In which situation would you suspect moisture in an evacuated system?

When pressure starts to rise after reaching 500 microns, it indicates the potential presence of moisture in an evacuated refrigeration system. A steady vacuum below this level (typically 500 microns or lower) suggests that the system is effectively sealed and free of contaminants, including moisture. However, if the pressure begins to increase after achieving that desired vacuum level, it suggests that there might be moisture present. This moisture can vaporize and contribute to the pressure rise, indicating that the system has not been properly evacuated or that moisture intrusion has occurred.

In contrast, a system that maintains a stable vacuum would imply that it is likely sealed well, and the oil being clean and clear is a good sign of system health. Maintaining the vacuum for several hours also typically indicates that the system is functioning appropriately without significant issues such as moisture ingress. Therefore, the scenario where the pressure rises after reaching 500 microns is the clearest indicator of potential moisture problems within the system.