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Basic knowledge of refrigeration compressors! Did you know everything

Basic knowledge of refrigeration compressors! Did you know everything Why should the compressor run continuously for at least 5 minutes, and stop at least 3 minutes after shutdown to restart? Stop at least 3 minutes after shutting down to start again in order to eliminate the pressure difference between the compressor inlet and exhaust. Because in the case of a large pressure difference, the starting torque of the motor will increase, and when the current rises to a certain level, the protector will act and the compressor cannot continue to run. Can 2R410A/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 performance. Depending on the refrigerant, the emphasis and amount of additives in the lubricant also vary. In general, R22 mineral oil focuses on the addition of antioxidants and defoamers, while POE oil focuses on the addition of antioxidants and acid scavengers. When the two are mixed, it will reduce the service life of the compressor. 3 Confirm the location of the air-conditioning fluoride Refrigerant can generally be added in three places: condenser, accumulator side of compressor, and evaporator. Add liquid at the reservoir. When the system starts, the liquid refrigerant will continuously hit the cylinder, causing the compressor to produce liquid shock. The damage to the compressor is extremely fatal. At the same time, after the liquid refrigerant directly enters the compressor, it may stick to the wiring On the terminal, it causes instant insulation and poor voltage resistance; similarly, this situation also occurs when adding liquid on the evaporator side. For the condenser, due to its relatively large volume, it can store a sufficient amount of refrigerant, and at the same time, it will not produce adverse consequences when starting, and the charging speed is fast and safe; so the liquid filled at the condenser is generally used method. 4 Maximum allowable charge When the compressor is used, the amount of refrigerant enclosed 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 capacity; increased balance pressure-poor starting; Too much liquid refrigerant in the compressor after a long period of shutdown-the starting load increases; 5 The condensation temperature is 6℃ lower than the bottom of the compressor During continuous operation, ΔT should be above 6℃; during intermittent operation, ΔT should be above 0℃. Control the meaning of ΔT: Compared with the condensation temperature (equivalent to the saturation temperature of the internal pressure of the casing), when the compressor bottom temperature 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 serious wear on the sliding parts . The prescribed ΔT is to ensure that the refrigerant does not condense in the compressor to prevent the above-mentioned problems. Common causes of low ΔT: Excessive amount of refrigerant enclosed; The capillary is not suitable; Excessive cooling of the compressor; Intermittent operation with frequent, short-term operation. 6 Motor winding temperature The operating conditions should be below 127℃ when the maximum load is reached. Measurement method: Within 3 seconds after the compressor stops, measure the resistance of the main winding with a Wheatstone bridge or 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 usage conditions, the possible defects are: Aging speed of winding enameled wire is accelerated (motor burned out); The aging speed of insulation material binding wire and insulation paper is accelerated (the insulation life is halved every time the temperature rises by 10°C); Oil degradation due to overheating (decreased lubrication performance); 7 Built-in overload protector The "Built-in overload protector" contact is normally closed during normal operation. When the internal temperature of the compressor sensed by the "Built-in overload protector" rises, the "bimetallic plate" acts, driving the pole of the contact to be normally closed. The contact jumps open to cut off the current loop and protect the compressor. Because the "built-in overload protector" is connected to the C terminal of the sealed terminal of the press, the main and auxiliary coils can be protected at the same time. The bimetallic strip is triggered by temperature 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 shell of the "built-in overload protector". Thermal switch and thermistor for frequency conversion Both 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. The thermistor is a negative temperature characteristic element with a feedback signal output to the microprocessor. Enter a set of temperature and resistance value tables in advance in the microprocessor. Each measured resistance value can reflect the corresponding temperature in the microcomputer. Eventually achieve the role of temperature control. 9 After filling with fluoride, first run and then check the electrical performance After the liquid refrigerant is enclosed, 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 phenomenon of instantaneous insulation degradation of the whole machine may occur. After operation, the liquid refrigerant evaporates and the insulation returns to normal. 10 Why the system must specify the degree of 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. Ice blocking of capillary tube and expansion valve during heating; 2. The acidic environment caused by moisture will exacerbate oil degradation and motor burnout; it will erode parts and components and have a fatal impact on the compressor. 3. The phenomenon of "copper plating" will occur, which affects the fitting gap and sealing effect of the parts; the severe copper plating phenomenon will directly lead to the blocking of the matching parts. 4. The refrigerant will decompose; 5. Air is non-condensable gas, which leads to high system pressure and unstable working conditions; 11 Points to note when the system is in vacuum Under vacuum, the compressor is strictly prohibited from running or applying electrical pulses. Because in a vacuum state, electrons are easily released, so 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 typ es of confirmation: 1.Look in the sight glass to observe whether the oil in the compressor is abnormally transferred to the system under each working condition (including special working conditions), and whether the oil level at a particular time point is reduced. 2. Intercept the mixture of oil and refrigerant during the test, and the test oil dilution rate shall not exceed the allowable value. Through the above measures, we can basically determine whether the oil return and refrigerant charge of a system are appropriate for the reliability of the compressor. The compressor is compatible with the air-conditioning system. A simple test cannot fully assess all the problems that may occur during long-term operation. Notes on the use of refrigeration compressors Compressor miswiring The compressor has only one correct wiring method, the others are wrong. Due to miswiring, the thermal protector may lose the protection function, which will cause the compressor to burn out, generally causing the secondary coil to burn out. For three-phase compressors, phase sequence protection devices are required. 2 Foreign matter in the air conditioning system The sources 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 generated on the inner surface of the pipeline, so it is necessary to protect it with nitrogen during welding Effects 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 moisture, fibers, dust and other small inclusions, it may be adsorbed on the motor windings and terminals, reducing the insulation performance of the whole machine; c. Process oil, etc. will also react with the refrigerant or refrigerating machine oil to produce sludge and coke, which will adhere to the exhaust valve, 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. The air conditioner enters the water during the manufacturing process; c. The refrigerant contains more water; d. The system leakage causes water intrusion; e. The compressor is improperly sealed and placed open; f. The vacuum of the system has not reached the standard; g. Incomplete emptying during installation; 4 Insufficient oil return from the system Refrigerating machine oil function: ①Lubrication, effectively prevent wear of mechanical parts. ②Oil seal function to maintain high and low pressure difference. ③ Remove the heat generated by friction in time. If the refrigerating machine oil cannot be returned smoothly after being discharged, the system does not return enough oil, resulting in Poor oil return may occur; Poor lubrication leads to wear and sticking of moving parts; Reduced compressor capacity; overheat; The main causes of poor oil return: Too much refrigerant will increase the amount of oil discharged; The piping is not suitable (the piping is too long and the diameter is large); Operate under extremely low temperature conditions; Intermittent operation interval is short; Low refrigerant circulation and low pressure; The capillary is not suitable; 5 Overload operation The compressor has the maximum operating conditions. If it exceeds the allowable range, it will cause the following consequences: a. Because the exhaust temperature is too high, the freezing oil on the surface of the exhaust valve is carbonized. b. The blade groove is worn due to the excessive pressure difference between the height of the pump body. c. Service life is reduced. 6 refrigerant leakage The refrigerant in the air-conditioning system is reduced due to leakage. 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 freezing oil to form carbon deposits; refrigerant leakage will also cause poor oil return. 7 Abnormal power reception There are many motors whose main coils or auxiliary coils are evenly overheated, and the difference between the turns of the motor itself is obvious. 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.

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