In the practice of the relevant faults and their handling, it is expected to explore the general method of fault diagnosis of marine refrigeration equipment. Some faults of a certain refrigeration system and its analysis and treatment, the round refrigeration system uses two one-shrinking machine, no cylinder unloading mechanism, the refrigerant is three fish bank and vegetable warehouse, the round mainly travels to the domestic north-south route The grain replenishment cycle is not long, so in order to improve the economy, the temperature of the reservoir is set for the meat store and the fish bank. The temperature of the cold storage can not be lowered. The chef reports that the fish warehouse is too high. It was found that the liquid supply solenoid valves of only one or two banks in the two banks were in the open state, the compressor started frequently, and the situation did not improve when switching to another compressor, but there was a thick frost on the return pipe.
Into these two libraries, it was found that there was a thick frost on the evaporating coil, and the situation was improved after the defrost. At this time, the number of starts of the compressor was reduced, and the temperature of the reservoir was also reduced, but it was not ideal enough. Later, the upper and lower limits of the operation of the low-voltage controller were checked, and it was found that the pressure was misregulated to the gauge pressure, that is, the pressure was stopped at the time, and the pressure was started from time to time, and the corresponding evaporation temperature range was about one. It is too high, and the amplitude difference is too small. Therefore, the upper and lower limits of the low-voltage controller are re-adjusted, and the adjusted value is the lining. After the corresponding evaporating temperature range is about one, the system is restarted and the work returns to normal.
In general, there are four main reasons for the frequent start-up of refrigeration compressors. There are leaks between high and low pressures. If the suction and exhaust valve is not closed, the oil return valve of the oil separator or the solenoid valve is not closed. In this case, when the temperature of the reservoir drops to the lower limit, the compressor is quickly returned due to leakage, causing the compressor to start, and the compressor quickly evacuates the low-pressure line, so that the compressor starts frequently.
The circulating amount of the refrigerant is too small. When the storage temperature does not reach the lower limit, the compressor has pumped the low pressure line to the lower limit pressure of the low pressure relay and stops, but the solenoid valve has not been closed, and the compressor is started up due to the suction pipe pressure rising, thereby starting frequently. Since the thermal resistance is greatly increased, the evaporation amount is significantly reduced, the temperature of the reservoir is not lowered, the superheat of the return air is too small, even the wet steam, the opening of the expansion valve is insufficient, the circulation of the refrigerant is reduced, and when the compressor is quickly evacuated, It will start frequently. Obviously, the two faults of the low-voltage relay ship refrigeration device are found and excluded. The amplitude of the Yangqiguan is too small. When the lower limit pressure is too high, even if the temperature does not drop to the specified value, the compressor has reduced the suction pressure to the lower limit pressure. After stopping, the solenoid valve is still open, and the suction pressure quickly rises to the upper limit pressure, so that the compressor starts frequently, and the cooling capacity is also reduced due to frequent starting.
In addition, if the lower limit pressure is too high, the average evaporation temperature is too high. When the heat transfer temperature difference between the evaporator and the cold storage is insufficient, the storage temperature is difficult to drop, which is one of the reasons why the cold storage temperature of the cold storage is too high.
Among the reasons for the frequent start-up of the compressor, there are differences and intrinsic links. For example, in the first case, when the high and low pressure leaks are not large, the storage temperature can generally meet the requirements, and the compressor starts frequently. Appears when the valve is closed. Based on this, this fault can eliminate the possibility of high and low pressure leakage, which is not improved when the compressor is tested. The oil return pipe of the oil separator is not hot, and the two reservoirs supply electromagnetic The valve is fully open and fully confirmed.
As for the expansion valve blockage or insufficient refrigerant, in addition to the frequent start of the compressor and the short start-up time, it is generally accompanied by a high return air temperature, frost melting on the return pipe, etc., when the system fails, it is just the return pipe. The frosting has increased or not, and the situation has not improved when switching to the manual expansion valve, and this possibility can be eliminated.
Then, the cause of the failure of the refrigeration system can only be the latter two cases. First of all, the frost on the evaporator coil should not exceed the frost thickness, which leads to an increase in thermal resistance. Even if there is a certain heat transfer temperature difference between the evaporator and the cold storage air, the refrigerant will not be fully absorbed in the evaporator. The heat is vaporized, and a large amount of refrigerant absorbs heat and vaporizes on the return line, which increases the frosting of the return line. In addition, since the superheat of the expansion valve is too small or even zero, the compressor is turned off or closed, and the compressor is quickly The refrigerant is evacuated and stopped, but the solenoid valve is not closed. The cold storage still has a certain heat load. After the evaporator pressure rises, the compressor starts again, causing frequent start-up and thicker evaporator frost. This situation is more serious.
In fact, the frost on the two low-temperature cold storage evaporator coils of the system is too thick, up to 1 or even thicker, which has seriously affected the heat transfer, and the storage temperature is not likely to fall.
After the defrosting, the system is operated again, and the temperature of the two low temperature reservoirs can be reduced to the next time. The upper and lower limits of the low voltage relay operation are misadjusted to the left and the amplitude difference is only the word, and the evaporator frost layer is too thick and evaporated. The amount is reduced, and the suction pressure can be quickly reduced to ton after the start of the jade shrinking machine, and it is not surprising that the evaporation temperature is only one or two.
For the adjustment of the lower limit of the low-voltage relay, the refrigerant saturation temperature corresponding to the design evaporation temperature is generally reduced. The temperature of the system is set to a design evaporation temperature. The lower limit of the low-voltage relay should be set to one. Corresponding saturation pressure, that is, the upper limit of the low-voltage relay generally takes a temperature lower than the upper limit temperature corresponding to the saturation pressure value. In addition, for the 12 system, the amplitude difference of the low-voltage relay generally takes one (about one time according to this, the amplitude is taken When the difference is the upper limit pressure, the corresponding evaporation temperature is about one. After the adjustment, the evaporation temperature can be kept in between, ensuring sufficient heat transfer temperature difference between the evaporator and the air, and the storage temperature can be lowered to the regulation. The range, the compressor also started normally due to the recovery of the amplitude difference.
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