hey I am also in the same situation, i heard it was pretty simple to DIY, but still dun understand it fully, i gonna have a buddy show me, maybe i can tell u then. I too got a 91 coupe, so if anyone else knows please enlighten us.
Thanks~db

 

If you have the R134 conversion done to your a/c it's very easy. You can buy a kit from AutoZone or anyshop like that. If you still have R12 I'm pretty sure you're gonna have to take it somewhere, b/c I don't think you can buy that type of freon... I may be wrong tho.

 

Yeah, most 1989-1990 240's my still have R12 systems in it cuz mine does. You need to evac any remaining R12 stuff in your tank. And you can't buy R12 freon by yourself too cuz you need a license and there's environmental issues with R12. Best suggestion is to have a shop evac and convert R12 system to R134a. Now with R134a will be much easier to refill.

Oh, make sure to get an oil charge, fittings, and hoses to go recharging.

 

If it's empty (no R12) you can probably just buy the conversion kit at the parts store for like $50. It has the adapters for the 134.