90 20V Quattro 1989 model Aircon

[Leon]

You should be able to see it on the connectors on the AC lines. Google
the R-12 and R-134 connectors and you should be able to see if it has
been already converted for the R134 refrigerant. Most stores sell only
the R134 as the older stuff is illegal now. Get a recharge kit that
has a gauge on it, that should tell you if there is still any pressure
within the system. Remember, only connect to the LOW side!
Air conditioning troubleshooting is hard without the proper tools, but
if your really lucky, it may just need a recharge...

Dave