Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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How do I access HDD fan for replacement?

HDD fan runs at full speed when it comes on. Speed does not respond to inputs from sensor other than to come on or go off. (It fails the 'fan test' run by TechTool) I have replacement, but need to know what to do once the glass and LCD are removed.

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Did you change the hard drive?


My thanks to all of you for your help. Obviously, the adapter with external sensor from OWC is the answer to not only my current issue, but my intended future upgrade to an SSD as well. (This iMac is a refurb I just purchased as my once trusty 2008 model died and is RIP in the garage at the moment.)


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I don't recommend using software to override software to control the systems fans as they tend to mask Vs fix the underlying problems. Besides many don't do it right so they burnout your system prematurely!

I suspect you replaced your hard drive with ether a new hard drive or a SSD. In either case you need to replace the now missing thermal sensor the system is expecting a signal from otherwise your system goes into fail safe mode running the fans at full throttle. Overtime the fan's will fail as they are not designed to run at this high RPM for very long and you will be thermal shocking your system which will lower its lifespan.

So here's what you need: OWC In-line Digital Thermal Sensor for iMac 2011 Hard Drive Upgrade.

If you didn't replace your drive then you'll need to dig a bit deeper here on whats happening. I would strongly recommend you get this app: TG Pro For less than $20 its well worth it! It will help you narrow down whats the root cause of your problems.

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Perhaps this is your problem, an I quote from ifixit's page for that device:

The iMac Intel 27" EMC 2429 Is largely unchanged from it's predecessor with the exception of some internal lay out and an inconvenient change to the hard drive; the internalizing of the thermal sensor. Moving the thermal sensor into the hard drive has done one major thing for this computer, it has made changing hard drive changes expensive and options limited. The thermal sensor wiring is now part of the SATA cable and is handled by proprietary firmware in the hard drive. In other words, even if you manage to attach an after market drive, you will be stuck with fans running at full blast unless you can find a fan controller.

Maybe if you found fan control software, that would fix it. I don't think replacement will help. If you do decide to replace it, use one of ifixit's guides for that Mac.

I hope this helps.

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@pccheese You are on the right track but let's see if they changed the hard drive and did not address the sensor. Then find the solution for that, (hint OWC).


Never mind Dan answered this while I was typing.


Sorry @mayer - Its dead here ;-{ I have nothing to fix. I'll likely go home early.


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pikur68 will be eternally grateful.
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