Can you fit a fit a Lepa AquaChanger 240mm AIO Liquid Cooler in a Cooler Master HAF RC-912? Yes, but the fans will need to be mounted outside.
If you have a HAF 912 pc case and bought a Lepa AquaChanger 240mm AIO (All-in-One) water cooler with a 240mm radiator and they don’t fit, there is a way. You can fit them together but the radiator fans will not fit inside the case. The HAF 912 manual recommends you to put 240mm radiators outside the case, on the top of it and route the tubes in the back. There are two holes there designed for this. Unfortunately, this is not an option for the Lepa AquaChanger 240mm because it’s a AIO (which means you can’t remove any joint) and it’s tubes are too short for any customization.
The easier course of action is to put the 240mm radiator inside, facing the top, with the two fans outside of the case, in the top, pulling air from the radiator. You have to use the same screws to both hold the fans and the radiator, I had to try a few times until get it right. I also had to route the power supply to inside, for one of the fans I removed the top plastic cap of the case to pass the wires through there. I could keep the rear fan (pulling air from the case) in the same place, but using only one of the four screws as the other as misaligned now.
The disadvantage of this setup is that the fans are exposed and someone can accidentally break them by touching or dropping something on them. I added two 120mm grills later to mitigate this. Also, the fans are not in direct contact with the radiators so it’s not the most efficient setup.
Another option would be drill a hole on the top of the case, get fans and radiator outside, and route the tubes using the hole. It could work but it would require a hole big enough to pass the pump through it.
Update: I was building another pc and ended up moving this water cooler to a different case which supports a 240mm radiator nicely (DIYPC Gamestorm-BK).