CPU fan revving after SSD install ... Help!

Discussion in 'iMac' started by Jim L, May 15, 2013.

  1. Jim L macrumors regular

    Jul 16, 2011
    The Piedmont, NC
    Hi all.

    I have a mid-2011 21" iMac i5 (2.5 GHz) and did all my research before replacing my hard drive. I went with a 240 GB OWC Mercury SSD and watched all the videos from iFixit and OWC.

    My install seems to be in the minority of what other users did. I put mine in place of the original HD (as apposed to in place of the optical drive or in addition to the HD and optical drives) I did this because I really don't like spinning drives (noise, heat, slowness and eventual failure) and 240 is plenty of working space for me.

    Anyway, I got the drive in place (in an Icy Dock shell) and reattached the LCD cables and put the glass screen back on.

    Now on bootup there is a loud fan noise in my iMac. So loud I can't stand it. I did download SSDFanControl and it keeps the HD and optical drive fans at a nice low speed. But the noise was still there! I brought up another app called iStat Pro and it showed that my CPU fan is revving @ 3900 rpm.

    What causes this and what can I do about it? I read the very lengthy thread here about SSD installs and not many mention the CPU fan.

    Please help if you have a solution! Thank you. :)
  2. Macman45 macrumors G5


    Jul 29, 2011
    Somewhere Back In The Long Ago
    It's possible that one of the heat sensors either got damaged or disconnected when you installed the SSD....Only one way to check I'm afraid....Open it up again.
  3. Jim L thread starter macrumors regular

    Jul 16, 2011
    The Piedmont, NC
    Possibly the LCD temp sensor?

    Thanks. I'll give that a try and report back.

    One other remotely related post on the Apple Support forum seemed to suggest that the LCD sensor cable may not be seated correctly.

    Are there any hardware test tools that can tell what the fault is?
  4. toddzrx macrumors 6502a


    Nov 20, 2012
  5. Jim L thread starter macrumors regular

    Jul 16, 2011
    The Piedmont, NC

    Thanks so much man!
    I'm going to look at that also when I take the iMac apart again.

    I sure hope that I can fix this. If I can't I've already thought about what I'll do.
    (This computer is covered under 3-yr AppleCare and I've had it less than a year). I'll put the original drive in it and make Apple fix it.

    I really want a machine with SSD in it, but their new iMacs with that are way too expensive. I got this one for $999 as a refurb from Apple.
  6. tanker5 macrumors member

    Apr 19, 2011
    If I'm understanding you correctly, you simply swapped the original HD with the SSD. The mid 2011 iMacs (12.1, 12.2) have a unique temperature sensor on the hard drives. The fans are spinning at a high rate because the temperature sensor is telling the computer that it is not receiving any temperature data from the drive. This is why it was strongly recommended by tech blogs like ifixit and companies like OWC stated that the original HD disc in the 2011 iMacs not be replaced after the iMacs were first released.

    HOWEVER, a German company recently came up with a new type of temperature sensor that allows the 2011 iMacs to be able to accept HD discs and SSDs in place of the original HD disc.

    OWC offers a new kit with the new temperature sensor cable. I have one installed in my 2011 iMac and it works flawlessly. I have 2 SSDs in a RAID 0 configuration. And the speeds are blazingly fast.

    Installation is very tricky. It involves dismantling your entire iMac and removing the logic board in order to replace the temperature sensor cable. OWC has a step-by-step walkthrough video that shows you exactly how to do it. It took me a couple of hours to complete (partly because I was overly cautious when I did it).

    Here is the link for the kit:

    http://eshop.macsales.com/item/Other World Computing/DIYIM21HDD11/

    And the link to the video:


    Hope this helps. Good luck.
  7. Jim L thread starter macrumors regular

    Jul 16, 2011
    The Piedmont, NC

    Thanks to all who replied on this thread.

    The dreaded fan problem was due to the lack of temperature sensing from the drive.

    I ended up buying the following from OWC & Amazon:

    The install was a bit scary for me because I really didn't want to take the main logic board out. I followed the instructional videos from OWC and iFixit which were very helpful.

    Of course, now it runs lightening fast and there is no fan noise! :)

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