AC Voltage: Wild Reading: phase-neutral & neutral-ground (240V/120V)
After searching the manual, I can confirm /u/jasen's suspicion of a communication wire, thus explaining the floating value. I probably should have checked the manual first, but I suspect this is similar for all brands.

https://portal.fujitsugeneral.com/files/catalog/files/HFI%20Install%20Guide8.pdf



http://www.fujitsuklime.com/wf-doc/fujitsu-klima-uredjaj-zidni-inverter-asyg09leca-installation-manual.pdf