Replacing old multi-split in an apartment—how to deal with missing communication cables to the roof?

Peoples Republic of Victoria

Hey all. I need to replace a dead, 11-year-old multi-split system (1 outdoor unit on the apartment building roof, 2 indoor heads on a single level) in Melbourne. My installer checked it out and noted a massive hurdle: the existing wiring from the old system lacks the extra multi-core communication/interconnecting cables required by modern systems (which need 4-core wires per head to talk to the outdoor compressor). Because of finished plaster bulkheads, fire ratings, and concrete slabs, fishing brand-new cables up to the roof through internal walls is looking incredibly difficult. I know other units in my building have successfully upgraded, so there is a workaround. Before I chat with the Owners Corp, I wanted to ask:

For those who have replaced multi-splits in a mid-rise/high-rise apartment block, how did your installers run the new communication cables? External conduit on common property? Dropping it down an existing service/utility riser?

Are there any specific modern brands (Daikin, Mitsubishi, etc.) that have a retrofit tech allowing them to communicate over older, limited wiring configurations?

Should I be looking at a specialized commercial HVAC company rather than standard residential installers?

Posted Jun 17, 2026, 1:10 PM UTC