good deal, yes adding refrigerant to top off the system can get you by for a while i guess. As long as it is working but remember, if it has a leak that will slowly go away and the efficency will fall off again.
if it does you will have to find out where the leak is by doing the evacuation and vacuum the system to verify if a leak is there.
If you can get hold of a good gas sniffer you can use that to detect where the leak is while the system is charged up, if a leak is there the sniffer will find it.