As for leak, If it is a Split Aircon - the answer is "YES"x9200 wrote:One more technical question: if the aircon is not used, can the gas still leak out? I am basically asking if there is any shut off valve between the compressor and the piping.

Shut off ? Nope, Don't remember that either. And anyway the outdoor units are not meant to be user serviceable, so I doubt anybody added that in the system.