You had better start finding and buying all the inefficient 134 A that
you can find if this is the way you choose to go with your AC system's.

Dupont, and one other company that makes the alternative freon's patent
rights run out in two years, and currently the price for the 134A is
between 350.00 and $475.00 per 30 lbs. bottle.

If you can locate it at Walmart, K-Mart for on the cheap, jump on it.

It won't be for long.

Mineral oil is used in R-12, R-12A systems.
Ester or PAG oil is used in the 134 charged sytems.