On Wednesday, February 5, 2014 11:47:31 PM UTC-5, wrote:
The fsu gets really hot at low speeds so the air flow its not enough to cool it down.At hi speed its cold .So that why i decide to add the fan .A cpu cooler will do just fine.

I did drill a hole were the transistor has that hole to be placed on a heatsink and added a screw so that the heat transfer is better in that area.

Saw your pics and sounds like you have a good design there that
should work. The idea of just making the fan go on when it gets
hot was a good one, so you could then just tie it to the 12V that
is already there. If you tied the fan to the 12V for the blower,
you might want to put an inline fuse in. That blower circuit is
30A? I've never seen a CPU fan like that cause a problem, but
just a thought. The fan may have some kind of protection of it's
own though, so manybe it's not an issue.

Good idea to screw the transistor down. I noticed that in the
photo, it wasn't clear exactly how they had it secured down.
And it's also near one edge of the heatsink, instead of being in
the middle. Before you modified it, was there thermal paste
between the back of the board and the heatsink?

This is just a really bad design. If they had correctly bonded
the heatsink directly to that transistor where all the heat is
being generated, I bet it would work fine.