IMac slim fan runs constantly and processor is slow

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IMac slim fan runs constantly and processor is slow

SsdFanCtrl provided a temporary fix, Recovery mode was the cure!

Hardware: Apple iMac with the slim body, the Retina version.

One day I noticed the cooling fan running constantly (very noisy!) and running any application was hopelessly slow as if the processor was running at about 10% efficiency.

After lots of Googling, the favoured solution seemed to be to reset the SMC [System Management Controller] or to reset the PRAM. None of these made any difference, even after trying multiple times, just incase it didn't work first time.

I was pretty confident that this was not a Virus problem and started to worry that I might have caused some damage when I knocked it over a few weeks before. I did think I might have dislodged a heat sink which could possible have caused the problem. However, dismantling these version of iMac is impossible so I thought I was stuck with this problem.

I found a temporary solution for the fan noise by using a utility to slow the fan down, see end of article. However, the system was still running extremely slowly, almost unusable.

The solution - just re-boot to Recovery Mode!

As a last resort, I decided I would have a go at reverting the operating system to a previous version by using my Time Machine backup.

I Put the system into Recovery Mode in order to do this [Shutdown the system, then Cmd + R + Power on]. When the system came back on I realised the fan had stopped running at full speed. At this point I did not want to proceed with the recovery mode as it looked as though this action had cured the problem, so I forced a shut-down by holding the rear power switch for 5 seconds. I then powered on normally and the system works perfectly well and there is no more fan noise. Brilliant fix!

Purple tinted screen problem

Almost immediately following this issue, I had a problem with the iMac booting up with a pure white apple icon in the middle, which almost immediately turned purple-ish as the boot proceeded. Once the system was up and running the screen had lost its lovely brilliant white effect. However much tinkering with white-point on the Display utility, I could not get a pure white screen, it always had a purple hue.

The screen tint was cured by booting up in Safe Mode [Shut down, hold down shift and power on]. After Shutting down and rebooting in normal mode [just power on], the white screen returned to normal. I wonder if the mutitude of restarts, force quites etc had somehow created a confused config which Safe Mode managed to cure.

See also