What is the symptom of a refrigeration system when the compressor loses oil due to leaking joints or fittings on the crankcase?

When a refrigeration system's compressor loses oil due to leaking joints or fittings on the crankcase, the primary symptom is the presence of oil around the compressor. This leakage occurs because the oil is essential for lubricating the moving parts inside the compressor. If the oil level decreases due to leaks, it will not be contained properly, leading to visible oil accumulation outside the compressor unit.

The leakage can also lead to other issues, such as reduced efficiency and increased risk of compressor damage. Identifying oil around the compressor is crucial for maintenance, as it indicates that there is a problem that needs to be addressed to ensure the longevity and proper functioning of the refrigeration system.

The other options represent different symptoms or conditions that may arise in a refrigeration system but are not directly indicative of oil loss from the compressor. For instance, bubbles in the sight glass relate to refrigerant issues, while water temperature discrepancies and valve statuses pertain to cooling efficiency and system operation, not specifically to oil leakage.