Analysis of high and low temperature test chamber failure

1) The high and low temperature test chamber can be overcooled, indicating that the external factor cooling water can be eliminated.

2) Since the temperature is not maintained, observe whether the refrigeration compressor can be started during the operation of the test box, and the compressor can be started during the operation of the test box, indicating that the electrical circuit from the main power supply to each compressor is normal, the electrical system There is no problem in terms of aspect.

3) There is no problem with the electrical system and continue to check the refrigeration system. Firstly, the exhaust and suction pressures of the low-temperature (R23) compressors of the two groups of refrigeration units are lower than the normal values, and the suction pressure is evacuated, indicating that the refrigerant capacity of the main refrigeration unit is insufficient. Touching the exhaust and suction lines of the R23 compressor of the main unit by hand, it is found that the temperature of the exhaust line is not high, and the temperature of the suction line is not low (not frosted), which also indicates the R23 of the host group. Lack of refrigerant and leakage of fluorine in the system.

4) The cause of the failure has not been determined, and the cause of the failure is further confirmed in conjunction with the control process of the test box, which has two sets of refrigeration units. One is the main unit and the other is the auxiliary unit. When the cooling rate is large, the two sets of units work at the same time. In the initial stage of the temperature maintenance stage, the two units still work at the same time. When the temperature is initially stabilized, the auxiliary unit stops working, and the host group maintains the temperature stability. If the host group R23 leaks, the cooling effect of the host group will be small. Because the two units work at the same time during the cooling process, there is no temperature stability, and the cooling rate is indicated to decrease. In the temperature maintenance phase, once the auxiliary unit stops working, the main unit has no cooling effect, and the air in the test box will rise slowly. 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 setting. After the fixed value (-55 °C), the auxiliary unit stops working again. If it is repeated, the fault phenomenon shown in Figure 3 will appear. At this point, the cause of the production failure has been confirmed to be that the refrigerant R23 of the low temperature (R23) stage unit of the main unit leaks.

5) Checking the refrigeration system, using a combination of a leak detector and soapy water, found that the stem of a hot gas bypass solenoid valve cracked a slit of about 1 cm. Replace the solenoid valve, refill the system with fluorine, and the system is operating normally. As can be seen from the above, the analysis and judgment of the fault phenomenon is basically easy and difficult. First, the "outside" and "inside", first "electrical" and then "refrigeration" are analyzed and judged, familiar and Understanding the principle and working process of the test chamber is the basis for analyzing faults to determine faults.