iMac Noisy Fan

The HDD of my iMac (24-inch, Mid 2007) crashed and I had to get a new one. After I changed the HDD, the fan started to run at full speed. The noisy fan was very irritating. I am running Mac OS X Yosemite 10.10.5 (14F27).

Figuring Out The Fan Speed

I tried the in-built spin dump to check at what speed the fan was running.

$ sudo  spindump
Sampling all processes for 10 seconds with 10 milliseconds of run time between samples
Sampling completed, processing symbols...
Spindump analysis written to file /tmp/spindump.txt

$ cat /tmp/spindump.txt | grep "Fan speed"
Fan speed:       698 rpm

This seemed too low to cause a noisy flag. Maybe it was some other fan. I googled around for more tools and came across smcFanControl.

Compiling Needed Tools

However, I could not compile smcFanControl. I had to install Make. Once installed, I got following error:

$ pwd

$ make
 gcc -mmacosx-version-min=10.4 -Wall -g -framework IOKit -o smc smc.o
 ld: warning: object file (smc.o) was built for newer OSX version (10.10) than being linked (10.4)
 Undefined symbols for architecture x86_64:
 "_main", referenced from:
 __start in crt1.o
 ld: symbol(s) not found for architecture x86_64
 clang: error: linker command failed with exit code 1 (use -v to see invocation)
 make: *** [smc] Error 1

Can’t XCode

Since I am running Mac OS X Yosemite instead of Mac OS X El Capitan, I could not get the latest Xcode. I thought of upgrading to El Capitan, but reviews on App Store pointed out that Xcode + El Capitan on 4 GB RAM is a disaster.

More Search

Finally after googling on Yahoo (I know!) using keywords ‘imac noisy fan’, I came across Macs Fan Control. They had a free and usable version of the software.

It showed me that there we 3 fans on my system:

3 Fans on iMac

This was first useful information. I tried setting limits on fan speed of each and soon realised it was the CPU fan that was the noisy one. The default sensor was pointing to the HDD. My guess is there is no heat sensor in the HDD I installed. So I chose another sensor.

Sensors on iMac


And finally … fan was silent!

Thanks to folks at Crystal Idea (@crystalidea).

Dinker has over a decade of experience in building products across diverse domains as Industrial Automation, Home Automations, Operating Systems, High Energy Particle Physics, Embedded Systems, Online Video Advertising, Messaging and K-12. He also founded Gungroo Software.
  • Patricia

    Thank you Dinker, I had the same problem with my 2010 iMac’s HDD and after replacing it I was alarmed at the fan noise. I tried Crystal Idea’s solution and it seems to have solved the problem. However I don’t have your expertise in adjusting the sensors so I hope that the silent fan means that things are truly functioning correctly.

    • jacobthejones

      This doesn’t solve the problem. All he did was tie the fan speed to an unrelated sensor. This means that the fan won’t kick on when the CPU starts to heat up. Instead, you should connect it to the CPU proximity sensor. The power supply proximity sensor is close to the CPU, but not close enough to safely use the sensor to control the CPU fan speed.

      • Patricia

        Thanks Jacob, I’ll check that!

        • ddiinnxx

          Hey, glad to know my write-up helped even if it didn’t have best solution. Now we both have a good one 😉

          • Patricia

            Yes, your posting and Jacob’s reply was a good find. My Mac is purring at a comfortable 34C 951 rpm…

      • ddiinnxx

        Yes, it was a hack. Tying to CPU proximity sensor sounds better. Will give that a try too.