All A/C recharges really need to be done by a professional. If you have R12 now you have probably found only licensed HVAC people can buy it, and if you have R134a now it must be charged by weight, not by some bogus gauge stuck on a can.
No. A system uses either R12 or R134a, but not a mixture of both. Do not attempt this!
No. They're 2 different compounds. You have to bleed out the old to replace with the new. Then installing the new and different sized fittings.
NO NO NO NO
Evacuate and charge with one or the other(you didn't mention which system you have 134A or R12) But do not combine both refrigerants in the same system.
I'd say go for it, Your most likely going to screw this up anyway so whats the difference
