What is the normal pressure of the wet tank. I think my main problem is that my M923A2 came with a relief valve rated for 65 psi which keeps discharging. It appears that this valve should have a rating over 100 psi, probably as high as 125. Is that correct
No. That is not correct.
Compressor builds air and sends it downstream. PPV engages once it sees 70psi (or therebouts). Once the PPV engages , air is sent to the governor and everything else on that side of the system (horn, wipers , other 'nonessential' equipment ).
If the PPV doesn't see 70psi, it doesn't send air to that side. The governor never sees pressure so never cuts flow. The air dryer doesn't purge. The horn and wipers don't work. Pressure continues to build. When pressure reaches 150psi the pressure relief valve opens. Driving at steady highway speed, the pressure relief valve will rhythmically open about every 10 seconds.
Question 1) what led you to believe the PPV wasn't working?
2) what led you to believe the governor needed replacing?
3) have you tampered with the manual valves?
4) what have you done to adjust the governor?
5) is the air compressor outlet line hot?
6) what happens when you disconnect the line between the governor and the unloader?