<<What should I flush my system with when changing from R12 to 134a?
I'll be installing a new dryer at that time.
Stan Wilder>>

I guess you don't need that wasted process Stan.
Just go ahead and drop the 134 into the mineral oil R-12 system.
You don't need to swap O-Rings, the dryer.
Evacuate?
Not needed.
Forget the Ester, or Pag oil.
Them AC engineer's were dummies.
It's just a marketing ploy so draw some more cash out of your pocket.

Take a stroll though the isles at Wal Mart.
look for the Miracle 134 AC conversion kit.

Or take a ride to Winn Dixie.
Look for the Jello display,.
It'll be doing the same thing to your AC system.
Might as well load up.