psfred -
very useful advice.

Re evacuating the system/testing vacuum retention, is one of the venturi devices (as sold by ackits) sufficient? Supposed to develop 29in vaccuum. Another source insisted you need a pump good to 50 microns for proper results.

Re hoses again, from the Mastercool Auto AC Basic Service Manual, p 12,

"Because R-134a is composed of smaller molecules than R-12, the permeation of R-1341 through rubber hose is about double that of R-12, resulting in a faster loss of A/C charge. To correct this problem, nylon-lined or Nitrile Internal Barrier hoses are used. Internal barrier hoses use coupled hose connections instead of gear clamp fittings, which will not clamp the internal barrier hoses correctly...."

Just because this is published here doesn't mean it's correct, of course.

Now the blue mb high pressure hoses that I see on either side of the receiver/dryer have markings which may indicate they're ok for r-134 (I think the brand name is "nyl"-something), and they don't use gear clamp fittings, but I'm simply not sure that they're proper for r-134. I don't know what the recommendations are for a retrofit of this system.