Who is responsible for mould from central air conditioning vents in strata buildings?

Responsibility here could be affected by a number of different factors. Principally, the type of scheme and the by-laws for the site. For the type of scheme, it is most likely to be a building format plan, although you should check this to be sure. If that is the case, and as per the BCCM website, then the body corporate is responsible for:

• utility infrastructure (like equipment, pipes and wiring) that is on common property, or in a boundary structure, or services more than 1 lot.

While the lot owner is responsible for:

• utility infrastructure (like equipment, pipes and wiring) that is within the boundaries of the lot and only services that lot; and
• utility infrastructure (including equipment and associated wiring and pipes) that is on common property, if it only services that lot and is a hot water system, washing machine, clothes dryer, air-conditioner or similar equipment.

It depends on the setup, but it’s quite possible that a part of the system serves only your lot and would be the owner's responsibility.

The by-laws for your site may well also ascribe responsibility for the upkeep of the system in one way or another so these should be checked. You can ask your body corporate manager for a copy of the by-laws and they can also assist with helping you identify if the issue is owners or body corporate responsibility.

Otherwise, mould issues are a common source of dispute as it is often very difficult to identify the cause or the resolution. You may need to engage a mould specialist to advise on this... If you think there is going to be a difference of opinion about the responsibility then it is best to make sure you have evidence to present in support of your position first. If you can make a reasonable case then you should get a reasonable dialogue. What you want to avoid is a situation where you say to the body corporate that a matter is their responsibility without having any evidence of this. In that scenario, the body corporate can simply reply that it isn’t and the subsequent impasse can be quite difficult to get out of.