first, why are you converting? leak? system not cooling? you need to solve those problems first. i just converted my system to R-134a, and it was pretty simple. i looked at the freeze 12 stuff, its 90% 134a and 10% some other refrigerant, something like R-142b. mixing refrigerants isnt a good idea, as they have different weights and will circulate differently, and the 134 wont circulate the oil. it costs about 30 bucks for a new reciever/drier, and if you have a leak, 10 bucks for the o-rings. 35 i paid for the conversion kit. change the oil to ester oil and you should be fine. mine works great, i get about a 25 degree drop in temps. i wouldnt keep the r-12. its the best refrigerant ever made, however you need a license to get it as stated above, you have to get it from an HVAC supplier, and its EXPENSIVE. youll also need a manifold gauge set that connects to r-12 systems, the only place that sells em is HVAC suppliers or ackits.com. id go with the 134a conversion if i were you. my 2 cents.