Rode my bike to work last week and sitting in traffic on the way home in 86degF (30degC) weather, the bike overheated but fan didn't switch on. Was able to get home OK. I thought maybe I had disturbed the fan power connection when I was in there removing the SAS. Connection was OK.
So then I applied 12V power from the battery to the fan - nothing (except a slight click...). When I removed the rad mounting bolts and angled it forward, I found some very fine gravel on top - like aquarium gravel (they are resurfacing the street we live on). When I span the blades by hand, some fine stones fell out. Then of course, the fan worked fine.
Just a heads up, the blades are easily jammed by fine gravel. So the click when I applied power was the fan blade trying to move but jammed by the gravel. A mudguard extender would help a lot because the front guard is so short at the back. I found gravel sitting on top of the rad itself. Then from there it just falls down the back and jams the fan. Pretty sure if I had known, I could have freed the blades by hand when I was out riding and the bike overheated (watch your fingers though... 😉).