After disassembly and reassembly to fix an HDD cable issue, my iMac is now a blowhard – the fans are going at full tilt from about 30 seconds after boot. I don't believe the device is overheating – I surely messed up one of the temperature sensors upon reassembly.
My question – beyond carefully checking each JST connection and making sure I've re-attached all the sensor cables on the motherboard, is there any way I can control the fans via software? I believe I have more-or-less permanently damaged the skin sensor – so can I disable that through software configuration or a 3rd party utility?
UPDATE
It's not the HDD / SDD temp sensor, by the way, since it's not the HDD fan that's spinning that hot, but it certainly is one of the other sensors. The ODD fan's RPMs are strangely high, but it's the CPU fan that's out of control. Mac's Fan Control is definitely doing the job for now (I'm using the CPU heatsink temp as my RPM controller). I'll need to get in there and determine which of the sensors is the one acting up.
I wonder whether I can tell which sensor is acting up based on either A) the list of sensors appearing in the Mac's Fan Control sensor list (or, more precisely, the sensor that's NOT appearing in that list) or B) the temperature of a given sensor that's way out of whack.
Best Answer
The thermal sensor is indeed responsible for this and the issue (if we can even call it one) has been around for a long time. Two or Three years ago, I upgraded my iMac from the original HDD to a speedy SSD and had to find out the hard way.
It quickly became apparent that the thermal sensor causes this to happen and I had to find a way to reduce the screaming 6300ish RPMs of the internal fan down to the usual 2000-3000 RPM range.
After searching the internet for software, I came across a lightweight application called SSD Fan Control that comfortably resides in my Applications folder and doesn't require my attention except for cases where the iMac clearly requires a little more airflow. However, because it is located in one location (contrary to a laptop), I am able to estimate its airflow requirements very easily.
Other options such as Mac's Fan Control have more customisation options but for me, lightweight was key. Furthermore, it was important to have it set up once and not be bothered by it. SSD Fan control has never given me a popup, ads or asked me to upgrade to a new version. I, therefore, strongly recommend it and swear by its easy to use and efficient design and practicality.