In my case, I replaced the receiver/dryer (was told this was a good idea
as the old one would be contaminated with the wrong oil), about $60, and
another $125 for a local A/C & R guy to remove, drain and clean the
inside of the compressor, flush the system, evacuate it and recharge it
with R134a.  It worked all last summer and retained its charge over the
winter.

Mike
'85 Westy