I'm not much on electrical unless it 3 phase and then I just limp by. Since nobodys answered, I'll try to help. I'd say it could be, the fan itself, a relay, a fuse, a switch or possibly a broken wire. If you have a meter or a test light you can start at the fan plug and see if your getting power and work your way back from there. Which fan is it? A diagram will help you sort though things.