According to the U.S. EPA you should routinely inspect your AC systems, not just for mould, but also for moisture. Look at the drain and condensate pans to make sure they are draining properly. If they are plugged, the moisture that accumulates will become a mould factory.
Ensure that all AC ducts and system components such as air handlers, blowers and plenums etc are free of any moisture. If, despite regularly inspecting your system, you are experiencing issues (mould starts to grow in as little as 48 hours), you should consider a MouldGone treatment, using proven Green or chemical solutions.