I disassembled and reassembled the faulty transducer. Nothing visibly wrong but it must be the circuit board is fried. They say the NEMA case can be installed at any angle but what I found is that the hole in the conduit pipe threading where the electrical pigtail comes out is not watertight and leads directly to the circuit board. I don’t think that caused the failure in my case but it is worth point out for others that find this article.
I also tried switching to the second set of in/out ports thinking maybe one side is completely clogged – no dice. So I ordered a less expensive replacement (although the 900X is still readily available, I opted to try the 500X series). The mechanism is electromagnetic instead of a piezoelectric. It also wastes less air and has more known variables like the relief CFM rate. I hope I don’t like it too much and want to replace the remaining three 900X units!