If you ever replaced a HDD in an iMac (pre-flat, and post white kinds), you've probably had a very loud fan and found iStat Menus or SSD Fan Control to fix the noise because you didn't want/need/know about getting a thermal detector. They are both awesome apps so check them out if you've just been living with the fan being on all the time or thinking about installing a SSD in your old iMac.
I recently got iStat Menus because I also needed to see the temps in my dying iMac and it comes with a fan control as well. I still had SSD Fan Control installed because I didn't know about the fan control till later. They now fight to control the HDD Fan but SSD Fan Control always win, leaving the fan running at different speed than what you set in iStat.
I finally bugged the developer over at Exirion for SSD Fan Control for uninstallation help.
I added the unloading of the service first, then remove the daemon and app.
sudo launchctl unload -F "/Library/LaunchDaemons/net.exirion.ssdfanctrl.plist" sudo rm "/Library/LaunchDaemons/net.exirion.ssdfanctrl.plist" sudo rm -Rf "/Library/StartupItems/SSDFanControl" sudo rm -Rf "/Applications/SSD Fan Control.app"