How do I adjust the pressure on my hitachi ec12 which has no pressure regulator knob?

SOURCE: ec12 hard restart after drop in air pressure

It sounds like the air pressure assembly unit is not reading the pressure drop. some of these units have adjustments under the covers and be reset.

SOURCE: hitachi ec12 motor hums after drop in pressue

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

SOURCE: ec12 hitachi air compressor will not build

most likely the the reed valves are stuck or miss aligned. Worse case senerio your piston seal blew causing this not to build pressure. Read manual on how to disassemble head. to remove should be 4 bolts and your copper line, just be careful of the reed valve plates, they are thin steel that sit into the head. Put back the same way you took it apart.

SOURCE: do not have manual for hitachi ec12 air

You have to manually adjust the pressure regulator. Make sure drain is completely closed. The one thats on the bottom of the tanks

SOURCE: I got a used Hitachi ec12 compressor, it doesn't start.

1.Check the motor first. You can readily see if it's
burned or not. Run a megger test on the motor.
Test run the motor without the compressor.
2. If, it does not run, have it checked at the motor
rewinding shop.
3. Once it is okey, remount the motor, and start it up.