I have a tank of 401 and a friend with a 91 pontiac that has no 12 left in it. From what ive read 401 can be used as a replacement for 12 systems, but does this apply with car a/c systems as well?? Any possible problems with switching to this refrigerant? And can it be just dropped in, or do i have to pull a vacuum on the system first. Any problems with performance in the long run as well?

*I did a little search on this, and couldnt find much, so sorry if this toipic has been discused before. Also, ive only been in the hvac field for 3 years now, so if any ignorance is spotted above, please excuse it, im just trying to learn. Thanks*