A/C fundamentals question....

[VTKidder]

All A/C gurus....

What parts of an A/C system are changed when a system goes from R12 to R134a? I'm not talking a retrofit, or recharge, I'm talking ordering a new A/C system, and ordering it as a 134a system. You hear all the time "I retrofitted the system to 134a, but it just doesn't blow as cold as the R12 did." R12 and R134a are different refridgerants, and thus would have different cooling properties. New A/C systems blow ICE cold, because they have had all of their parts designed around using the properties of R134a. Adding R134a to an R12 system obviously doesn't work as well. So my question is....what parts of the A/C system are designed around the properties of a refridgerant, and are different than an R12 system? If you ordered a full R12 and a full R134a system, what parts would be the same, and what parts would be different? I take it the compressor is, probably the condenser, expansion valve and some others. What's your understanding of the difference? Thanks.....

-adam