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21.5' iMac fan speed is to fast

Hi all,

I've got a problem with my new 21.5' iMac. According to iStat the hard drive fan is spinning way to fast. Now this has been happening at least once every 8-9 days since I got this machine about 4 weeks ago. I've been searching this forum and the net to find a solution and there doesn't seem to be any. When I called Apple last week the CSR told me that when I'm not using the comp I should shut it down. I'm sorry but that's not the solution. Has anyone heard if Apple is going to fix this issue?

Wow! As I'm typing this the fan is now increasing in fan speed. Under iStat it's saying that it's the hard drive fan that's the issue. It went from 1099rpm and it's continuing to climb in speed. It's now over 4800rpm and still climbing. In the past I've never been at the comp when it's started doing it. I did take it to a local Apple authorized repair shop and form 2 days they ran some tests and couldn't get the comps fan to reproduce the issue. The tech said he called Apple and they are not even saying there is a problem. he seems to think that at some point Apple will send a firmware update down to fix the issue. Now I've had my comp back from the repair shop for 8 days now and low and behold I had the fan problem right on schedule. What should I do? Should I call Apple again?

Thanks so much,
Chevy

21.5' Imac, Mac OS X (10.6.2)

Posted on Mar 20, 2010 10:46 AM

Reply
527 replies

Mar 28, 2010 10:45 AM in response to chevy2410

Hey all,

Ok, I'm posting back with the results and I have to say it's not good. Early this morning, Sunday Mar. 28 2010, sometime between 1:30am and 2:45am, the fan in my iMac started spinning higher until it gets to the max, which seems to be about 5783rpm. I was in bed when this was happening and my wife had just gotten home from work and had heard the fan spinning way to fast. I followed resetting the SMC to the exact letter and it still did it. The iMac was working just fine for the whole week and like I stated in my first post it does this every 7-9 days and this time it was 8 days. According to iStat it's the hard drive fan that is the issue. So does that mean that the sensor is bad or perhaps the sensor cable? I guess I'll have to call Apple back and see what's going on.

Anyone have anything to add would great.

Cheers,
Chevy

Mar 28, 2010 11:25 AM in response to chevy2410

I doubt this will help but you can also try doing a PRAM reset. Here are the instructions. Please post back after doing this.

1. Turn off your iMac and unplug everything from it for 30 seconds.

2. Plug in the power cord, keyboard and mouse only.

3. Press the power button and immediately hold down the Option, Command, P & R keys until you hear the second gong then release the keys. Your machine will start up normally, then check for the issues you are having.

Roger

Apr 6, 2010 1:37 PM in response to rkaufmann87

Ok, reporting back. I tried to reset the SMC and the PRAM and no change. I've now been bumped up to senior tech adviser and we both seem to come to the same conclusion. That it must be a sensor that's not functioning properly. Now when I run iStat pro the fan in question is the hard drive fan. So apparently there is a sensor on the HD its' self and he's recommending to replace the drive. It's either the HD sensor or the sensor cable or it could be the sensor on the logic board. Either way this a first step and I hope replacing the drive will fix the issue. It's kinda funny that if it really is a bad sensor that it would cause the fan to spin up fast right a way and not every 8 days. I'm not kidding! Every 8 days on the button. The time of day is different, but it's every 8 days. Weird!!

Will keep you all posted.

Thanks,
Chevy

Apr 7, 2010 2:02 PM in response to Richdave

I never noticed what the temp of the HD was and actually I never knew there was temp for the HD. Now when this happened a couple of weeks ago my son shot some video of it and the temp of the HD then was only 36 degrees celsius. So it doesn't seem like it's really hot to cause the fan to spin up. Right now as I type the temp is 49 and all I'm doing is transferring some files from my imac to an external usb drive. The fan speed is the same as if the imac is sitting idle.

Cheers,
Chevy

Apr 7, 2010 4:25 PM in response to chevy2410

30C is a reasonable idle temp and 49C with light load is not a concern either. The fact that the fans are at a low and quiet speed at this temp is what you need to observe.

When next the fan is noisy, you need to check the temp. I suspect that the temp will be within normal range. This would suggest that the temperature sensor is not faulty but rather the fan controller as the fan should only increase speed as the temperature rises.

However if the temperature is reading abnormally high then either the sensor is faulty or the interrogating circuit is reporting a false high temp.

FWIW depending on your exact model, the sensor is either inside the HDD or clipped to the outside of the drive.

Apr 7, 2010 9:18 PM in response to chevy2410

The fan controller is most likely integrated into the logic board. From your first post it seems this unit is quite new so still under warranty.

If so then Apple should resolve it. I don't think that the described symptom, temperatures and fan behavior are indicative of a faulty HDD and/or sensor but I could be wrong.

I'd let Apple do whatever they think will resolve the issue and see what they come up with. Given it only happens every 8 days it does seem very strange indeed. Keep us posted on their work and outcomes..

Apr 9, 2010 7:50 AM in response to Richdave

Hello all,

I have the same problem with my 21.5 iMac. I had never really noticed the periodicity, but now that I think about it, it does seem to happen once a week or so. It just happened this morning when the HD fan speed was 6000+ while the temperature was in the 30s. Restarting the computer doesn't fix it. I have to shut it down and start it up again.

Please let me know what Apple says/does regarding your computer.

Cheers.

Apr 10, 2010 10:46 AM in response to Richdave

Yes my mac is still under warranty. I took it in to get it looked at via my local mac dealer and btw it's the second time I've had in the shop, and the tech there says he doesn't think it's the HDD or the sensor. He is really thinks it's a firmware issue and he says he's contacted Apple, but they aren't saying anything about the issue. He asked me to call him back in a few days and hopefully he'll have some more info as to what to do. I'm starting to see posts on this very issue more and more. What's the answer Apple?? Come on!

Chevy

Apr 14, 2010 7:52 PM in response to chevy2410

I have precisely the same issue with my 21.5" iMac.

Approximately one time per week the hard drive fan begins running at high speed. When this occurs, temperatures are normal and CPU load is low. Rebooting does not fix the problem, however shutdown and restart does.

When this occurs the hard drive fan runs up to 5000+ rpm and is very loud. This is in contrast to the normal situation where the fan runs about 1100rpm.

This issue has been occurring intermittently, about once per week since the machine was placed into service on October 24. The machine is stock - no internal components have been inserted/replaced since purchase. Most of the time, we are not actively using the computer when the problem starts.

I agree it is unlikely to be a sensor fault because temperature monitoring software shows the sensor is reporting normal-to-low HDD temps.

SMC reset does not fix this problem.

21.5' iMac fan speed is to fast

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