1. Since the temperature of the high and low temperature test chamber cannot be maintained, observe whether the refrigeration compressor can be started during the operation of the test chamber, and the compressor can be started during the operation of the environmental test equipment. It means that the electrical circuit from the main power supply to each compressor is normal, and there is no problem with the electrical system.
2. There is no problem with the electrical system, continue to check the refrigeration system. First, check that the exhaust and suction pressures of the low-temperature (R23) stage compressors of the two sets of refrigeration units are lower than the normal values, and the suction pressure is in an evacuated state, indicating that the amount of refrigerant in the main refrigeration unit is insufficient.
3. Touch the exhaust and suction pipelines of the R23 compressor of the main engine group by hand, and find that the temperature of the exhaust pipeline is not high, and the temperature of the suction pipeline is not low (not frosted). This also explains the lack of R23 refrigerant in the main engine group.
1. The cause of the failure has not been determined, and the cause of the failure is further confirmed in combination with the control process of the test box. The test box has two sets of refrigeration units.
2. One is the main unit and the other is the auxiliary unit. When the cooling rate is large, the two groups of units work at the same time. In the early stage of temperature maintenance, the two groups of units still work at the same time. When the temperature is initially stabilized, the auxiliary unit stops working, and the main unit maintains the 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 phenomenon that the temperature cannot be stabilized, but the cooling rate is only reduced.
In the temperature maintenance stage, once the auxiliary unit stops working and the main unit has no cooling effect, the air in the high and low temperature 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 reduce the temperature. to near the set value (-55°C), and then the auxiliary unit stops working again, and so on.
So far, it has been confirmed that the cause of the production failure is the refrigerant R23 leakage of the low temperature (R23) level unit of the main unit. The refrigeration system was checked for leaks by a combination of leak detector and soapy water. It was found that the valve stem of a hot gas bypass solenoid valve was cracked with a slit of about 1cm. Replace the solenoid valve, recharge the system with fluorine, and the system runs normally.
As can be seen from the above, the analysis and judgment of the fault phenomenon is basically carried out in the order from easy to difficult, from outside to inside, first electric and then cooling. Familiarity with and understanding of the working principle and process of the high and low temperature test chamber is the basis for analyzing faults and judging faults.