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What should we do if the low temperature of the high low temperature test chamber cannot be maintained? Firstly, observe whether the refrigeration compressor can be started during the operation or not. If the compressors in the high and low greenhouse can be started during operation, it means that the electrical circuits of the main power supply to the compressors are normal, and the electrical system is also normal.
If there is no problem with the electrical system of the high low temperature test chamber, continue to check the refrigeration system. Firstly check the two sets of refrigeration compressor units in the high low temperature test chamber. If the discharge and suction pressures of the low-temperature compressors are lower than normal, and the suction pressure is evacuated, this indicates that the refrigerant quantity of the main refrigeration unit is obvious insufficient. Then touch the exhaust and suction pipes of the main unit compressor in the high low temperature chamber. If you find that the temperature of the exhaust pipe is not high, and the temperature of the suction pipe is not low (no frost), this indicates the lack of refrigerant in the main refrigeration unit.
High low temperature test chamber is consisted of the main unit and the auxiliary unit. When the cooling rate is large, the two groups of units work at the same time. At the beginning of the temperature maintaining phase, the two groups of units still work at the same time. When the temperature is initially stabilized, the auxiliary unit will stop working, and the main unit will maintain the temperature drop and stability. If the refrigerant of the main engine group leaks, the cooling effect of the main engine group will be reduced. Since the two units work at the same time during the cooling process, the temperature will be stable, but the indicated cooling rate will decrease.
In the temperature holding phase, once the auxiliary unit stops working and the main unit has no cooling effect, the air temperature in the high low temperature test chamber will rise slowly. When the temperature rises to a certain level, the control system will start the auxiliary unit to cool down. And after reach a certain temperature, the unit will stop working. When this process repeats again and again, there might be a failure phenomenon that the auxiliary unit can't help anymore, and the low temperature can't be realized again.
So far, it has been confirmed that the cause of the failure that the low temperature cannot be maintained is the refrigerant leakage of the main refrigeration unit.
Check for leaks in the refrigeration system of the high low temperature test chamber. Combine leak detector and soapy water to check where the leak is. If the valve stem of the hot gas bypass solenoid valve is cracked, replace it. If the leaking is in other places, use oxygen welding to repair the leak point, and then refill the system with fluorine, then the system operation should be normal again.