Fuse 18,20,and/or 21 under the hood should stop the blower motor from running(the blower motor at the right side of firewall).
If it's the blower motor under the armrest then it is fuse #1 in the trunk.
Don't leave the fuse out as it controls other things.
I don't believe there is a relay for either of these fans as it is managed thru the controller(those buttons on your dash panel).
Not a MB tech-I just looked it up!!