r134a or freon

the refrigerant isn't that expensive ($30 -$40).but if the system has been open for awhile it should have a new drier and oil change. the most important thing is that it is clean and leak free. then it will need to be vaccuumed to remove all moisture and leak tested, then recharged. There are several replacement refrigerants available to replace the original R-12.R 134 is an HFC refrigerant and requires that 95% of the oil be changed to POE oil.This can be difficult to do and may take several oil chnges to get done(expensive).I've had good luck with 409A as a replacement and it will work fine with the oil already in the system (mineral oil).If you do not have the tools or experience to do a/c then it could cost you a few hundred dollars to have repaired. Shop around and get someone good to do the work, otherwise it may not work for long. good luck