What is procedure for upgrading to the newer type gas. Can you add the new gas to a older system R-12 without problems?

 

You can not mix R12 with the later R134A.

Are you sure that the system is R12? A retrofit kit for conversion from R12 to R134A was brought out by Volvo but the instructions I have for fitting the kit relate to vehicles from 1975 to 1990.