Chosen Solution
I have iMac : Core i5 2.7, 21.5-Inch, Late 2013 I tried to upgrade HDD to SSDWhen I upgraded to SSD I started having fan problem: the fan started going at full speed. Since I don’t necessarily need SDD (and not sure how reliable are apps that control fan speed), I reverted back to originial HDD that came with iMacUnfortunately, even with original HDD back in its place, the fan problem is not going away. From what I have read, putting original HDD back should have solved the problem but apparently that is not working for me. Any ideas?
At this point I think you need to identify which sensor is either not plugged in or not working. I would recommend downloading this app: TG Pro it should show you what sensor is failing.
Here is the parts you’ll need: You’ll need a special inline thermal sensor adapter: OWC Complete HD/SSD Upgrade Kit Including Tools for all 27" iMacs 2012 & LaterAnd you’ll need a 2.5" to 3.5" adapter frame: OWC 2.5" to 3.5" Drive Adapter Bracket
shutdown your computer, unplug the plug, and then while the computer is unplugged, hit the power button. then plug it back it, and hit the power button to start it. then when the screen turns on, immediatly hold command alt p r until the computer screen goes black and you hear a chime. then release the keys and tada!
