Ohtooman has two issues that make his car a very poor candidate for a 134 conversion. First he is in Oklahoma, not a tropical climate, but certainly not known for chilly summers. Second he has a 123 MB. This car has a very marginal refrigeration capacity due to limited condensor size.

If he were willing to spring for a parallel flow condensor, then he might be able to make a 134 conversion cool adequately, BUT that would cost more than just using R12 and be done with it. R12 prices are coming down. I just bought a sealed, 30 pound cannister delivered to my door for $425 total cost. That's less than $15 per pound and I didn't even shop very hard. It probably could be had for less.

It has amazed me how much money I've seen people spend so that they can pay $5 per pound for refrigerant rather than $15. I only went to public school, but the math that they taught me just doesn't show this to be an economically feasible modification.

Have a great day,