The reason most people are looking at alternatives is they can be purchased without a license/certification and can be easily added to the a/c system with existing tools used with R12. Topping off the system with R12 is costly since many places will tell you they can't fill your system without accounting for and "fixing" the leak. That might be a seal or two and when you get the final bill you are probably looking at $150 or more. The cost of alternatives is significantly less than that. I agree the best thing to do is use whatever refrigerant the system was designed for.

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