Thanks for the advice and links, Wayne! As it happens, we already have
Nigel Calder's book, which we always pick up and pore over any time we
have a new mechanical or electrical problem. It's incredibly complete
and useful -- can't imagine how we (or any other creuisers) could do
without it. We definitely read the section on refrigeration, and
learned a bundle.

Unfortunately, that appears to be what got us into our current problem,
as Calder was (I guess) writing with R12 in mind. It's because of him
that we filled the system until the sight glass was full, and
apparently overcharged. Also, he gives a table for ambient temp vs.
refrigerant pressure for R12 but nothing for R134a -- and it turns out
you can't use his table for R134a, even as a SWAG.

We finally bought the gauges but didn't think a 220V vacuum pump was a
worthwhile investment as we'll be returning soon to the 110V world. If
we open the system, we have to borrow or rent somebody else's pump. We
judge compressor and return-line temps by feel -- in the former case,
if you can touch it without burning your fingers it's not too hot, and
in the latter if it's cold but not frosting it's not too cold.

Rob