Has my unloader valve been blocked on purpose????

Just got a used year 2000 sip airstream 150lt 3 hp compressor needing attention. Done all the gaskets and valve plates etc and everything is going well but then it popped a fuse and I didn't think much of at the time but there's no pipe running from the pressure switch to check valve, although there is a blanked off port there. I imagine that's the reason it popped a fuse and I'm wondering if I should install a line to here from the unloader valve ( condor switch which it assume has an unloader built in ) or was my unit designed without one??? My last issue is the motors rest switch has been bypassed, should I leave it as it is or reconnect/replace? Jeff Gormley, N ireland