1) The high and low temperature test chamber can experience overcooling, which suggests that external cooling water may not be the primary factor. This indicates a potential issue within the internal system rather than an external influence. 2) Since the temperature is not being maintained properly, it's important to check whether the refrigeration compressor starts during the operation of the test box. If the compressor does start, it implies that the electrical circuit from the main power supply to the compressor is functioning correctly, and there are no major issues with the electrical system. 3) With the electrical system confirmed as normal, the next step is to inspect the refrigeration system. It was observed that the discharge and suction pressures of the low-temperature (R23) compressors in both refrigeration units are below normal levels. Additionally, the suction pressure is being evacuated, indicating that the refrigerant charge in the main unit is insufficient. By touching the discharge and suction lines of the R23 compressor, it was found that the discharge line is not hot and the suction line is not cold (not frosted), further confirming a lack of refrigerant and possible leakage in the system. 4) To better understand the root cause, the control process of the test box was analyzed. The system has two refrigeration units: a main unit and an auxiliary unit. During periods of high cooling demand, both units operate simultaneously. In the early stage of temperature stabilization, both units continue to run. Once the temperature stabilizes, the auxiliary unit stops, and the main unit maintains the set point. However, if the main unit’s R23 refrigerant leaks, its cooling capacity will be reduced. As both units run together during the cooling phase, the temperature may not stabilize, leading to a slower cooling rate. During the temperature maintenance phase, when the auxiliary unit turns off, the main unit cannot maintain the temperature, causing the internal temperature to rise slowly. When it reaches a certain threshold, the control system restarts the auxiliary unit to cool down again. This cycle repeats, resulting in the fault condition shown in Figure 3. After thorough investigation, it was determined that the failure originated from a refrigerant leak in the R23 stage of the main unit. 5) Further inspection of the refrigeration system revealed a small crack in the stem of a hot gas bypass solenoid valve. Using a leak detector and soapy water, the leak was confirmed. The faulty solenoid valve was replaced, and the system was recharged with refrigerant. After these repairs, the system operated normally. From this experience, it is clear that identifying and resolving such faults requires a systematic approach. Starting with external factors, then moving to the electrical system, and finally analyzing the refrigeration components, is essential. A solid understanding of the test box’s principle and operational process is crucial for accurate fault diagnosis and resolution.
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Analysis of high and low temperature test chamber failure