A bit further down from the picture of R2D2 air-con draining machine it says this:
"Now, onto the aircon pipes. DO NOT do this if you still have aircon gas in the system. Undo the 2 10mm bolts holding in the aircon pipes, quite fiddly if you have abs, the charcoal can can just be moved via undoing its 2 10mm bolts. Once these are undone pop the pipes out of thier sockets, and move onto the 2 10mm bolts holding the surround plate in. Once out the way, go back into the cabin and give the heater box a wiggle. Bobs you're uncle, fannys your aunt, theres the little blighter!!! Undo the 4 x screws holding the long air vent in place on top of the heater box, then undo the clamps on the water pipes and the matrix will just pull out...."
To me all that has to be done to get the box out. Well that's my interpretation of it.