The summer is most gone and so is the need for AC but it sure was nice to
have earlier. Back when I had my '88 van, I dutifully switched my system
over to R-134a because R12 was going out and what little was available was
astronomical in cosy.  I changed the service fittings, purged the system,
then vacuumed the system, and added the appropriate amount of 134a. This
was in spring. By mid summer the refrigerant pressure had dropped and was
no longer cooling properly. I added 134a and brought it back up to speed.
By fall of the first year the pressure was back down. This was a
puzzlement. there was no sign of leakage any where. I didn't refill it as
cooler weather had set in but I knew the problem had to be solved by spring
when I had to service it again.

During the winter I stumbled across a discussion about molecule size of
various refrigerants and how their sized was affected by hose design. It
would seem that 134a has much smaller molecule size than R12, and
consequently the stuff over time would leak right through the old original
hoses. And the original hoses is what I had. While pondering this
situation I stumbled on a video of Dustaway keyboard and computer cleaner
being used as a refrigerant to service the AC SYSTEM. Supposedly the specs
were similar to R-12 at least in molecule size so there should be only
minimum leakage. It works great as a refrigerant cooling with the best of
them. and I haven't changed or added to the system for a couple of years.
You can find videos on Youtube about this. And if you decided to try it,
make sure your can says on it somewhere CAS 75-37-6