Any normal ac shop will charge the system because it has to be charged to check for leaks... then if they find any leaks the freon will have to be taken out, the item fixed, then recharged and checked to see that that was the only leak... doing just that with my 1981 wagon was going to cost about $175 keeping the very expensive R12. If your compressor is really good then the much lower cost of the 134a will help cover the cost of the 134 expansion valve,the 134 fittings, and the green seals that need to be replaced to change over...and it was suggested on the Tech forum that a parallel condensor would help the 134 more closely match the r12 cooling capacity... about $80 likely parts cost for that... Greg