I think Saddlebum is on the right track. The compressor shows all the symptoms he mentioned. I have a 135 psi pop off valve that works properly. The unloader starts bleeding air off first on the bottom of the regulator and continues to do so till the tank is empty when the switch is turned off. With switch on it'll still continue leaking even after the motor kicks on & compressor builds pressure again, running continually at that point.
I'll check that one way valve tomorrow.
Thank all, Larry