A series of reasons for detecting the slow temperature change rate of high and low temperature test chamber

Under normal circumstances, the high and low temperature test chamber will cool down to the corresponding value according to the set time and temperature, but it is likely that the temperature of the high and low temperature test chamber will become slow due to the equipment being used for too long or improper operation. On this issue, the frequency instrument conducts technical discussions to answer your questions:
1. 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 environmental test equipment, indicating that the electrical circuit from the main power supply to each compressor is normal, and there is no problem in the electrical system.
2. There is no problem with the electrical system, continue to check the refrigeration system. First check the discharge and suction pressures of the low-temperature (R23) compressors of the two groups of refrigeration units are lower than normal, and the suction pressure is evacuated, indicating that the main refrigeration unit has insufficient refrigerant quantity.
3. Touch the exhaust and suction lines of the main unit R23 compressor 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), which also shows that the main unit The lack of R23 refrigerant.


4. The cause of the failure is not 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. 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. At the beginning of the temperature maintenance stage, the two groups of units still work at the same time. After the temperature stabilizes initially, 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 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 set value, and then the auxiliary unit stops working, so repeatedly, there will be a malfunction.
Based on the above, it has been confirmed that the cause of the failure is leakage of refrigerant R23 of the low-temperature (R23) class unit of the main engine unit. Check the refrigeration system and use a combination of leak detector and soapy water to find that the stem of the hot gas bypass solenoid valve has cracked about 1cm. Replace the solenoid valve and refill the system with fluoride.

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