What is the amount of R134a needed to fully charge a 1990 TR?
Use r12a. Drop it in without any change over. As far as your question goes you need to take the r12 weight and convert it to the r134 weight. You can google the conversion factor. The original r12 weight should be in the engine compartment or service manual. You will need to flush and change the oil as well as replace the drier and desiccant as they are not compatible with r134.
