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Fan doesn't spin automatically on-boot with the 4924. It only turns on under heavy load; if you want to test it, run something load-heavy and wait a bit. It'll turn on.
If the unit isn't shutting down, or throttling performance due to the heat, and you have 5v on the fan, and the fan is plugged in, then it's probably fine. It's certainly POSSIBLE there's an issue with the fan, but I really think it's just not being told to turn on yet. Run FurMark on it for a few minutes at 4X AA. It'll turn on. If not, it will shut down. Either way you'll find out the issue. My money is on the fan being fine.
You would be surprised HOW hot these things can get before the fan turns on. Again, if the unit isn't shutting down or throttling performance, it's probably fine. I've had so many customers think their unit was broken because the fan didn't spin. After 5-10 minutes of FurMark/CPU stressing via terminal, the fan kicks on fine. Try it.