I've got a couple of scenarios I've run into when AC Quick disconnect lines not coming apart:
1. 2008 V6 Mustang:
I put a new accumulator on the AC system. The new aftermarket part I put on was faulty and would not come back off with anything I tried. I think the part was made just a little different than the OEM and would not allow to tool to expand the lock spring to release the pipe. I wrestled with this thing for hours! I ended up using a small sharp hook tool (and pair of scissors) to cut the inner spring. I had extras and they are cheap to place. These pipes should be able to move and twist and turn. These pipes did move so I knew they didn't have sealant on them.