How to remove the discharge line for the AC

Are you talking about a spring lock coupler? There is a special tool for that. Your local auto store may have such tool? The only other fitting I saw, was a peanut fitting, pretty much self-explanatory.

I am not an hvac expert. I don't doubt your ability. When you open up the hvac system, when you put everything back, you need to pull a vacuum on system to make sure no leak. If you have a leak and add proper amount of refrigerant oil and refrigerant, your just spinning your wheels, it will just leak out.

If somebody else wants to post up with more hvac info, they are certainly welcome to the donation, no problem.