I believe you are exactly correct. If you simply put the die in, it will not circulate and thus not leak out. I just watched a video (thinking I was going to have to do this a couple days ago) and it said to add dye as well as freon to get the pressure high enough to kick on and circulate the dye .....

OK .... so I am no expert just a diy type of guy. I have replaced two compressors in the last 10 years. Both times I used a compressor from a discarded refrigerator as a vacuum pump. To everyones surprise it worked great. Unfortunately it finally died. So, my wife's Dodge Grand Caravan just develope...