First of all, which sensor? If it is BOB-08882 or BOB-08883 (ACS712), STOP RIGHT NOW AND DISCONNECT IT. Spacings between tracks on that board and the ground plane are too close to safely use it on 220V (or 120V, for that matter). Using either board on line voltage may at best destroy your computer, and at worst be lethal. Yes, the chip is rated at 2.1kV isolation. The PCB design is far from that. I have sent them a comment asking them to put a safety note on the product pages.
If not that one, which is it and how is it connected to the Arduino and the fan?
I would switch to a non-invasive current sensor like SEN-11005. To step up the sensitivity, just pass the wire through the core multiple times.
/mike