Replacement fo CO2 Bulk Tank refrigeration unit

[pabs_ref]

Good Day to all! I have this problem for a Coca-Cola
bottling plant. Hope i could have some of your advice
on this matter..The CO2 bulk tank holds 50 tons..
the existing refrigeration unit is Russel condensing unit
with a 10TR Copelametic Discuss Compressor and *****22...
The compressor recently failed...they management want
us to retrofit...either to 134a or R404a or some ozone friendly
refrigerant...
The CO2 unit was locally manufactured with the
evaporator inside...With a compressor replacement
with the same refrigerant there would be no problem.
With a different refrigerant .. let's say 134a, do i have to change
my condenser & evaporator coils?Do i have to increase or decrease
the capacity of the compressor?...any special retrofit procedures
to eliminate the mineral oil from the system, especially from the evaporator..
Any inputs from all of you guys will be appreciated... thanks in advance..