Compressor won't fill with air

SOURCE: Hitachi EC12 Compressor- weird hum

The burst of air you hear as the compressor shuts off is the cylinder unloading so it will not have to restart against a high pressure load. If the unloader is electrical it would explain the hum that you hear. This could be a normal function.

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: My EC12 builds up pressure, but then releases all but about 10 psi.

The non-return valve is sticking and it's an easy fix. First, for safety, unplug the electric power to the unit and release any pressure in the tanks. Then unscrew the cap of the non-return valve (between the compressor and the tanks). Inside you should find a tapered rubber plug which is probably sticking in the valve housing. Sand down the diameter of the large end of the plug, being careful not to damage the flat face at the narrow end (which is the sealing surface). For sanding try 400 or 600 grade wet-or-dry paper and sand until the plug just moves freely in the housing. Reassemble and the compressor should work. Incidentally it's an oil-type unit, and quite durable. Make sure it has enough oil.

SOURCE: pressure switch out of adjustment

Before you adjust the perssure switch, make sure that the intank check valve is not leaking pressure back to the pressure switch after it cuts off at 140psi. The check valve should hold pressure at 140psi. Follow the discharge airline to the tank to find the checkvalve (either chrome or brass with large cap). To check for leaking valve, run compressor till shut-off at 140, then unplug the compressor from wall and remove the 1/4 air fitting at the checkvalve and check for leak. If leaking, replace valve and leave the pressure switch at present setting. You should be good to go. Good Luck with your repair and email if you have questions.

SOURCE: compressor runs fine builds up pressure then will

PRESSURE SWITCH IS BAD. NOT ADJUSTED CORRECTLY, POINTS ARE STUCK/WELDED TOGETHER OR THE NIPPLE UNDER IT IS CLOGGED. DRAIN PRESSURE AND REMOVE PRESSURE SWITCH. KNOW YOUR UNITS PSI AND TAKE THE SWITCH WITH YOU TO MATCH. IF YOU WANT TO INVESTIGATE FURTHER BEFORE YOU BUY, LOOK IN THE SIDE OF THE SWITCH AND YOU WILL SEE THE POINTS. THEY SHOULD BE TOUCHING WHEN ITS SUPPOSED TO RUN AND SEPERATED WHEN ITS SUPPOSED TO CUT OFF. HOPE THIS HELPS, JODY