When I retrofitted my 760T A/C from R12 to R134, I put in all new Volvo parts from Swedish Engineering including new hoses. Soon, I found the entire hose from the compressor to condenser glowing green with UV dye because R135 was leaking right through the body of the hose. Later, I found out that Volvo has information out recommending use of barrier type hoses when retrofitting A/C to R134. It turns out, original hoses will hold R134 only when saturated with mineral oil used with R12. New hoses or flushed out old hoses (cleaned of mineral oil) will not hold R134 because its molecules are smaller than those of R12. I received and put in the car an original Volvo hose good only for R12. Be sure to put in new barrier type hoses designed to hold R134 when retrofiting from R12. Other recommendations from Volvo are to put in a more efficient condenser and condenser fan. I can attest these make a difference. I put in a VOV too. When I finished the job (and before the R134 leaked out) air out the vents was 36 degrees F in tropical heat and sun. Best regards.