Sounds a bit weird to be honest. My old AS 186 didn’t have a reducing valve, so used to pulse annoyingly when in use because tank pressure was only controlled by the limit switch. Filled to about 25, then drained to about 5 before refilling. Maddening!
I may therefore not quite understand the problem. if I have got it wrong then ignore this….
As I understand the problem, the compressor tank fills according to the inbuilt limit switch and you then set the delivery pressure independently using a pressure reducing valve (PRV) fitted on the hose outlet? The air then bleeds out of the PRV until there is nothing left.
Perhaps there is therefore a fault with the pressure reducing valve or gauge? Do you set pressure with the
airbrush running? It may be that the gauge is inaccurate (even good ones are very unreliable) and what seems to be a setting of 15psi is actually zero. The pressure would then bleed out of the PRV. Peter’s could be the opposite…15 could be well above the actual limit switch pressure, so the compressor won’t start because the tank is already at pressure?
Just out of interest, have either of you drained the tank and PRV catch pots of condensate recently? Might just be moisture in the PRV or limit switch?