Chosen Solution
I have this same issue, late 2012 SSD upgrade with fan speed at 2,600 rpm’s all the time. I can’t find an answer for Late 2012, all the fan speed issues seem to be limited to 2011 and older. What gives? Late 2012 i7/16gb/1TB Fusion - upgraded to WD Blue blade M2 SATA SSD 1TB + 128gb Crucial 2.5” SSD. I just threw the 2.5” in as a PS scratch disk, but in the end I may remove it completely if I can’t control the fan speed (w/0 3rd party software) Here is my screenshot…
Update (12/07/2021) Sorry my post missed some info….no temp sensor…many said no fan issue on the 2012’s, maybe this was misinformation. Also, I used an adapter to fit the WD blue M2 2280 SSD 1TB. When I turn on the machine the fan speed is normal, within 1-2 minutes the fan speed increases to 2,600 RPM. Far as the SSD goes its working great. Here is what I used…
Did you use this iMac Intel 21.5" and 27" (Late 2012-Late 2015) SSD Temperature Sensor Its required when you replace the 3.5” HDD for a 2.5” SSD. This system won’t work correctly with an M.2 SSD alone. If you used an Apple SSD or OWC SSD they have the needed thermal connections.
You can also reset the SMC.
