Got a '87 with a "sorta" working ac.  I got some Freeze -12 but wondering if it will mix with whatever old R12 is in the system or should I evacuate the system and start from scratch?  I would like to just get something in it to help with cooling car but I don't want to wreck anything.  I have learned alot about vanagons from this forum.  Thanks for the comments.  R, Steve