Auxiliary fans running by themselves

Hi,

Thanks for providing this forum!

I just got a '96 C220 a couple months ago. Runs great, but tonight, the car was sitting in the driveway, and after several hours in below-50 temperature, the fans started running all by themselves.

I called the 800 number for Mercedes, and the tech that got on the line couldn't help, so I pulled the fuse for the fans.

I usually do most minor repairs myself, but I'm new to Mercedes. Is this something that's relatively simple, like a bad sensor or relay, or will this cost me a bundle at the dealership?

Thanks.