Chosen Solution
I have replaced my HDD with a Crucial M500 480gb SDD. Now when computer boots up CPU fan runs at full speed all the time. I have tried HDD fan control but still can’t get the fan to slow down. Tried it again with original HDD installed and fan was normal.
Sorry I missed seeing this question when it was posted. Apple used proprietary heat sensor hard drives on this model. Changing the hard drive will cause run away fan issues. To rectify this use the OWC thermal sensor listed here: https://eshop.macsales.com/item/OWC/DIDI…
Have you checked your serial number on this site: http://www.apple.com/uk/support/imac-har…
