What are the reasons for the slow cooling of the constant temperature and humidity test chamber?

Under normal circumstances, the constant temperature and humidity test chamber will cool down to the corresponding value in accordance with the set time range, but because the equipment is used for too long, or improper operation, the temperature and humidity test chamber will slow down. Now how to solve this problem, the technical discussion is carried out.

Reason one:

1. Because the temperature cannot be maintained, observe whether the refrigeration compressor can be started during the operation of the test chamber. The compressor can be started during the operation of the environmental test equipment, indicating that the electrical circuit from the main power supply to the 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. Firstly, the exhaust and inspiratory pressures of the low-temperature (R23) compressor of the two refrigeration units are both lower than the normal values, and the inspiratory pressure is in the evacuated state, indicating that the refrigeration dose of the main refrigeration unit is insufficient.

3. Touch the exhaust pipe and suction pipe of the R23 compressor of the host unit by hand. It is found that the temperature of the exhaust pipe is not high, and the temperature of the suction pipe is not low (not frosted), which also indicates the lack of R23 refrigerant in the host unit.

Reason two:

1. The failure cause is not determined, and the failure cause is further confirmed by combining with the control process of the test chamber. The test chamber has two sets of refrigeration units.

2. One is the main unit and the other is the auxiliary unit. When the cooling rate is high, the two sets of units work simultaneously. After the temperature stabilizes initially, the auxiliary unit stops working and the host unit maintains the temperature stability. If the R23 of the host unit leaks, the cooling effect of the host unit will be small. Because the two units work at the same time in the cooling process, there is no temperature instability phenomenon, indicating that the cooling rate decreases. In the temperature maintenance stage, once the auxiliary unit stops working, the host unit has no refrigeration effect, the air in the test chamber will rise slowly, when the temperature rises to a certain degree, the control system will start the auxiliary unit to cool down, the temperature drops to the set value (-55℃) near, and then the auxiliary unit stops working, so repeatedly, there will be a fault phenomenon.

So far, it has been confirmed that the cause of the production failure is the leakage of refrigerant R23 from the low temperature (R23) stage unit of the host unit. Check the leakage of the refrigeration system, check with the leak detector and soapy water method, found that a hot gas bypass solenoid valve stem crack about 1cm. Replace the solenoid valve, refill the system with fluorine, and the system runs normally. As can be seen above, the analysis and judgment of the fault phenomenon is basically easy to difficult, first "outside" after "inside", first "electrical" after "refrigeration" vein for analysis and judgment, familiar with and understand the principle of the test chamber and working process is the basis of fault analysis and judgment.