If ammonia is seen venting from the top of the expansion tank, what does this indicate?

When ammonia is seen venting from the top of the expansion tank, it typically indicates that there is a problem with the system, specifically that ammonia and brine have mixed due to a failure in the evaporator tubes. In a properly functioning refrigeration system, the ammonia should remain contained and not mix with the brine. The venting of ammonia suggests there is a leak or an unintended pathway allowing the ammonia to escape, which is often symptomatic of tube failure. This could lead to reduced efficiency, operational hazards, and poses a risk of environmental contamination.

In contrast, the other scenarios do not accurately describe the situation. If the system were functioning normally, there would be no venting of ammonia observed. Similarly, low ammonia refrigerant levels are not indicated solely by venting from the expansion tank, as the venting is more about a failure in containment rather than simply a quantity issue. Normal pressure release would not typically involve ammonia venting into the environment, as this could indicate a malfunction rather than a standard operation. Therefore, the indication of mixed fluids is the most appropriate interpretation of the observed venting.