What could cause a drop in vacuum inside the suction piping from 0.75 inches to 0.2 inches months after installation?

A significant drop in vacuum within the suction piping, particularly from 0.75 inches to 0.2 inches, indicates a problem in the system that can challenge its functionality. One plausible cause for this drop is an obstruction within the discharge pipe.

An obstruction can restrict airflow, which in turn affects the suction pressure within the system. As air struggles to move through the partially blocked discharge pipe, it creates a greater resistance, leading to a reduction in vacuum. This scenario suggests that the system is not operating optimally and indeed points towards an issue that needs to be investigated and resolved.

The other options, while possible concerns in different contexts, do not directly correlate with the described drop in vacuum. The fan being turned off would result in a complete loss of vacuum, and if the system were operating correctly, one would expect the vacuum to remain stable rather than drop significantly. Excess water in the piping could lead to other issues, but it would more typically create pressure changes rather than the described drop in vacuum specifically. Thus, an obstruction in the discharge pipe is the most logical explanation for the observed decrease in vacuum.