4 Replies Latest reply: Aug 20, 2012 11:03 AM by Gwyneth Llewelyn
7TT Level 1 Level 1

The fan on my macbook (model identifier 5,1) is running like crazy and I'd like to do a hardware test however, inserting the MacBOok OS X installation Disk 1 wiath AHT Version 3A143 provides a "Hardware Test does not support this machine" message.


Any suggestions to:

A) what may cause the fan to run, and

B) How I can get a hardware test run.

MacBook, Mac OS X (10.6.8)
  • kostby Level 4 Level 4

    Welcome to Apple Support Communities.


    The Apple hardware test isn't working, apparently because you have inserted a system disc for another model MacBook. They are not universal. If you've lost or misplaced yours, you can call Apple and give them your MacBook's serial number to order the correct original disc set from for a small charge.


    There are several common cures for a fan that runs constantly at high speed:


    1) SMC (System Management Controller) reset:



    2) PRAM/NVRAM reset (though it is usually NOT the cause of a fan running constantly)



    3) An app or process that is 'stuck' can cause 100%+ CPU utilization of a dual-core processor. It may appear in Activity Monitor as Not 'Responding'


    Open Activity Monitor, and click the % CPU column so that results are sorted in descending order (triangle points down). That will help you quickly determine which app(s) are using the most CPU.

    Screen shot 2012-07-24 at 12.19.44 AM.png


    4) Streaming video, editing video or music, intense games, and even Time Machine backups causes high CPU utilization in older MacBooks (especially my MacBook 1,1 and 2,1 with the GMA950 video chipset), causing the fan to run.


    Message was edited by: kostby

  • 7TT Level 1 Level 1

    Thanks for both quick and detailed reply.


    I failed to mention that I had already looked into and tried step 1 and 2. Checking out the Actvity Monitor had also been completed. Despite not showing significant use of process, I uinstalled and disabled a couple of services.


    Your answer did however make me look for another set of CDs, thank you for that. I ran the Apple Hardware test and it came back saying that nothing was wrong.


    I'm a bit baffled at that. As soon as my computer is booted up the fan starts running. Right now, the Activity Monitor tells me CPU is between 75% and 85%  - IDLE - and the fan is going. I have to try the SMC again.


    Thanks again for your response.

  • kostby Level 4 Level 4

    It is normal for the fan to run at high speed (6000 rpm) at power-on and boot-up for my mid-2007 MacBook 2,1 for a few moments. Not sure about more recent models.


    Once booted and logged in, then it should 'throttle back' to about 2000 rpm unless you have lots of (40 or 50%) CPU utilization.


    Over the years, dust can build up inside the case and drastically reduce cooling efficiency as well. There was also a thread around these forums about the thermal paste connecting the CPU and the heatsinks drying out over time, reducing cooling efficiency even further, if you're adventurous and want to go on a cleaning expedition. A blast of compressed air at the vents might be enough to either convince you that A) further internal cleaning is needed, or B) that it doesn't seem to be a problem.


    I used my son's MacBook Pro mid-2009 for a few days before I realized it even HAD a fan. Newer Intel Core2Duo processor on a smaller die using fewer watts and a more efficient video chipset combine to produce far less heat to begin with, and the aluminum case dissipates heat far more effectively!


    If you recently installed (reinstalled, restored) OS X and you have hundreds of thousands of files, the automatic file indexing for Spotlight can take a while - hours at least, and maybe days. It can be disabled, but I let it run to completion, because I like the search capability. There are also OS X 'maintenance' processes that run automatically at like 3:00 a.m. if you leave your computer on overnight. If they don't run then, they'll try to run when you next start up, and that could be slowing things/causing more CPU utilization. Time Machine backups can also cause my fan to come on. If Time Machine is trying to do a backup almost immediately at start-up, that could also be the issue.


    I start the Activity Monitor app running in my system Dock at boot up, with the System Memory pie chart active. I've noticed that whenever the 'green' slice gets tiny (less than 100MB free RAM), the fan runs at higher speed, and beachballs are much more likely.


    My system is limited to 3GB usable system RAM. If you're still running with 2GB, an upgrade to 4GB is worthwhile. And if you're running out of free hard disk space (10 to 15GB FREE is a bare minimum needed for reliable performance), a larger 7200rpm hard drive (especially if your current drive is 5400 rpm) can speed things up.


    The current release of Safari 5.1.7 (6534.57.2) on Snow Leopard 10.6.8 seems to be a memory hog or has a serious memory leak over time. Safari can be the only app running, with only one tab open and can eventually cause free RAM to plummet. Flash-heavy pages seem to speed up the process.


    There are some Mac apps, free and paid that let you monitor and/or 'control' the fan. Monitoring it is fine, but I don't recommend trying to change the fan behavior. If the CPU is getting hot, it needs to be cooled!

  • Gwyneth Llewelyn Level 1 Level 1

    There is a further alternative, which sadly tends to get combined with the dust/thermal paste issue. As the Mac gets older, the original hard disk slowly comes to its end of life as well. When it starts to heat up — because of dust and any other similar causes — the hard disk gets its life even further shortened (that's one of the many reasons why data centers have air conditioning!).


    Another symptom for a potentially failing hard disk — well before Disk Utility and/or any SMART reporting tool finds anything wrong with it — are the annoying "hiccups": every now and then, the Mac "freezes" for a few seconds. There are never any errors on the log. What happens is that the OS is asking the disk for a bit of data which might be in a faulty area, and attempts it to retrieve repeatedly. This happens at a very low level so it doesn't propagate up to the logging system. The repeated attempts of retrieving data from the disk will heat it up and the fans will try to cool it down.


    This is often connected with an overall slowness of the Mac without apparent reason (i.e. no new software was installed recently). Since the hard disk is now doing an extra effort to retrieve partially damaged data, it takes a bit longer. As more and more bits of the disk start to fail, specially those related to kernel functions, the Mac becomes slower and slower. This is related from experience. It takes a lot of time until an error floats up to the surface: in one case, my old iMac's hard disk took a year until finally a few strange errors popped up on the logs (related to Spotlight and/or Time Machine) — other threads in the forums linked those to failing hard disks — and ultimately SMARTReporter and Onyx both showed that the disk was failing. Until that, all disk repairing utilities never found any problem with the disk. But after that, things happened very, very quickly until the disk terminally failed.