I’ve upgraded my late 2009 iMac 27” with an SSD hard drive.

Because of the fan noise, I’ve installed SSD Fan Control, but I’m not sure how to set it properly, avoiding to reach high internal temperature that could damage hardware.

Using “SMART” mode fan are very quiet; using “Auto” mode are more noisy.

For now my settings are the following:

enter image description here

What does “1100 RPM @ 45 C” means? On the screenshot you can see that the temperature is 38°C, but the fan RPM is 1499...

Do you think these are good settings for me?

Thanks very much for the help


  • 1
    I'm voting to close this question as off-topic because it's a Basic Customer Support question. Please see the meta post linked above for details on how to proceed if you can edit the post and, if put on Hold, have the Hold reviewed. You can also contact the software developer for assistance with their product.
    – fsb
    Commented Sep 22, 2017 at 13:46
  • @fsb - Not so much a basic customer support question, but rather a dupe, an XY Problem and an opinionated question. I posted an answer to address the XY issue and a link to the dupe. The "opinion" part is now irrelevant.
    – Allan
    Commented Sep 22, 2017 at 14:34

2 Answers 2


The fan is running at 1499RPM at 38C, despite the settings of 1100RPM at 45C, because of a harmless bug in the SSD Fan Control app.

The bug is easy to reproduce:

  • Select Manual, and set the speed to 1500RPM
  • Select SMART, and the fan stays at 1499-1500 RPM

To "kick" the app back in to correct SMART operation:

  • Set the lower bound to a value below the ambient temperature (30C, for example), such that the fan speed increases
  • Set the lower bound back to 45C

Problem solved.

As for installing a temperature sensor, forget it. Francesco has a late 2009 model iMac 27" - these were not shipped with temperature sensors taped to the drive, rather with a proprietary cable connection direct to a special extra port on the drive.

The SSD Fan Control app works brilliantly on these old machines, once you understand the strange behaviour of this bug (and the workaround, described above).


This is one of those scenarios that leave me scratching my head because it's solution to a symptom without a basic understanding the of the problem (aka an XY Problem)

"1100 RPM and 45C" means:

  • The fan is spinning at 1,100 Revolutions Per Minute (RPM)

  • 45C is the temperature in Celsius (45 degrees Celsius or 113 in Fahrenheit)

Your fans spin up for one single reason only, the temp readings has indicated the the temperature is a certain level and needs to cool things down. What you have essentially done here with SMCFanControl is to override the system's ability to properly cool your iMac.

So, to properly control the fan in your iMac, you need to address the problem:

The issue, most likely, is that after your upgrade of the SSD, you didn't account for the in-line temperature sensor which sends the correct data back to the fan controller.

  • Hi Allan, please let me try to understand, because i'm not a technician. For you the only way is to install a new sensor like this one? eshop.macsales.com/item/OWC/DIDIMACHDD09 What i can't understand is why there are several software (like ssd fan control, macs fan control, hdd fan control, ...) that promise to solve the problem of who upgrades old mac with ssd like me. Thanks Commented Sep 22, 2017 at 19:10
  • The correct way is to install the sensor that addresses the issue. Just because there's software to do something, doesn't make it the right thing to do. To put it another way, can you stop someone coughing by giving them cough medicine? Yes, but that doesn't solve the problem of them inhaling the smoke that's causing the coughing.
    – Allan
    Commented Sep 22, 2017 at 19:14
  • Don't know about "SSD Fan Control", but:From the FAQ: "When I run smcFanControl and set a new minimum speed, will my fan speed still increase if the CPU load gets higher? Yes, fan speed will increase as defined by Apple. smcFanControl lets the fans stay in automatic mode and just sets the minimum fan speed. However, the higher you set the minimum fan speed, the longer it will take for the fan speed to increase." –– There are fan controllers out there that let you undercut these settings for minRPM. smcFanControl does not. Commented Sep 24, 2017 at 15:14

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