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My fan comes on when I turn on the computer and it never shuts off.

166 Views 2 Replies Latest reply: Nov 15, 2012 12:16 PM by rkaufmann87 RSS
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Nov 15, 2012 12:08 PM

When I turn on my desktop the fan comes on loudly and never shuts off. What can I do?

iMac (21.5-inch Mid 2011), OS X Mountain Lion (10.8.2)
  • John Galt Level 7 Level 7 (33,010 points)

    The first step is to perform an SMC reset. It is indicated for any anomaly associated with fans or power:



    Resetting the SMC for Mac Pro, Intel-based iMac, Intel-based Mac mini, or Intel-based Xserve

    1. Shut down the computer.
    2. Unplug the computer's power cord.
    3. Wait fifteen seconds.
    4. Attach the computer's power cord.
    5. Wait five seconds, then press the power button to turn on the computer.


    If you have not modified the Mac the fans should never be audible. I have tried and failed to make your model iMac's fans run audibly using Geekbench stress tests for hours on end. If it were not for Apple Hardware Test which exercises them, I would have suspected they were inoperative.


    If the SMC reset does not work then take it to Apple for evaluation. It has several temperature sensors with cables, one of which may have become detached.

  • rkaufmann87 Level 8 Level 8 (40,500 points)

    Reset the SMC, that should take care of it. To do so please:


    1. Shut down the computer. 
    2. Unplug the computer's power cord and all peripherals.
    3. Wait fifteen seconds. 
    4. Attach the computer's power cord. 
    5. Wait five seconds, then press the power button to turn on the computer.


    If it doesn't work the first time, try doing this 2-3 times.


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