Mate if the air con is off and its still sqeaking then its your power steering belt there is a tensioner located near the power steering pump it has a 12mm bolt on top of it and a 12mm bolt on the front of it. Loosen ( do not completly take out) the front bolt, then turn the top bolt clockwise to tension the belt ( prob 2 - 3 turns should do it) Once the belt has been tensioned then tighten up the front bolt to lock the tensioner in place. Squeak should be fixed

well actually it can be either the air con or the power steering/alternator belt..
as for turning air con on and off that will only prove if it is coming from within the air con compressor, a worn bearing will do that..
either way check the tension on all your belts first and go from there...

When the aircon is off the air con belt will still turn but it is spinning freely with no friction so it won't slip ( Squeak ) when you turn the air con on you engage the magnetic clutch which turns the internals of the compresser causing friction and if the belt is loose belt slipage. Yes a worn bearing will also cause noise but going on the fact his original post said that it sounded like The squeak was coming from a belt and that he only has around 100km on the car a compressor bearing would be pretty unlikely

fair call...
i got the impression that you were sayin the belt would miraculously stop moving when you turn the air con off...

just spray the timing belt crc should be fine.. if the belt is wet from water it can squeak