I took my pick-up to a mechanic to get air system recharged, the mechanic put 134a in my r12 system. I did not realize until a few days later when the air would no longer cool, I took it to another mechanic and he said because of nothing being converted and the r12 still in the system I was going to have to replace my whole system now, is this true and if so should the first mechanic be responsible for the damages?
Replacement. Yes. The R134a is more corrosive to a system than R12. It attracts water. It uses PAG oil vs mineral oil for R12. If you never had a conversion from R12 to R134a, you should have screw type access ports on the suction line and discharge line of the compressor. A retrofit kit would have quick diconnect ports that screw onto the original threaded ports. The mechanic that charged your system probably should have been aware of that since it is a major difference.