Is my Aircon Gone?

Hi guys, never really used my aircon since I got my car last year. When I turn it on I definitely notice an extra strain on the engine but the temperature coming out the vents doesnt seem to change at all. Has anyone else had this problem? I have heard that air-con systems need to be " re-gassed " from time to time, but Im not sure what this really means.
Any help would be appreciated.
DAN
Any help would be appreciated.
DAN