle: The rolling piston compressor, a driven fluid machine that elevates low-pressure gas to high-pressure, is the heart of the refrigeration system. It inhales low-temperature and low-pressure refrigerant gas from the suction pipe, drives the piston to compress it through the operation of the motor, and discharges the high-temperature and high-pressure refrigerant liquid to the exhaust pipe to provide power for the refrigeration cycle.
The rolling piston compressor achieves gas compression by means of the rolling motion of a rotary piston eccentrically arranged in a cylindrical cylinder and the reciprocating motion of a sliding plate in contact with the rolling piston.

5. Scroll Compressor

structure of scroll compressor mainly including orbiting scroll, fixed scroll, etc

Figure 10: Scroll compressor diagram.



The scroll compressor is a compressor with a compressible volume composed of a fixed scroll and an orbiting scroll. The unique design of the scroll compressor makes it an energy-saving compressor in today's world.

Working principle: In the process of suction, compression and exhaust, the fixed scroll is fixed on the frame, and the orbiting scroll is driven by an eccentric shaft and also controlled by an anti-autorotation mechanism. The orbiting scroll rotates in a plane with a small radius around the center of the base circle of the fixed scroll.

The gas is sucked into the periphery of the fixed scroll through the air filter element. With the rotation of the eccentric shaft, the gas is gradually compressed in several crescent-shaped compression cavities formed by the meshing of the fixed and orbiting scrolls, and then continuously sent out from the axial hole of the orbiting scroll.

6. Roots Blower

Structure diagram of Roots blower

Figure 11: Structure diagram of Roots blower.



1. Main oil tank part 2. Gear part 3. Rear bearing seat part 4. Wall plate part 5. Seal 6. Casing part 7. Driving impeller part 8. Driven impeller part 9. Front bearing seat part 10. Auxiliary oil tank part 11. Shaft coupling

Working principle and features: The Roots blower is one of the earliest two-rotor rotary compressors manufactured. The main components of the Roots blower are: rotor, synchronous gear, body (cylinder and end plate), bearing seals, etc.

7. Eccentric Rolling Rotor Compressor

Structure diagram of eccentric rolling rotor compressor

Figure 12: Structure diagram of eccentric rolling rotor compressor.



Working principle: The rotor is eccentrically arranged in the cylinder. When the rotor rotates around the cylinder center O, the rotor rolls close to the inner surface of the cylinder (actually, often with a 0.1-0.2 mm gap). Thus, a crescent-shaped space is formed between the outer surface of the rotor and the inner surface of the cylinder, and its position varies with the rotation angle of the rotor.

The sliding vane separates the crescent-shaped space into two isolated parts, one part is connected with the suction port, and the other part is connected with the exhaust pipe through the exhaust valve. The sliding vane is pressed against the outer surface of the rotor (or guided by two eccentric wheels) by a spring (some having oil pressure function).

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