iMac 2009 CPU fans at high speed.

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Level 1

4 points

iMac 2009 CPU fans at high speed.

My CPU fans run very fast only a short time after startup. The computer is well ventilated etc but does get hot to the touch. Now running Yosemite, but the issue was there before. After 10-15 mins the fans are running quietly (1000-1400 rpm), but after 30 mins they have built up in speed to run at 4600+ rpm and very noisy with it, even with only safari open.

I've vacuumed any dust out from the vents at the base and the top slot.

I've tried the SMC reset. (Turn off, power cord out, press on button for ten secs, wait 5 secs, restart) but this didn't help.

Can anyone offer me another solution, please?

Here are the details of the computer

iMac, OS X Yosemite (10.10.1), 27" 12GB 3.06 GHz Intel Core 2 Duo

Posted on Nov 22, 2014 5:34 AM

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Answer 1

rkaufmann87

Level 10

148,914 points

Nov 22, 2014 5:38 AM in response to castor0700

Sometimes it takes 2-3 attempts for a SMC reset to work, please re-do it 2-3 times and post back results.

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Answer 2

Nov 22, 2014 6:03 AM in response to castor0700

Are you having any other issues other than excessive heat? you can install Temperature Gauge to assist where the issue is originates from. There is also an app called Macs Fan Control that gives you options either for system control, or based on ambient temp, or, even setting at a consistent rpm for any of the 3 fans on your iMac. This will also help to verify that all three are working properly. Has the iMac ever been worked on internally? if so, an improperly replaced cable will cause the fans to kick in. I forgot to mention if your CPU is overheating consistently, you may need to replace it.

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Answer 3

castor0700 Author

Level 1

4 points

Nov 22, 2014 6:20 AM in response to John Travitzky

Thanks John.

The only thing ever done was increasing the Ram from 4 to 12 GB - but this was only opening the slot at the base. Other than that the computer has never been opened. I assume that the fans come on and speed up because the system wants or needs them on to cool the computer (as I said - it does get hot to touch). If I instal 'Macs Fan Control' and slow the CPU fan could this damage the system?

Fingers Crossed, the computer otherwise works fine - but if you think there could be un underlying issue with the CPU - how could i diagnose it?

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Answer 4

Nov 22, 2014 6:47 AM in response to castor0700

The best way is to take it into an Apple Store and have them run a diagnostics. Really, this is the only way to test. Your CPU isn't running hot, so it may only be the sensor, or the fan itself that has the issue. Regarding the Macs fan control App... yes, if you override the system control, it could cause more harm than good. But since your system isn't really running hot, you can use the app to test a bit further. if you set macs fan control to Sensor based, it won't kick on unless the CPU heats up, therefore overriding the installed sensor on your iMac. This will tell you if the sensor is going bad, and also override it and keep your fan at a lower rpm. Hope this helps. I notice that your GPU is a bit hot, and this may be the cause for the fan coming on also.

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Answer 5

castor0700 Author

Level 1

4 points

Nov 22, 2014 11:35 AM in response to rkaufmann87

rkaufmann87 - I've reset it 4 or 5 times now. Still the same, back up to 4500+ after an hour or so, but thanks anyway. John - thanks again. I live quite a way from an apple store, but might be going in for an xmas shopping trip, i suppose I'll have to try it. Its all sounding rather complicated for me, CPUs and GPUs. I haven't reset the PRAM - whatever that is(?) - is that worth trying and how would i do it? Mike

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Answer 6

rkaufmann87

Level 10

148,914 points

Nov 22, 2014 2:05 PM in response to castor0700

OK the only thing to do next is test for a hardware issue, run Apple's Hardware Test in extended mode at least 2-3 times back to back. You need to do AHT 2-3 times back to back because it does not always pick up errors after the first or even second pass. However when it does find errors they are correct.

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