[Richard]

I would take my handy dandy solenoid valve isolator setup and install between the six pack and the outlet line to the left rear. For those who aren't familiar, it is simply a ball valve with guages on both sides. You install as I described, and depending on what the gauges do, you can figure out where you do and do not have air pressure.

You don't have a tag IIRC, so that rules out some issue with the tag dump raise valve not operating correctly.