Ok, I posted a similar thread about this once but got no replies so I'm trying again. Basically I have 2 Cooler Master Megaflow 200mm blue fans. One of them works (plugged into the thermaltake mk1 fan controller) and runs all of the time which is what I want.
The other fan has been plugged into the mobo hasn't worked, used a 3 to 4 pin molex adapter hasn't worked.
This is what it does, lights up with its blue lights and that's it. Now if it has a thermal thing on it why isn't the other one not spinning. I've already replaced it as well. It is a side intake fan if anyone needs to know.
It was plugged in with its 3 pin to a 4 pin connection on my mobo lighted up no spin, I have another fan that came with the case thats plugged in like that and it works so there's no reason why it shouldn't work like that.
Right now its plugged in using the 3 to 4 pin molex adapter that the fan came with
It will be good if you can trouble shoot it first as suggested above by switching the two fans around. This will allow you to find out if the issue is coming from the fan or can be caused by something else.
If the fan is found to be defective, you can eRMA the product back to us to get it replaced. You will have to contact Cooler Master Support depending on your region.