My ec12 runs for about 5 to 10 seconds then pops the circuit breaker

if you replaced capacitor exactly like it was remove and no wires switched you have a bad motor.

not necessarily it could be the start or run capacitor.

The breaker may be too small. Check the amperage requirements against the breaker size.

does it run freely?as in not seem to be lugging from bad bearings in the motor shaft,then check the speed control board for a shorted triac/scr transistor

Hitachi EC12 Air Compressor Parts : MASTERTOOLREPAIR.COM

Here is a site that says:
1. Are the capacitors good? (They get the motor going).
2. If they are, replace the stator, ($245)

If you don't find a good solution there, I would try taking it to a local motor rebuilder.
Gary

I have the same compressor with the same problem. I have temporarily eliminated the thermal reset with a piece of 12 gauge hard wire and it runs just fine. However, I do want to replace it before the warm weather come to the north. I tested the draw at 15.5 amps and the reset was a 17 amp. I am told by someone with superior electrical background that I need to install a 20 amp thermal reset in it's place. I have found that mine runs best when plugged directly into a 20 amp circuit and when using an extention cord I have a 10 guage cord that will carry the load needed to run the EC12. I also have changed to 100% synthetic oil.

hi there, in that case totally busted,there are motor protection should be checked if this are open. 1.check the source of current on circuit breaker using multi tester.if there is source or voltage supply.if nothing voltage supply reset breaker. 2.if current is available on circuit breaker check the overload protection relay if there is reset over load protection.try to power on. 3.check the pressure switch if open,it always normally close meaning the contact-or is closed if busted,replace pressure switch. 4.if still not work pull out motor and check this to electric motor service center. 5.check also the mechanical parts by cracking flywheel pulley of the compressor.if no rotation on flywheel pulley have check on this.if no motion it affects the motor protection. fix my rate and have a nice day thanks a lot.

does the breaker pop with an empty tank?
if so then you need to see if the unit turns free,try running the m/c disconnected from the pump unit,my guess is that your drive motor bearings or internal windings are at fault
hope this helps regards ian

There should be a pressure switch adjustment under the cover of the switch remove the cover and reset.

I have seen circuit breakers trip at a lower amperage. It seems that they are weak. Generally circuit breakers run with 80% load with no problem, in your case 24 amps. I would replace the circuit breaker.