The whole procedure is covered in some details in TSM. I haven't checked manual for your year, but 89 TSM has a 4-page description with a lot of pictures (starts at page 72 of Heating/AC chapter). According to TSM, it doesn't require discharging the system, but it requires a sketchy step of drilling a hole through AC housing which might go very wrong
if you don't take precautions and drill goes too deep and penetrates the core.
I don't think there is any significant difference in regard to AC between 86 and 89 (I might be wrong), so hopefully that might help.
You can get a PDF of 89 TSM from Tom Collins site, here is a link
(it is a big
PDF, 300+ Mb)
Sometimes we reinvent the wheel not to have more wheels but to have more inventors
1988 Grand Wagoneer
- AMC 360 with ProFlo4 MPFI, TF727, NP229 FOR SALE
2021 JLU Willys EcoDiesel
- new shiny toy