More data reported on R134a retrofits in this month's issue of 
"Automotive Engineering."  One article by Sanden Corp (compressor
supplier) and another one by ICI folks.  The Sanden article is new
data, but the ICI article is a shorter version of the paper they
gave at SAE Congress last month (SAE 940599).

The Sanden results seems to bolster the growing data that R12 to R134a
retrofits may not be as horrible as originally feared.  Sanden gives
a recommended procedure which has several options including:

   Drain as much mineral oil as possible (flush is optional).

   Add new PAG oil (theirs, of course).

   Replace any disturbed seals with H-NBR rubber.

   Replace receiver/drier with XH-7 or XH-9 (in expansion valve systems).
   In previously damaged CCOT systems, replace the receiver/drier after 
   running with a filter.

The more drastic measures such as new expansion valve, new compressor, 
new condensor or new vapor-barrier rubber hoses were considered optional
and depended on existing state of system.  

They also indicated that there is some empirical data to support that
compressors previously run with R12 may have better durability than
new compressors designed for R134a.

There is also a new SAE Recommended Practice (J1661) on retrofitting
procedures and methods.  I have not yet received my 1994 SAE Handbooks,
so I don't know if it is in there, or must be ordered as a separate
document.

Interesting stuff.  I'm beginning to wonder whether I should just jump
off the clift and retro my 1979 car now (and save my 30-lb R12 tank for
later use, if it doesn't work); or wait until I finally use up that freon
(around 2003 in the worst-case)?

mark
================================================
Article: 51026 of rec.autos.tech
>From: mark@wdc.sps.mot.com (Mark Shaw)