not sure if this is the right place to post this but here goes. (if not, please move to the appropriate forum)

just got delivery of an AS186 air compressor and airbrush and i can't seem to get the regulator to set the working pressure to correct setting. it's got an auto shut-off for filling the air tank but i can't seem to get it to fill up and shut off at 20psi.

can anyone help?