Can you answer these common basic knowledge questions about refrigeration compressors?

Can you answer these common basic knowledge questions about refrigeration compressors?

1. Why should the compressor run continuously for at least 5 minutes, and stop for at least 3 minutes after shutting down before restarting?

　　 After shutting down, stop for at least 3 minutes before starting again to eliminate the pressure difference between compressor inlet and outlet. Because in the case of a large pressure difference, the starting torque of the motor will increase, causing the current to rise to a certain level, the protector will act and the compressor cannot continue to run.

　　2, can R410A/R22 lubricants be mixed?

The base oils of POE oil (R410a) and mineral oil (R22) are different, especially the difference in hygroscopicity. If POE oil is used for R22 refrigerant and the system does not add a dryer according to the system requirements of R410a, it will cause capillary blockage and motor Poor insulation.

　　 Depending on the refrigerant, the emphasis and amount of additives in lubricating oil are also different. Generally, R22 mineral oil focuses on adding antioxidants and defoamers, while POE oil focuses on adding antioxidants and acid scavengers. When the two are mixed, the service life of the compressor will be reduced.

　　 3. Confirmation of fluorine filling position of air conditioner

　　 Refrigerant can generally be added in three places: the condenser, the receiver side of the compressor, and the evaporator.

Add liquid to the accumulator. When the system starts, the liquid refrigerant will continuously impact the cylinder, causing the compressor to produce liquid shock, which is extremely fatal to the compressor. At the same time, the liquid refrigerant may stick to the wiring directly after entering the compressor. The terminal causes instantaneous insulation and poor withstand voltage; similarly, this situation can also occur when liquid is added to the evaporator side.

As for the condenser, due to its relatively large volume, it can store sufficient amount of refrigerant, and at the same time, it will not cause adverse consequences when starting, and the charging speed is fast and safe; therefore, the condenser is generally filled with liquid method.

　　4, the maximum allowable charge

　　 The amount of refrigerant enclosed in the compressor should be controlled within the allowable range. If the amount of refrigerant enclosed is too much, the following defects may occur:

　　Insulation resistance decreased;

　　 Excessive liquid return flow---liquid compression;

　　Oil is diluted by refrigerant --- poor lubrication;

　　 Unstable working ability; increased balance pressure --- poor start-up;

　　 Too much liquid refrigerant in the compressor after a long period of inactivity---starting load increases;

　　5, the condensation temperature is 6℃ lower than the bottom of the compressor

　　During continuous operation, ΔT should be above 6℃; when intermittent operation, ΔT should be above 0℃. The meaning of controlling ΔT:

Compared with the condensation temperature (equivalent to the saturation temperature of the internal pressure of the shell), when the temperature at the bottom of the compressor is low, the refrigerant will continue to condense in the compressor. At this time, the oil is diluted by the refrigerant, resulting in insufficient oil film strength and severe wear of sliding parts. . The requirement of ΔT is to ensure that the refrigerant does not condense in the compressor to prevent the occurrence of the above-mentioned defects.

　　 Common causes of low ΔT:

　　 Too much refrigerant is enclosed;

　　The capillary is inappropriate;

　　 Overcooling of the compressor;

　　 Frequent, short-time intermittent operation.

　　6, motor winding temperature

　　When the use condition is at the maximum load, it should be below 127℃.

　　 Measurement method: Within 3 seconds after the compressor stops, use a Wheatstone bridge or digital ohmmeter to measure the resistance of the main winding, and then calculate it according to the following formula:

　　 Winding temperature t°C = [R2(T1+234.5)/R1]-234.5

　　 R2: Test resistance; R1: Winding resistance in cold state; T1: Cold state motor temperature

　　If the winding temperature exceeds the service conditions, the possible defects:

　　The aging speed of winding enameled wire is accelerated (motor burnt out);

　　Insulation material binding wire, insulation paper aging speed faster (the insulation life is halved for every 10℃ increase in temperature);

　　 oil deterioration due to overheating (decreased lubrication performance);

　　7, built-in overload protector

The contact of the "built-in overload protector" is normally closed during normal operation. When the internal temperature of the compressor sensed by the "built-in overload protector" rises, the "bimetal" acts to drive one pole of the contact to be normally closed The contact trips to cut off the current loop and protect the compressor. Because the "built-in overload protector" is connected to the C end of the press sealed terminal, the main and auxiliary coils can be protected at the same time.

　　The bimetal is temperature-triggered for protection. The trigger temperature source comes from two parts: one is the electric heating heat when the current passes through, and the other is the temperature sensed by the metal shell of the "built-in overload protector".

　　 8. Thermal switch and thermistor for frequency conversion

　　The thermal switch and the thermistor have nothing to do with the compressor wiring and are not directly connected in series in the compressor circuit.

　　Thermal switch controls the on and off of the compressor control circuit by sensing the temperature of the compressor cover.

　　 Thermistor is a negative temperature characteristic element with feedback signal output to the microprocessor. Pre-input a set of temperature and resistance value tables in the microprocessor. Every time a resistance value is measured, the corresponding temperature can be reflected in the microcomputer. z* finally achieves the function of temperature control.

　　9. Operate first and then check the electrical performance after fluorine filling

　　After the liquid refrigerant is sealed, the charged liquid refrigerant may condense on the terminal. The insulation resistance of the liquid refrigerant is much lower than that of the gaseous refrigerant, and the insulation level of the whole machine will drop instantly. After operation, the liquid refrigerant evaporates and the insulation will return to normal.

　　 10. Why does the system require vacuum

　　The degree of vacuum directly affects the water content in the system. The lower the degree of vacuum, the less water vapor remains in the system.

　　1. The capillary tube and expansion valve are blocked by ice during heating;

　　2. The acidic environment caused by moisture will aggravate the deterioration of oil and the burning of the motor; it will corrode the components and have a fatal impact on the compressor.

　　3. The phenomenon of "copper plating" will occur, which will affect the fitting gap and sealing effect of the parts; serious copper plating will directly cause the blocking of the matched parts.

　　 4. The refrigerant will decompose;

5.The air is a non-condensable gas, resulting in high system pressure and unstable working conditions; 11. Matters needing attention when the system is under vacuum

　　 In the vacuum state, the compressor is strictly prohibited to operate or apply electrical pulses.

　　Because electrons are easily dissociated in a vacuum state, electrical discharge occurs. However, there is a medium (such as refrigerant, air) between the charged bodies, and the electrons are not easy to free.

　　 12. How to judge whether the oil level and oil volume are appropriate

　　 There are two main types of confirmation:

　　1. Observe through the sight glass to observe whether the oil in the compressor is abnormally transferred to the system under various working conditions (including special working conditions), and whether there is a drop in the oil level at a special time.

　　2. Intercept the mixture of oil + refrigerant during the test, and test that the oil dilution rate does not exceed the allowable value.

　　Through the above measures, we can basically determine whether the oil return and refrigerant charge of a system are suitable for the reliability of the compressor. The compressor is compatible with the air-conditioning system, and simple tests cannot fully assess all the problems that may occur during long-term operation.

　　Compressor use matters needing attention

　　 1. Compressor wrong wiring

　　 There is only one correct wiring method for the compressor, and all others are wrong. Due to incorrect wiring, the thermal protector may lose its protection function, which may cause the compressor to burn out, and generally cause the auxiliary coil to burn out.

　　 For three-phase compressors, there must be a phase sequence protection device

　　2, foreign matter in the air conditioning system enters

　　The sources of system residues may include:

　　A. Small copper chips are produced when the copper pipe is cut.

　　B. Foreign matter such as processing oil and impurities in the system manufacturing process

　　C. The compressor is exposed to the air for a long time, and dust and water vapor enter.

　　D. During welding, an oxide film will be formed on the inner surface of the pipeline, so nitrogen should be filled for protection during welding

　　The impact of residues on the system:

　　A. It will aggravate the wear of the friction surface of the moving parts and block the pump oil passage;

　　B. When the compressor contains small inclusions such as moisture, fiber, dust, etc., it may be adsorbed on the motor windings and terminals, reducing the insulation performance of the whole machine;

　　C, processing oil, etc. will also react with refrigerant or refrigerating machine oil to produce sludge and coke, which adhere to the exhaust valve plate, suction filter, and capillary, causing blockage;

　　3, the system enters water

　　 The moisture content in the air conditioner system should be controlled below 75ppm (recommended value).

　　A, the way water enters:

　　B. The air conditioner enters water during the manufacturing process;

　　C. The refrigerant contains more water;

　　D, system leakage causes water intrusion;

　　E, the compressor is improperly sealed and placed open;

　　F. The vacuum of the system does not meet the standard;

　　G, incomplete venting during installation;

　　 4. Insufficient oil return in the system

　　Refrigeration oil function:

　　①Lubricate, effectively prevent mechanical parts from wearing.

　　②Oil seal function to maintain high and low pressure difference.

　　③Remove the heat generated by friction in time.

　　 If the refrigerating machine oil cannot be returned smoothly after being drained, the oil return of the system is insufficient, causing:

　　 Poor oil return may occur;

　　 Poor lubrication leads to wear and seizure of moving parts;

　　The compressor capacity is reduced;

　　 overheating;

　　 The main reasons for poor oil return:

　　 Too much refrigerant, the oil discharge increases;

　　The piping is inappropriate (the piping is too long and the pipe diameter is large);

　　Operating under extremely low temperature conditions;

　　 Short intermittent operation interval;

　　 The amount of refrigerant circulating is small and the pressure is low;

　　The capillary is inappropriate;

　　5, overload operation

　　 The compressor has a maximum operating condition. If it exceeds the allowable range, the following consequences will occur:

　　A. Because the exhaust temperature is too high, the refrigerant oil on the surface of the exhaust valve plate is carbonized.

　　B. Due to the excessive pressure difference between pump body height and low pressure, the blade groove is worn.

　　C. The service life is reduced.

　　 6. Leakage of refrigerant

　　 The air-conditioning system has reduced refrigerant due to leakage. After such a long-term operation, the heat generated by the motor cannot be taken out by the refrigerant; the exhaust temperature will rise accordingly. When the temperature is too high, R22 will begin to thermally decompose to produce acid and water. It will also free the carbon in the refrigerating oil and generate carbon deposits; refrigerant leakage will also cause poor oil return.

　　7, abnormal power receiving

　　 There are a lot of motor main coils or auxiliary coils overheating uniformly, which is obviously different from the short circuit of the motor itself.

　　The uniform overheating of the motor is generally caused by the impact of external large current or long-term overheating. Such as abnormal voltage, low temperature and low voltage start, etc.