First check whether the refrigeration compressor of the test box can be started during operation. If the compressor can be started during operation, it means that the electrical circuits from the main power supply to each compressor are normal, and there is no problem with the electrical system. When there is no problem with the electrical system, continue to check the refrigeration system. First check the two groups of refrigeration compressors. If the exhaust and suction pressures of the low-temperature (R23) compressor are lower than the normal value, and the suction pressure is in a vacuum state, this means that the refrigerant amount of the main refrigeration unit is obviously insufficient. Then touch the exhaust and suction pipelines of the R23 compressor of the main unit with your hand. If you find that the temperature of the exhaust pipeline is not high and the temperature of the suction pipeline is not low (no frost), this also means that the R23 refrigerant of the main unit is insufficient. One of the test boxes is the main unit and the other is the auxiliary unit. When the cooling rate is large, the two units work at the same time. In the early stage of temperature maintenance, the two units still work at the same time. When the temperature initially stabilizes, the auxiliary unit will stop working, and the main unit will maintain the cooling and stability of the temperature. If the R23 of the main unit leaks, the cooling effect of the main unit will be small. Since the two units work at the same time during the cooling process, there is no temperature stabilization phenomenon, and the indicated cooling rate is reduced. In the temperature maintenance stage, once the auxiliary unit stops working and the main unit has no cooling effect, the air temperature in the test box will slowly rise. When the temperature rises to a certain level, the control system will start the auxiliary unit to cool down, and then the auxiliary unit will stop working again. This will be repeated, and the low temperature will not be able to be maintained.

So far, it has been confirmed that the cause of the failure of the test box is the leakage of refrigerant R23 in the low temperature (R23) level unit of the main refrigeration unit.

Maintenance method of test box: Check the refrigeration system of the test box for leaks, and use a leak detector and soapy water to check the leak. If the valve stem of the hot gas bypass solenoid valve is cracked, replace the solenoid valve. If leaks are found in other places, use oxygen welding to repair the leaks, and then refill the system with fluorine. The system can resume normal operation.

From this, it can be seen that the analysis and judgment of the fault phenomenon that the test box cannot maintain low temperature is basically from easy to difficult, first outside and then inside, first electrical and then cooling. Familiarity and understanding of the principle and working process of the test box are the basis for analyzing and judging faults. Only by deeply understanding the working principle and working process of the test box can we quickly solve various problems that arise during the operation of the test box.