Types of compressors, their testing and repair

The compressor is one of the main parts of any refrigeration machine, which is necessary to create a pressure difference in the circuit and circulation of the refrigerant due to the transfer of electrical energy from the beginning to the rotation of the engine rotor, then into the movement of the piston, which pumps pressure into the condenser and, as a result, the circulation of the refrigerant in contour. In modern household refrigerators, closed piston compressors are used to circulate the refrigerant and maintain the set temperature in the compartments, which have proven themselves over many years.
Устройство линейного компрессора LG.jpg
Устройство линейного компрессора LG.jpg

Compressor device

The compressor of a household refrigerator consists of a housing (1), inside of which, on a special spring system (2), there is an electric motor (3), the rotation of which drives the piston (4), which, due to the valve system (5), sucks in gas from the low pressure line ( 6) and feeds it to the high pressure line (7).

The compressor motor can be single-phase or three-phase. The principle of operation is the same, but there is a slight difference in that the inverter can change the frequency of the supplied voltage and thereby change the engine speed, while a single-phase motor with a starting winding can only work or not work.

Connecting the compressor

Starting winding of the compressor - is necessary to overcome the rest forces, which are higher than the friction and resistance forces that arise during operation. Many of us have rolled heavy things and know that starting a movement is much more difficult than maintaining it. After the compressor starts, the starting winding is switched off and waits for the next start.
For short-term operation of the starting winding and activating it only at the beginning of operation, start-protection relays are used, which are most often made in two versions.

Electromagnetic starting relay - the place where the starting winding is connected by increasing the current of the working winding, which cannot start, which causes the contacts to close and the starting winding to be connected. After starting, the current drops and the contacts open.

POSISTOR is a more modern way to start a compressor that has low resistance at the normal temperature of its case. As soon as current passes through it (the moment the compressor starts), it begins to heat up and the resistance becomes very high. During operation, its “open” state is maintained by low currents. This system is very reliable, but during voltage surges it can damage the compressor, which cannot start with an “uncooled” posistor, which can consequently lead to burnout of the starting winding.

Protection relay - also all compressors have a protection device or protection relay, which works on the principle of heating a nichrome wire. And in the event of an increase in current (compressor malfunction) or deformation of the plate, the power contacts of the working winding close. This protection relay can be located together with the starting device, as in most compressors, or built inside, such as on Danfoss compressors.

The principle of operation

The crank and linear principle of operation is the main difference in the operating principle of modern compressors used in domestic refrigeration. And if the principle of operation of the crank mechanism is clear, then the linear compressor operates on the principle of a relay that pulls in or pushes out the core. In addition, you can adjust the amplitude of these shocks and thereby change performance. But such compressors are very expensive, and in case of repair, the consumer may be in for an interesting surprise.

The device for compressor wedging is made on two diodes and can start the compressor in vibrator mode with a frequency of 50 Hz, which very often leads to wedging of the piston. But very often this has only a temporary effect, since the system is sealed and does not have the ability to be completely flushed. It is, of course, possible to purge the circuit (for example, with nitrogen or flushing freon), but completely replacing the oil or cleaning the valves is almost impossible without rough intervention (“grinder”) in the compressor housing. Therefore, we do not recommend using this method, but in some cases, as a temporary measure, it can help.

Compressor compatibility in household refrigerators

When replacing compressors, one of the main parameters is its rated power, and here you need to be as precise as possible. But it is also worth noting that many craftsmen take the average setting of 160-170 W and put it on all refrigerators. This is not the right thing to do and it is better to select power close to the rated one.

When it comes to oil compatibility, it is also worth noting that a very important parameter is the type of oil found in the compressor itself. On R12 and R600 it is mineral, and on R134 it is synthetic refrigeration oil, which has a low moisture content and does not allow long exposure to open air.

Attention!!! Do not use automobile oil in compressors of household refrigerators!

The oil level in the compressor is low, and lubrication is carried out through channels and splashing during operation. During transportation, the compressor may be on its side, and oil may flow onto the circuits and walls. Therefore, after transportation, the refrigerator must be placed vertically and not turned on for several minutes to allow the oil to drain and reach its working level. Otherwise, it may damage the piston group and the compressor will fail.

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