Two interesting papers at SAE conference this week about studies and
developments regards retrofiting HFC-134a to older R-12 systems.   

One is by Colmery, et al from ICI Klea involving a study of 8-10 vehicles
from a 200-vehicle fleet that was converted to HFC-134a.  Some systems were
just extract R-12, drain mineral oil, flush with R-12, fill with PAG oil and
HFC-134a. The only component actually changed out was usually the
accumulator/drier; but in some cases that was let as well.  

Bottom line, they are not seeing any adverse effects over a 2-year period
and have only seen a couple of compressor failures out of the 200-car fleet.
And there was some question as to whether these were newly created failures
or compressors that would have given up anyway.  No evidence of degradation
of the HFC-134a, the PAG oil or the dessicant from residual chlorine or
mineral oil in the system.  Also no deterioration in the rubber parts or
hoses.  Compressor wear was considered normal after the 2-year period.
The interesting drawback was that the dessicant was fully saturated after
the 2-year period in most cases, which would suggest a system evacuate
and fill with an exchange with a new accumulator every two years to maintain
performance.

Another paper by Yokoo, et al from Nissan covered a new lubricant for HFC-134a
retrofits. It is a PAG base oil with an antiwear additive (benzotriazole or BTA)
which they claim brings the PAG oil within the lubricity of mineral oil and it
is not affected by retained chlorides or water.  

Finally, Castrol is now marketing a retrofit oil called ICEMatic Retro 100
which is an polyol ester based oil claimed to be tolerant of residual CFC-12
and mineral oils.

The two SAE papers 940599 (Colmery, et al) and 940594 (Yokoo, et al) can be
obtained from the SAE (412) 776-4841 for $4.50 each.  Data on the Castrol
Oil may be obtained from Castrol.

All the above work appears directed at the swash-plate type compressors and
a casual conversation with the presenter of the ICI paper and the Castrol rep
indicates that the older piston-type (i.e. York or Tecumseh) compressors would
be less of a problem.  

Some may argue the validity of the above papers (and/or their motives) but
this type of progress is positive data, none the less.

Mark
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Article: 50673 of rec.autos.tech
>From: mark@wdc.sps.mot.com (Mark Shaw)