Two types of R 134A oils are used. PAG oil is synthetic, and used in new
systems. Ester oil is compatible with the mineral oil based oil in an R 12
system. Ester oil is used in retrofit conversions. Using PAG oil in an
Ester based, or mineral oil based system * will *
cause problems. Beware of
" top up kits " "leak sealers "and other booster products, most contain PAG
oil, and will damage an Ester based system.