Why are the fans on my iMac constantly running at high speed?

Toastbeni November 8, 2014
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I changed my Seagate 1Tb HDD in my iMac late 2009 with a Samsung 840 Evo 120Gb SSD. I hot-wired the Temp Sensor, but now every time you turn it on the fans are running at high speed all the time.

I already had an SMC-based SSD Fan Control and HDD Fan Control on my Computer but it didn’t help. Then I put the old broken Seagate HDD in again (with temp sensor) but still the fans are running high. The only thing I noticed was that my frame is a little to high because now there is a small gap between the glass and the aluminium.

The iState showed that the temperature with hot-wire is 3 degrees Celsius without hot-wire its 9 degrees Celsius.

Please Help don’t know what to do :/
Thank you very much in advance for your answer :)

  1. Will Knot
    November 9, 2014 at 3:09 pm

    Just a question. Have you checked the Heatsink and fans to see if they are clogged with Dust?

  2. Jan F.
    November 8, 2014 at 5:57 pm

    Honestly, I haven't heard of either of these applications. smcFanControl is pretty much the go-to tool in such cases.

    I assume the late 2009 model already has the sensor that is connected directly to the hard drive? In that case the best way to go is to disconnect the cable entirely. Once that is done start the iMac back up and shut down again.
    Now, perform an SMC reset: unplug the power cable, wait 15 seconds, plug it back in, wait another 5 seconds, turn it back on. Within OS X check the fan speeds within smcFanControl.

    If the hard drive fan is spinning up to the max there is nothing you can do about it other than using smcFanControl to limit it's maximum RPM (within reason, 1.200 is a good value from my experience).
    If the CPU or optical drive fan is spinning up over 2.000 RPM then it's actually the LCD sensor that is not properly connected. It's one of the smaller cables you usually disconnect to take the LCD off.

    smcFanControl needs to be started to work - it does not run as some kernel extension or Launch Agent (last time I checked it, which wasn't too long ago).