iMac Intel 27" EMC 2309 (Late 2009, Core 2 Duo 3.06 or 3.33 GHz) ID iMac10,1, EMC 2374 (Late 2009, Core i5 2.66 GHz or Core i7 2.8 GHz) ID iMac11,1

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iMac 27" fan loud

Just replaced the hard drive and the fan sounds louder than before. Any ideas? I'm pretty sure I connected all the cables back up okay.

Answered! View the answer I have this problem too

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What model iMac is it? Earlier iMacs had a sensor on the outside of the HDD and it was moveable to a new drive, later iMacs have a temp sensor inside the HDD so you need to use the correct model specific HDD.

EDIT - i think all 27in models have sensor in HDD but happy to be corrected :)

THIS GUIDE doe not mention a sensor on the HDD

This ARTICLE may be worth a read too

UPDATE - Also if you are sure the HDD is correct type and cables etc are connected, try SMC and PRAM reset

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It's a late 2009 27" iMac. I didn't see any taped on sensor. I got a Seagate drive, the same as the broken one as mentioned in the guide.


The ARTICLE I linked has a Seagate 1TB ST31000524AS listed as compatible. Is that what you have? I didn't see a specific reference to a particular model HDD in the replacement guide or the teardown.. but maybe I missed it?


Rereading the guide - Step 10 of the GUIDE says Disconnect the thermal sensor, SATA power, and SATA data cables by pulling their connectors away from the sockets on the hard drive. When plugging the thermal sensor connector back into the hard drive, be sure it is inserted onto the set of pins closest to the SATA connectors and that the black wire of that connector is closest to the LCD Have you rechecked the sensor cable is in correct position as per the guide?


Thanks for your input. The cables are all back in the same position, and the the drive replace was a 'compatible' drive, but I still have this fan issue. The only thing that has worked is this plugin ($30) which adjusts the fan based on the readings from the SMART interface rather than the apple one. I don't quite get why Apple uses a extra heat sensor, if there's already a SMART sensor built in?


Mine is a 21.5" and I have the same problem EMC 2389 and its interesting that you say the two pins should be nearest the sata connector because it is the two pins furthest on the old drive and the connector is keyed. I could repin it if that is the answer.


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This problem is consistent with having not reconnected the thermal sensor properly. Check out 24 in iMac fan running constantly after replacing hard drive, particularly Majesty's answer. That should hopefully have all the information you need to correct your issue.

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