I was hoping that someone with more experience would reply. I troubleshoot aircraft electronics systems for a living, I'm not even familiar with my own Discovery yet, but I can understand wiring diagrams reasonably well. That is if they have enough detail and are correct.
Referring back the Haynes manual, the only reference material I have on hand, there are two relays which must operate to turn the fans on. I wouldn't be able to tell you where they are. Another possibility is that the fan switch, which turns the second of the two relays on, may have failed.
I doubt that I've been much help, hopefully someone else will be able to help.
Ron Thompson, VE8RT
Yellowknife, NT, Canada
"Who are are these that fly as a cloud, and as doves to their window?" Is 60:8