Driving Tip: Scan Your Gauges!
We just completed a 1000 mile round trip to Nac and back. Our old coach ran flawlessly the whole way, with only one mechanical "incident", which was indirectly my fault. Here's what happened. We're cruising down I-20 on the return leg, everything is fine. I scan of my gauges, and see the "2-needle" air pressure gauge is pegged out at 150 psig! 
Pulled off at the next exit, and parked in a empty lot. Left engine running as I tried to think what would cause this high air pressure reading. By "fanning" the brake pedal I could reduce the pressure to more normal readings, but it immediately started climbing again. Decided it must be the D2 governor, so opened engine hatch to take a look. Problem was immediately obvious...
Not too long ago I installed a air pressure gauge in the engine compartment so I could monitor the "wet tank" air pressure. It has been working fine. The gauge came with plastic (poly?) tubing to connect to air source. I tapped into a unused port on the D2 governor which "sees" wet tank pressure, installed a needle valve, and ran the tubing to the gauge. (see photo below) The plastic tubing was obviously a poor choice, because it had softened from engine compartment heat, and popped off the back of the gauge. The open-ended hose was keeping the D2 from reading the wet tank pressure, so it did not know when to unload the air compressor. I "assume" the relief valve on the wet tank went into action, and started venting the excess pressure from the tank, holding system pressure at 150 psig.
I closed the little needle valve, and the D2 was back in operation. The air compressor unloaded, and dash air gauge reading dropped back to normal range. I have detected no adverse affects from the temporary high system air pressure.
The moral to this story: Scan Your Gauges. Experienced drivers do this automatically, but there are many 1st time coach owners on this forum (myself included). We may get so caught up in the complexity of driving, or so entranced by the scenery out the front window, that we forget to watch the engine gauges. There is no audible alarm or dash warning light for "High Air Pressure", so we can't depend on that crutch. Get in the habit of sweeping your eyes over the gauges every few minutes - look for anomalous readings. Once your brain becomes accustomed to what is "normal", any deviation will immediately jump out at you.
Topic: Driving Tip: Scan Your Gauges!