I will let you know about the truth of imac's fan control.
If you have trouble with fan speed on you imac, than you should solve with software, not hardware.
first of all, you need smcFanControl application.
than try to fix it at terminal window.
Step 1 : Recogonize number of fan you have
/Application/smcFanControl.app/Contents/Resources/smc -f
Step 2: Change setting to force change (your stupid temp. manager can not change you fan speed anymore...)
/Application/smcFanControl.app/Contents/Resources/smc -k "fs! " -w ffff
Step 3 : Change maximum fan speed
/Application/smcFanControl.app/Contents/Resources/smc -k F#Tg -w 12c0
(put the numeric index of your fan at #, 12c0 = 1200 rpm)
** you should monitor the temperature of your imac with 1200 rpm. If it's too hot, you have to consider to change the rpm higher...
sorry for my poor english.
hope you get silence, too.
Thanks
Paul
ref : http://www.parhelia.ch/blog/statics/k3_keys.html
