Thanks for the replies.
The reason I ask is often arriving at the aircraft, the brake fans will be inoperative (1 brake fan inoperative) with a yellow sticker on the overhead panel, but the engineers will have the fans operating saying they have disconnected the fan that is not working. If it is written up then it should not be used as I understand, but if there were provisions for one fan to be inoperative then you could cool the other brake and still take off provided the brake with the inoperative fan was below your company limits.
This would save paying for an air conditioning machine to cool the brakes.