Refrigeration Compressor Usage And Common Maintenance Tips

Appearance inspection

If the compressor capacitor is found to have shell deformation, bulges, cracks, leakage, etc., it means that the capacitor has been damaged and can no longer be used. The replacement capacitor should be of the original specification and model as much as possible and cannot be replaced at will. The capacitor capacity will attenuate due to the harsh use environment and over time. Generally, if the attenuation is greater than 20%, it will cause difficulty in starting, large starting current, and long starting time; especially when the power supply voltage is lower than 20%, it will Startup tripping, overcurrent protection, and even compressor burnout may occur. Therefore, when starting is difficult, starting time is too long, instantaneous tripping, etc., the capacitor must be checked first.

Compressor terminal identification and winding DC resistance detection

Although the terminal positions of compressors from different manufacturers are different, letters are marked next to each terminal; for single-phase compressors, C represents the common terminal, R represents the main winding terminal, and S represents the auxiliary winding terminal. Each winding must be wired as shown in the diagram, otherwise the compressor will not work properly or even burn out. The determination method of the common terminal C, the main winding terminal R, and the auxiliary winding terminal S of a single-phase compressor: According to the principle that the main and auxiliary windings of a single-phase compressor have different wire diameters and number of turns, and the DC resistance values are also different (the main winding The resistance value of C~R is small, and the resistance value of auxiliary winding C~S is slightly larger. The resistance value of R~S is the sum of the resistance values of the main and auxiliary windings. Only the test lead is in contact with the assumed common terminal, and the other test lead is in contact with the other two terminals respectively to measure the resistance. Assuming it is correct, then the other end with a smaller resistance value is the main winding terminal R, and the other end with a slightly larger resistance value is the auxiliary winding terminal S. Using the same method and assuming three more times, you can find the common terminal C, the main winding terminal R and the auxiliary winding terminal S.

Three-phase compressor wiring method and approximate resistance value

Although the terminal positions of three-phase compressors from different manufacturers are different, the letters U, V, and W are marked next to each terminal. After being identified by the phase sequence protector, A corresponds to U; B corresponds to V; C corresponds to W. In addition, you can also connect the wiring according to the color of the compressor wire set, that is: red represents phase A connected to the U terminal; white represents phase B connected to the V terminal; blue represents phase C connected to the W terminal. The wiring of each winding must be as shown in the diagram, otherwise the compressor will reverse. Since the three windings of a three-phase compressor have the same wire diameter and number of turns, their DC resistance values are also the same (the same is true for inverter compressors). For example: the measured resistance of one winding of a three-phase compressor is equal to 2.2 ohms. , the remaining two windings must be equal to 2.2 ohms respectively, that is, U~V=V~W=W~U=2.2 ohms.

Compressor insulation resistance measurement:

Before the refrigeration compressor leaves the factory, the insulation resistance value between the compressor terminal and the shell should be greater than 2 megohms. This is a requirement for air conditioners before leaving the factory. In fact, due to the harsh operating environment of air conditioners, this standard can no longer be used to judge the quality of insulation after running for a period of time. Generally, it is considered normal if it is not less than 1 megohm, but 1 megohm is measured with a 500V megger. You cannot use a multimeter to measure the insulation resistance, because the internal power supply voltage of the multimeter is only 9V, and the measured insulation resistance value is meaningless.

Maintenance of compressor protector

The compressor will protect itself if it is overloaded or overheated. There are two types of protection devices: built-in and external. Here we only talk about the external type. If the compressor cannot start automatically after 3 minutes of protection, it means that the protector has acted. After protection occurs, because the compressor body temperature is high and heat dissipation is slow, the reset time of the protector is long, generally 3 to 15 minutes, and up to 30 minutes. If it still cannot start after 30 minutes, the overload and overheat protector may be damaged.

Precautions when repairing the compressor

Oxygen is colorless and odorless. It does not burn and is not explosive by itself. However, when mixed with other flammable or explosive gases, it will support combustion or explosion. Especially with oil, it can produce violent chemical reactions and explode instantly. The Refrigeration Encyclopedia public account reminds that because there is lubricating oil in the compressor, it is forbidden to blow the system with oxygen and keep the oxygen cylinder away from the compressor maintenance site. Otherwise, it will cause serious consequences of the compressor exploding or even the system exploding at the same time.

Dealing with difficulty in random starting and shaft holding (cylinder jamming)

Difficulty starting and shaft holding are two completely different fault phenomena and must be treated differently. When the compressor capacitance capacity decays to 60% of its original value, when the outdoor ambient temperature is below minus 5 degrees, when the power supply voltage is below 15%, and when the system pressure is not yet balanced. These factors will cause difficulty in starting the compressor. In fact, shaft holding and cylinder jamming mean the same thing, which means that the compressor is faulty or the compressor is damaged. The main reason for cylinder jamming is that the system is dirty or lacks oil. The Refrigeration Encyclopedia official account reminds that under normal circumstances, the cylinder block and valve plate will There are varying degrees of damage, which in principle cannot be repaired or cannot be repaired, and a new compressor needs to be replaced. However, there is a lot of experience in dealing with cylinder jamming, and some compressors with less severe cylinder jamming can be saved by knocking, increasing capacitance, etc.

Determine whether the compressor motor winding is short-circuited

Use a multimeter to measure the resistance at two points C-R or C-S of the compressor motor winding. If the resistance value of the measured winding is less than the normal value, it can be judged that the winding is short-circuited. For a three-phase motor, use two test leads to touch two of the three terminals. If the resistance values measured three times are consistent, it indicates that the winding is good; if the resistance value measured two times is infinite, it indicates that there is a set of windings. Open circuit; if the three tests are infinite, it indicates that at least two sets of windings are open circuit; if the resistance measured in two of the three measurements is significantly smaller than the other, it indicates that there is a short circuit.