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Model A1312 / Mid 2010 / 3.2 GHz Core i3 or 2.8 & 3.6 GHz Core i5 or 2.93 GHz Core i7, ID iMac11,3

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CPU fan on full spin after dual drive SSD installation

I installed an OWC SSD drive a secondary drive on my iMac 27" mid 2010 (2.93, i7, Mavericks 1.9.3) following the ifixit guide and the OWC video. On my model there was an extra unused SATA port on the logic board. I left the original Western Digital HD in place. When I put everything back together I forgot to push the RAM back in properly and got a black screen and one loud beep every 5 secs. I clicked the RAM firmly in restarted and then I heard the CPU fan spin it's little socks off.

iStat reported that the ODD and HDD fans were running at around 1000rpm. The CPU fan, contrary to the audible whirring, was reportedly spinning at 0rpm. Yet iStat is able to confirm the temperature for all the heat sensors, including the CPU's.

An Apple Hardware Test returned the 4MOT/1/40000002:CPU-0 error. Great, so I must have damaged the LCD temp. connector.

I removed the LCD and triple checked the LCD, HDD, Ambient, Skin temperature connectors. They all looked good. I didn't remount the LCD screen, but connected my external monitor and turned on the iMac – open heart surgery.

On start up both ODD and CPU fans run at full blast. As soon as the OS is loaded the ODD fan spins down to an acceptable 1000rpm. The CPU instead continues spinning at full throttle. I've tried resetting the SMC and PRAM a number of times.

With the mac open I started testing. I created a small shorting wire for the LCD temp connector and tested it, no difference. Shorted the HDD temp connector, nothing. I tried switching round the LCD temp connector pins, nothing.

While working on it I'd turn off the maddening CPU fan by physically disconnecting the CPU FAN connector which sits on the logic board to the right of the CPU fan.

I removed the extra SSD thinking that maybe the system needed an extra mysterious SATA 2 port heat sensor. But still the CPU fan ran like crazy. And I've also tried flipping the (4 pin, 2 cables) thermal sensor connector next to the PCB on the original HD so that the darker wire is facing out. Still nothing.

I then went the software route.

HDD Fan in demo mode only made the ODD fan spin faster - buggy and rubbish. Restarting was the only way to revert it.

SSD Fan Control was equally useless, obviously. It doesn't offer an option to override the CPU fan's settings.

smcFanControl seems to have no effect. I've tried creating custom fan spinning settings with it, but it doesn't alter any of the fans' spin speeds. I've also tried various flavours of the command /applications/smcfancontrol.app/Contents/resources/smc -k F2Mx -w 12c0. But still it doesn't override the CPU fan speed.

Lastly, I've only just noticed that the original HD SATA data cable was attached to the vertical port on the logic board, not the horizontal one as depicted in the installation guides. I may try inverting these.

What else can I try?

UPDATE: I've switched the two SATA data port cables (HDD vertical with SSD horizontal) on the logic board. Now the HDD is in the horizontal port and the SSD on the vertical one. It's made no difference.

UPDATE: I'm seriously considering hacking a resistor in place, as documented here.

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MACS Fan Control (link above) worked for me. I tried TG Pro, another fan control app and it didn't control anything.


I'd love any updates on this. I've done the exact same fix and am encountering a similar issue with my mid 2011 27" iMac. Please, anybody...


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It's most likely the hard drive temperature sensor cable. These machines had Apple priority sensors. They are Hard Drive manufacturer specific, using the wrong ones cause the fans to run at full speed. See this answer for more specifics: SSD compatibility (Thermal Sensor Connector))

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Do you really think this is the case even if I left the original HDD in place? All I did was add an extra SSD drive.


Does that sensor plug into your hard drive? Is it in the correct slot on the logic board? Did you read the info on the other question?


The original hard drive 4pin-2cable temp sensor is still plugged into the original HD that was shipped with iMac. I never touched it during while I added the SSD as a secondary drive. The HD's connector is also still plugged into its original housing port on the logic board. I'm pretty certain that is not the issue. As mentioned it's the CPU fan that's running wild, not the HDD fan.

And yes, I read that post you linked to. But it describes a different situation: where the original HDD is replaced byh an SSD, not one where an SSD is added. Or maybe I've misread it or missed something.


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SOLVED - Same symptoms after SSD + new HD into a 21" mid-2011 iMac. I tried all the same fan software, none of which worked.

BUT This one DOES work for me... CrystalIdea "Macs Fan Control"


Free, credible vendor (AFAIK). I have it set to sensor-based temp. control and auto-run on restart.

Now the fans spin up to crazy speeds on reboot and as soon as Macs Fan Control starts, they slow right down.

You can also use iStats Menus to put temperature display in the menu bar if you want to monitor the temps in your iMac.


Hope that helps


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Absolutely worked! Free download, 6 clicks and went from 3,900rpm to quiter than ever before. Thank you so much!


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@joshuatoro, in the end I added a resistor to the cpu's fan cables as documented in the last link of my original post. And here's the video to help you install the resistor.

Also, after 20years of macs, I've resolved never to buy another mac again. My next boxes will be a self-built linux and a hackintosh.

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Find and good, but they failed at the critical step and don't tell you what resistor was used!


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I have the same setup (and problem) - Macs Fan Control will solve the problem. At start-up screen fans go full speed, as soon as MFC opens the fans go down immediately. Set MCF as a Login Item so it starts up automatically when you log on.

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seb будет вечно благодарен.
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