Basic knowledge of refrigeration compressor
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 the 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? There are differences between the base oils of POE oil (R410a) and mineral oil (R22), 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, it will reduce the service life of the compressor. 3. Confirm the location of fluoride in the 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 reservoir. When the system starts, the liquid refrigerant will continuously hit the cylinder, causing the compressor to cause liquid shock. The damage to the compressor is extremely fatal. At the same time, the liquid refrigerant may stick to the wiring after directly 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. 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 large, 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 starting; After a long period of shutdown, there is too much liquid refrigerant in the compressor-the starting load increases; 5. The condensation temperature is 6℃ lower than the bottom of the compressor During continuous operation; T should be above 6℃; during intermittent operation; T should be above 0℃, control the meaning of T Compared with the condensation temperature (equivalent to the saturation temperature of the internal pressure of the casing), when the bottom temperature of the compressor is low, the refrigerant will continuously condense in the compressor. At this time, the oil is diluted by the refrigerant, resulting in insufficient oil film strength and serious wear on the sliding parts . The requirement of T 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 T: Excessive amount of refrigerant enclosed; capillary is not suitable; excessive cooling of the compressor; Frequent, short-time intermittent operation. 6. Motor winding temperature When the operating conditions are at the maximum load, it should be below 127°C. Measurement method: Within 3 seconds after the compressor stops, measure the resistance of the main winding with a Wheatstone bridge or a digital ohmmeter, and then calculate according to the following formula: Winding temperature t℃=[R2(T1+234.5)/R1]－234.5 R2: measuring resistance; R1: winding resistance in cold state; T1: cold motor temperature If the winding temperature exceeds the service conditions, the possible defects: The speed of aging of winding enameled wire is accelerated (motor burned out); Insulation material binding wire, insulation paper aging speed faster (the insulation life is halved for every 10℃ increase in temperature); Deterioration of oil due to overheating (decreased lubrication performance); 7. Built-in overload protector Built-in overload protector; the contact is normally closed during normal operation. When the internal temperature of the compressor sensed by the built-in overload protector rises, the bimetal will act and drive one pole of the contact to trip and cut off the normally closed contact The current loop protects 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, and the other is the temperature sensed by the metal casing 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. The 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. Zui will eventually achieve the role of temperature control. 9. Operate after fluorine charging and then check the electrical performance 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 the system should specify the vacuum degree 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 parts and have a fatal impact on the compressor. 3. There will be copper plating, which will affect the fitting gap and sealing effect of the parts; severe copper electroplating will directly cause the blocking of the matching parts. 4. The refrigerant will decompose; 5. Air is non-condensable gas, resulting in high system pressure and unstable working conditions; 11. Precautions during system vacuum Under vacuum, the compressor is strictly prohibited from running or applying electrical pulses. Because electrons are easily released under vacuum, discharge occurs. However, if there is a medium (such as refrigerant and air) between the charged bodies, the electrons will not be easily separated. 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 point. 2. The oil+refrigerant mixture is intercepted during the test, and the test 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. Precautions for the use of refrigeration compressors 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 enters in the air conditioning system The source of system residues may be A. Fine copper shavings are produced when the copper pipe is cut. B. Foreign materials 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. System water inlet The moisture content in the air conditioner system should be controlled below 75ppm (recommended value). A. Ways for water to enter: B. Air conditioner enters water during the manufacturing process; C. The refrigerant contains more water; D. Water leakage caused by system leakage 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. ③ Remove the heat generated by friction in time. If the refrigerating machine oil fails to return smoothly, the system has insufficient oil return, resulting in 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 not suitable (the piping is too long and the diameter is large); Operating under extremely low temperature conditions; Intermittent operation interval is short; 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 surface of the exhaust valve plate is frozen with carbonized oil. 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 a leak that reduces the refrigerant. Such a long-term operation, so that the heat generated by the motor cannot be carried out by the refrigerant; the exhaust temperature will also increase accordingly, when the temperature is too high, R22 begins to thermally decompose, generating 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 reception 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.
