You will need to flush the entire system with an approved flush first especially if you have had a compressor failure, You also need to change the expansion tube (orfice) at the same time you retrofit.. You also need to add the compressor oil to the compressor itself while its off the vehicle thru the suction (low side) service port app. 4 oz.. And add app. 2 oz. to the new dryer.. Rotate the comp. pulley down to lubricate the front seal before installation.. Change all o-rings, Evacuate the system to remove all air and moisture once assembled, then charge.. There are several options on what to use but R12 and 134A are the only approved ones, all others may void compressor warranty.. I have been doing this 15 years for a living, and this is the correct way to do it.. You may cut some corners and not get the results your after.. I did my personal 85 vette 8 years ago, still blowing cold.. Tim