Is it possible to tell if the AC is R12 or R134, BESIDES the low/high side
fittings?

When I purchased my 88 Westy over a year ago, the previous owner (whom I've
found no reason not to trust), said the van had previously (by the prior
owner) been converted to R134.  But when I went to fill, I noticed that it
did not have the R134 low side fitting.

I contacted the seller, and he recalled that he thinks he filled it, and
then may have removed the fitting for use on another van.

So then I checked the high-side fitting, and that does not have the R134
fitting either.  Weird.

So, is there a way for me to tell what I have in there?  If not, what should
my next course of action be, assuming there's the possibility that R134 may
have been added to an R12 system?

Thanks,

James V
88 Westy