I got my compressor in the UPS on monday. I hooked it upto 85 PSI (I have a 20 CFM compressor). I filled my tank once and it worked fine....It shut off at 4000PSI

I turned the compressor on to fill the tank again before i went to work today.....It shut off at 3000 PSI for some reason. I turned the switch on and it blew the fuse. I changed the fuse and turned it on and it started to move......acted like it was under load (No tank connected to compressor) and then all of a sudden it stared to pin normal RPM again...........any ideas? The thing is brand new......and im running 85PSI