Compressor motor problems

[Sharpest]

I bought this compressor with a ****** Home Air Base compressor in a package deal off Craigslist. It was missing the pressure switch when I got it so I installed a switch, replaced the pressure relief line and retaped all the pipe joints. As you can see from the data plate, the motor that came on it is a Century "SPL" HP rated, 3400 rpm unit that is noted to draw 15 amps when wired for 110 volt. I plugged it alone in to a 20 amp circuit and it would start and run for 5 seconds or so before blowing the breaker. It is wired correctly and hasn't let any magic smoke or smells out so I don't know why the breaker is blowing. I had an OLD Century 3/4 HP 1700 RPM motor with the same case size laying around so I swapped them out. With the smaller 3400 rpm pulley on it the older motor works great and is the quietest compressor I've ever heard but it is really slow to fill the tank. If I can figure out how to fix the newer motor I'd like to reinstall it for the better performance but I don't know what's wrong with it. Any ideas? Here's a couple pics. Data place is the newer motor that is FUBAR.

 

[Hornman]

Could be that the motor is pulling more amps than rated. It would be good to put an ammeter on the motor on startup to see for sure. Your 20 amp breaker could be weak. Breakers are cheap, replace it with a new one. It also looks like the discharge of the compressor goes directly to the tank. If so, you are starting up with the compressor under full load, which is not good. Consider adding a pressure relief vent and check valve between the compressor and tank.

 

[G_P]

Looks like the unloader line goes to the check valve on the tank. As long as that is working correctly it is not starting under load.

 

[Sharpest]

Unloader line is routed in the factory configuration from the check valve at the tank to the switch itself.