I'm not sure I understand your situation. You said originally that your car was converted 5 years ago leading me to believe that it was properly converted at that time.
If that is the case and it is low on refrigerant, you should not have evacuate unless the system is COMPLETELY empty.
From your more recent post it sounds like maybe it was done without removing the R12, going through the complete procedure and then evacuating.
Which is it?
Have a great day,