Well considering he is an Essential character, killing him is impossible. If you have cubes in your inventory then you don't need to wait on him, otherwise make sure there is no enemies around and then try talking to him. He was a very slow annoyance to me when I did that quest, took him forever to actually get around to things. Another option is to try waiting. But all in all if your searching for the 5 cubes already then you should have a cube at least to open doors.

If he still doesnt do anything, and you have a cube put it into the receptical that lowers the water if you havent already, I found that triggers him into more dialogue... Otherwise keep trying to talk to him. If neither works than try reloading save before entering room? Mine glitched when I had 4 cubes.. put them into the boilers but the last one disappeared... So i had to take one from up top and transfer it into final boiler.

After re-reading your original post I just have to say this: There is no red cube. Its just the blue cubes are used for it all, they change color when you use them on the red door openers.