You'll probably find what you're looking for on the ARC website
ARCtick Homepage
This covers license requirements for handling greenhouse gases. I think its the "Office of Fair Trading" which issues licenses.
The other thing to consider is an electrical license. If you intend to install aircon then you'll need a full electrical license which will require a proven electrical apprenticeship. If you're servicing then you might get away with a restricted electrical license by doing a NREL course (National Ristricted Electrical) which is approx 1 year part time (night school). This permits you to disconnect/reconnect up to 600V.
Many people use the buddy system whereby you get your sparky mate in to connect to mains for you to get around the need for a full license.