Sorry, I misunderstood which fan you were talking about.
As mentioned before the blower resistor might not work, also I saw this thread a while ago about the fan control. I don't know if this is the cause of your problem, but it might lead you in the right direction.
You can check out this thread. A couple of key posts by pizzaguy are #80 and 84. The part he talks about is very inexpensive.
Fan controller