If it’s a eg split system unit that services your lot only, as seems to be the case, then in Victoria the OC Act states that the lot is responsible for its maintenance.
No OC Rule can change that.
It doesn’t matter that parts of the unit are sited on common property or that its plumbing and electrics pass though common or even other lot property (allowed by implied easements), it’s still a lot responsibility. Victoria is different to some other states/territories in this regard.
Repairs can sometimes be tricky and expensive. It depends on how it was installed. And the lot owner must repair any damage done to common property or another lot’s property.