Those interested might want to take a look at
http://www.sanden.com/sanden/products/piston5.html
Seems Sanden has a modified 508 compressor designed for the 134a
refrigerant, model SD5H14. Seems that most of the changes have to do
with improved seals for the higher pressures of the R134a.

Apparently the first number of the compressor model indicate the number
of pistons in the compressor. Sanden claims that the '7' series will
have reduced vibration, reduced noise, and better performance.

see: http://www.sanden.com/sanden/products/piston7.html

Hope this helps the curious.

Todd
'88 Westy