iMac fan always on (recent development)

[ks-man]

I have an early 2009 iMac. I got it pretty soon after it was released (about a year ago). It was always very silent and had to put my ear to the back to hear the fan.

About a week ago the fan kicked on and now is always on regardless of what the computer is doing. I can have 8 apps open or none. If I shut down the computer, the fan turns off but kicks back on during startup.

The iStat stats says the Hard Drive is at 1600rpm and the CPU fan is at 1200rpm. I don't know what these numbers used to be when it was quiet. Those numbers don't look very high to me as my MBA exhaust is currently at 2500rpm and I can't hear anything from it. The iMac though is incredibly annoying.

Does anybody know what could be going on or do I need to take a trip to the Apple Store?

Thank you.

[Hellhammer]

Reset PRAM (http://support.apple.com/kb/HT1379) and do SMC reset (http://support.apple.com/kb/HT3964)

[spinnerlys]

1200rpm is the standard for the CPU.

I don't know about the 1600rpm for the HDD, my iMac (Alu 2007) has 1226rpm for the HDD fan.


MRoogle will give you many threads about this "issue".

[Hellhammer]

1200rpm is the standard for the CPU.

I don't know about the 1600rpm for the HDD, my iMac (Alu 2007) has 1226rpm for the HDD fan.


MRoogle will give you many threads about this "issue".

They are standards but I think iStat isn't giving the right measurements. My iMac is silent even when HD fan is running at +2000rpm. There shouldn't be almost any fan noise when fans are running at default speeds.

[ks-man]

Reset PRAM (http://support.apple.com/kb/HT1379) and do SMC reset (http://support.apple.com/kb/HT3964)

Thanks, I'll try that in a little while.

They are standards but I think iStat isn't giving the right measurements. My iMac is silent even when HD fan is running at +2000rpm. There shouldn't be almost any fan noise when fans are running at default speeds.

I agree that I think either the iStat numbers are bad or the fan just triggered always on regardless of the temps. I can hear the fan from 15-20 feet away and in the past I needed to place my ear to the back to hear it.

I'll report back after I reset the PRAM and SMC

[bobr1952]

I certainly agree that does not seem right. I use SMC Fan Control to ramp up the fans for certain things like WoW but at default, my HDD and CPU are 1200 range and dead silent. My WoW setting is 2500 for both and at that level, I can hear the fans from about the range you mention.

[ks-man]

I just reset both the PRAM and the SMC (first PRAM, then SMC) and the issue still hasn't seemed to be fixed. The fan shuts off when it shuts down, but as soon as it powers on and I hear the startup sound, the fan kicks on and never turns off. Any other recommendations?

Quick question, is there any way to confirm that I did the SMC properly? With the PRAM I can tell that the volume level changed, but with the SMC everything is powered off so I don't see anything different.

[Hellhammer]

I just reset both the PRAM and the SMC (first PRAM, then SMC) and the issue still hasn't seemed to be fixed. The fan shuts off when it shuts down, but as soon as it powers on and I hear the startup sound, the fan kicks on and never turns off. Any other recommendations?

Quick question, is there any way to confirm that I did the SMC properly? With the PRAM I can tell that the volume level changed, but with the SMC everything is powered off so I don't see anything different.

SMC reset is that you just unplug everything (including power cord) and letting it sit like that for a minute (some say that you should press the power button as well) and then plug in power cord and boot up.

After reading some threads about loud fan noise, I would just take it to Apple as several people have had defective heat sensors in aluminum iMacs.

[Pyrotechnic]

Mmmm. I have the same issue. Never heard the fan until recently, now its always there, although not fast, but noisy and annoying.

One think that really made my day when first switching was that they ran so quietly.

Im following this thread with great interest now.

I took out a 3 year warranty but live mies away from an Apply Store, so not looking forward to taking it, but needs must I guess.

[Richdave]

Any news on this?

I have a mid 2008 iMac and the fan is silent at boot and ramps up to a gale over a few minutes and stays there. I think the HDD temp sensor is the cause..