The diesel model 124's got 134 in '92.

Yes if the system is designed originally for 134 there is no reason that it won't cool as well or better. The 124 cars that came originally with R12 will NOT cool as well with 134. I fully expect that if you could find the condensor, aux fan and all necessary components from a later 134 equipped car, you could make it work as well as Paul's.

Before you do that, however, let's do some very simple math. I would guess that to change condensor and all associated parts assuming you perform the labor yourself would cost a bare minimum of $300 if you found what you need in the salvage yard and I think that is a LOW number. Then you need to fix whatever leak or other problem you may have regardless of refrigerant choice.

Okay, now, R12 can be had for $15 to $25 a can on ebay and it will cost you $15 to take the online test to get your 609 certificate to buy it. You would probably need only three cans for a 124, but let's say you need 4. Four cans at $25 is $100.

So you're going to spend $300, so you can save about $80 on refrigerant. I'm an older fellow and learned my math before what was called "New Math" came along. But, I fully expect that even with "New Math" you will find changing to 134 will cost an extra $220.

R12 is the least expensive component in your air conditioner. Repair what needs repairing, charge with R12 and enjoy being cool. It absolutely blows me away to see some of the incredible trouble and expense people go through to save $50 or $75 on refrigerant. It's like they refuse to do the simple math that is involved.

Good luck,