If the test chamber can still be cooled, it means that there is no external factor for cooling water. The temperature cannot be maintained. If the compressor can start when the test box is running, the electrical circuit from the main power supply to each compressor is normal, and there is no problem in the electrical system. After checking the electrical system, if there is no problem, you can't relax and check the cooling system. First check the discharge and suction pressures of the low-temperature (R23) compressors of the two refrigeration units are lower than normal, and the suction pressure is evacuated, indicating that the main refrigeration unit has insufficient refrigerant quantity. Touch the exhaust and suction lines of the R23 compressor of the main unit by hand, and find that the temperature of the exhaust line is not high, and the temperature of the suction line is not low (no frost). Lack of refrigerant, the system leaks fluorine.
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After the above experiments, if the cause of the failure is still not confirmed, it is necessary to further confirm the cause of the failure in conjunction with the control process of the test chamber. The main unit and auxiliary unit are two sets of refrigeration units in the test box. When the cooling rate is large, the two sets of units work at the same time. At the beginning of the temperature maintenance phase, the two sets of units still work at the same time. When the temperature starts to stabilize, the auxiliary unit stops working, and then the host group maintains the temperature stability. If the host group R23 leaks, the cooling effect of the host group will be insignificant. Since the two units are working at the same time during the cooling process, there is no phenomenon that the temperature is not stable, and the cooling rate is indicated to decrease. In the temperature maintenance stage, once the auxiliary unit stops working and the main unit has no cooling effect, the air in the test chamber will slowly rise. When the temperature rises to a certain level, the control system will start the auxiliary unit to cool down and lower the temperature to the set point. Near the fixed value (55 degrees below zero), and then the auxiliary unit stops working again, and so repeatedly, a malfunction will occur. Then at this time, it can be determined that the source of the fault is the refrigerant R23 of the low-temperature (R23) unit of the host group.
Finally, the refrigeration system should be checked for leaks. The main method is to use a leak detector and soapy water to check. It is found that the stem of a hot gas bypass solenoid valve is cracked by about 1 cm. Replace the solenoid valve, recharge the system with fluorine, and the system is operating normally.
Through this analysis from the outside to the inside, I think that large and small faults can be found out, as long as you know the cause of the fault, you can directly find a way to solve it. Inspection methods like this are carried out every once in a while, so as to facilitate the maintenance and repair of machinery.