How to control fan speed in macOS Sierra? After replacing the hard drive in my 2009 iMac 27", I noticed that the hard drive fan spins at maximum speed since the sensor cable is not plugged in. (The new SSD drive doesn't support it)

To solve this issue, I installed a software called "Macs Fan Control" that can read out the temperature from the SMART status of the drive and control the fan speed itself. 

This was a near-perfect solution until I upgrade my system to macOS Sierra. Now both "Macs Fan Control" and also "smcFanControl" can't control the fans anymore and the latter reports that I am running it on an unsupported system.

Now my question is, can I somehow control the fan speed manually using Terminal etc. or do I have to "trick" the sensor hardware-wise?
I am a firm believer in avoiding software "hacks" to fix hardware issues.  To fix this problem, you need the sensor.  Unfortunately, as you have found out, your SSD doesn't support this connection.

However, OWC makes an digital inline temperature sensor.  Basically, it goes between the SATA power cable and the SATA power connector of your HDD/SSD.  The temp sensor goes on your drive.

The best part about this is that it's a "once-and-done" solution meaning future OS upgrades won't be susceptible to software incompatibility problems like you are experiencing now.



C|Net did an article on this exact problem and a review of this solution.