Your car will never cool as well with R134a.
Besides, refrigerant is the cheapest part of your cooling system anyway.
Stevebfl has posted a lot about a/c issues, and here is a good post he wrote replying to guy who is considering converting to R134a:
"As I have pointed out many times the R12 in your A/C is still the cheapest part of it. To settle for crummy A/C to save money on the cheapest part there is poor economics.
I'm sorry but I would have to say that someone who has settled for no A/C for four years is a poor judge of whether it works as well. I have done over a thousand retrofits and still do a number every week. I give a customer what they ask for. Some I spend the time telling them the way it is. Some think this means I'm selling something. They get what they ask for.
The hardest part of being a competent tech is getting people to listen to you.
I'd love to see this car in a year or two. How in H*** can a tech tell that a system is good if it doesn't work. Or did you just turn it off for four years on bad advice. Unless there is no refrigerant in the system WHY would one change the refrigerant?? If there is no refrigerant whats going to keep that new stuff in. R134a leaks about 4 times as easy as R12. It will definitely find a way out of the compressor in a couple years unless it is new now."
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".