Hello my first post

Anyone have any advice on detecting a leak on 3 pipe VRV sytem over 3 floors high with approx. 20 cassette units attached to it.

Tried UV dye and the usual soap solution
going out of my head trying to locate this leak
my next step is to split the piping into three parts. Seal the ends and pressure test each on seperately hoping to find it.
Anyone got any advice