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Christian Hofmann
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After changing HDD, CPU fan goes to 3500 rpm on power-on

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Hi,

I just removed my old HDD, just to install an SDD in the HDD slot, and an HDD (1TB SATA on SATA-to-IDE-cart) in my Optical Slot.

Everything seems to have gone smoothly, except... For seemingly no reason, my CPU fan goes to 3500 (CPU at 30-60°C), and my HDD fan to 1300 (HDD at 50°C). I think, at least the CPU fan shouldn't do so...

I already tried resetting the SMC, and reopened it to look if I maybe removed or forgot to reattach a temperature sensor, but both did not bring any solution at all.

Any Ideas?

Thank you!

Edited by: oldturkey03 ( ) , Christian Hofmann ( ) , machead3 ( )

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machead3
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Make sure you reconnect the heat sensor on the hdd - that could cause runaway fans. The other possibility is that those drives actually are overheating your machine. You could run a 3rd party fan app. to monitor internal temperature and see if it's really getting that warm in there.

If this Answer is helpful please remember to return and mark it Accepted.

Edited by: machead3 ( )

Actually, I forgot the first time. It really makes the HDD fan run errant. But I'm not sure about my CPU fan, this should behave normally, I suppose. Anyhow, currently all heat sensors are back in place, and CPU fan is still running full speed for no reason. In the meantime, I triple checked if I had any connection errors, or forgotten any fans - so, unless there's a magic dwarf in my iMac unplugging the temperature sensor every time I do not look, I still don't have any clue... Monitoring with iStat Pro btw.

Christian Hofmann,

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rob
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HDD Fan Control: http://www.hddfancontrol.com

It's designed specifically for this problem.

And, instead of the terrible answer above (which sticks the fans at 1500 regardless how warm the machine is), HDD Fan Control uses the SMART sensors to ramp up the fans when needed.

I really don't understand why this program is never mentioned when someone brings up the fan problem when you change a hard drive in an iMac... but there you go.

Rob - The correct answer here is to correct what failed, not band-aid it with something you shouldn't need. BTW Fan Control is not foolproof, as not all SMART drives have temp sensors and the spec is not clear on how it should be read. In fact, that is the problem with the late '11 & early '12 Apple iMac models which did away with the external sensor and Apple tried using an internal sensor that met it's specs. these '11 & '12 systems do indeed need Fan Control when you replace the HD with a non-conforming hard drive. Newer versions of Seagate & Western Digital hard drives appear to have conforming sensors now as we have had reports (and I've seen my self) of newer drives not needing Fan Control from the get go.

Dan,

One last point, Apple uses a few temp sensors in the system so it could be a different sensor was damaged in the process of servicing and/or a new problem has popped up. Without first diagnosing which sensor is going off and which fan/s are running and running correctly, your just shooting in the dark here. That is why you need to get a diagnostic tool like Temperature Gauge to read off the sensors and see what the fans are reporting as far as speed. Then you can figure out what the correct action is. And yes, I still often install Fan Control as a solution. But, I don't throw it on every system that has a thermo type of issue as the first answer.

Dan,

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Dan
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Go to the Mac App Store and download 'Temperature Gauge' App to monitor your devices.

Did you remount the thermal sensor onto your SSD from the old HD you took off.?

I remounted the HD sensor to the SSD and the Optical Drive sensor to the new HD. I'd rather had it vice versa, but the cables have just the right length to fit as intended by apple... So far, nothing I've done had any part heat over 50°C, so no cause for any fan to run at full speed.

Christian Hofmann,

Just to be clear here: You need to put the new HD on the original HD SATA connector and place the original HD sensor on it. The reason here is the first SATA interface temp sensor is calibrated for a hotter HD not a cooler SSD. If you reversed the expected devices you will need to splice the HD sensor cable with an extension to get it onto the HD or remount the HD back to the expected SATA connection. In older iMac's the optical drive I/O is PATA which I think swayed you into thinking you have to switch the devices around.

Dan,

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Chris Robinson
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Same thing here. All fans are now continually going crazy. Everything is connected fine. I don't get it. An SMC reset doesn't work. PRAM doesn't help. Makes no sense for all the fans to be going nuts. I wonder if it is related to the LCD temp sensor. I wonder if that could be making the fans ALL continually run.

Chris - Get the Temperature Gauge App and check that out. It's possible you have problem thats appears to be a CPU or HD problem.

Dan,

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Puru
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Download SSD FanController, open it and click on Manual. Put the numbers around 1500. That's it. The link is http://exirion.net/ssdfanctrl/. You may configure its preferences as to S.M.A.R.T. You'll find out when you download and install it.

If your issue is resolved, please come back and mark the answer as Accepted.

I'd rather not manually throttle my fans, but have the issue solved by the root...

Christian Hofmann,

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Christian Hofmann
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As I will have access to the AppleCare Help Desk Tools soon, I'll run a complete check and will keep you updated on this issue. Thanks for your suggestions up to now!

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Randall
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Anyone figure out what is causing the CPU fan to run a full speed?

Yes! the issue is the lack of a firm standard on how the thermo sensors inside the HD's are to be accessed. The SMART standard was not clear so when Apple decided to use the internal sensors in the newer drives (not all HD's have this sensor) they needed to custom fit a special cable harness to each vendors HD they were using. So when we go into these systems to replace the HD you either needed to replace the HD with the same vendors drive your given system has or you needed to replace the harness with the correct one for the drive you were installing. Also remember in some cases the HD being used didn't have a internal sensor which also created more of a mess. The good news here is the current crop of HD's all have an internal sensor now and many are now using the same pins and sensor.

Dan,

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