I can't see what you're working on, but what are you trying to save? The evaporator core? I'd be getting a new one if I was going that far anyway. Just cut the lines and get the nuts off on the bench if you have to. Bolt cutters, cutoff wheel, sawzall, or hacksaw can go through that line in no time.
If you need to save something, can you put some heat to it? I think a MAP gas torch would do, don't have to get it glowing just a little heat to expand the nut can help a lot. Also if you can get it hot enough to melt some wax into both ends of the nut that may help if heat alone doesn't do it. A piece of exhaust heat shield from any car can help deflect heat away from meltables/flammables. Another mechanic trick would be to have a friend very securely hold the crow foot with a long 1/2" ratchet through an adapter with the shortest extension possible. Then put the open-end wrench on the nut and hit in the loosen direction with a hammer. Can be used in conjunction with the heat. Works best if you have good fitting wrenches and strong friends.
I hesitate to ask, but I still do it every now and then myself. Are you going the right way? If the nut is on the line coming from the engine, it'll be 'backwards.' Just sayin...
Also, if you're doing a R134a retrofit, I would greatly enjoy a parts list after you've got everything working. It would save some work when I do mine.