Ac R-12 To 134a Conversion

I wish to convert my 89 caprice to 134a.
I have a mechanic bud who has done this conversion with the inexpensive retrofit kits that are available at the local parts store.
He says he has yet to have one come back.
I realize the correct way to do this is to flush entire system and change orifice and drier and comp oil.

My question is, how long can i expect this type of conversion to last verses the more thorough conversion?

Thanks for the help

Al

converted my 92 gran marquis over 7 years ago, still ice cold. just good flush, pay attention to pressures and stay away for sealants.

but if your unlucky, as i was, i went to a mechanic who quoted me $2000 to get my ac fixed the proper way.
the thing about recharging with the newer stuff is that its molecules are physically different (heavier and smaller i think, but dont quote me here).
it will last a while, but depending on the condition of your seals, condenser, compressor, and mess of hoses, it could possibly leak out within a matter of months.

for now, i use the good old "four square" air conditioning method.

what i'd suggest doing if you wanted to fix it correctly is to go on the assumption that most cars have working A/C, even after the car is dead.
go to junkyards and slowly start aquiring parts that are compatible with the newer A/C refrigirant.
by the time your retrofit kit wears out, you should have enough parts to put together your own A/C system.