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  1. #1
    MacBook Air Loud Fan Under Zero Load
    The fan on my MacBook Air (Early 2015, Mojave), which typically doesn't turn on at all (or to an even slightly audible level) even during high CPU load, inexplicably turns on and stays on every few days. Checking activity monitor, the CPU is 95-99% IDLE and no processes are using more than 1-2% CPU, using iStats to check CPU temperature it's between 35-45 C which is low. Again, the fan doesn't usually turn on to audible levels even during moderate to high load, so I can't think of a reason it would come on with NO load. Interestingly, simply closing the lid and letting it sleep and opening it a few seconds later and the fan quiets down again! What's going on?

    I've tried SMC and NVRAM reset, as well as a complete re-install of MacOS. This started happening only with Mojave, and never happened with High Sierra, Sierra, or El Capitan.

  2. #2
    MacBook Air Loud Fan Under Zero Load
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Keller, Texas
    Posts
    56,799
    Your Mac's Specs
    2017 27" iMac, 10.5" iPad Pro, iPhone 6s+, iPhone 7+, Numerous iPods, Mojave
    Is your MacBook Air still covered by Apple Care? If it is, have it checked out by Apple. In the meantime, boot the machine to recovery and use Disk Utility to check out the SSD. Intermittent problems are hard to track down, so every thing you notice that seems out of place should be noted.

  3. #3
    Quote Originally Posted by chscag View Post
    Is your MacBook Air still covered by Apple Care? If it is, have it checked out by Apple. In the meantime, boot the machine to recovery and use Disk Utility to check out the SSD. Intermittent problems are hard to track down, so every thing you notice that seems out of place should be noted.
    No longer covered. What do you mean by "check out the SSD?"

  4. #4
    MacBook Air Loud Fan Under Zero Load
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Keller, Texas
    Posts
    56,799
    Your Mac's Specs
    2017 27" iMac, 10.5" iPad Pro, iPhone 6s+, iPhone 7+, Numerous iPods, Mojave
    Quote Originally Posted by badAdjective View Post
    No longer covered. What do you mean by "check out the SSD?"
    Just as I said above. Boot to Recovery (command + r), enter utilities, select Disk Utility, and run First Aid on your SSD.

  5. #5
    Quote Originally Posted by chscag View Post
    Just as I said above. Boot to Recovery (command + r), enter utilities, select Disk Utility, and run First Aid on your SSD.
    No problems found.

  6. #6
    MacBook Air Loud Fan Under Zero Load
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Keller, Texas
    Posts
    56,799
    Your Mac's Specs
    2017 27" iMac, 10.5" iPad Pro, iPhone 6s+, iPhone 7+, Numerous iPods, Mojave
    Okay, that's good. But sometimes, Disk Utility doesn't give us all the information about problems with hard drives and SSDs. Keep making backups just in case the SSD or something else fails. If the revving up of the Fan continues, you might want to make a genius bar appointment and have them check it out. Apple Store genius bar diagnostics are free but if the machine needs repair, that will charge you.

  7. #7
    MacBook Air Loud Fan Under Zero Load
    IWT's Avatar
    Member Since
    Jan 23, 2009
    Location
    Born in Scotland, Worked in Scotland then England, Now live in Wales
    Posts
    4,848
    Your Mac's Specs
    Late 2015 5K 27-inch Retina iMac, 4GHz i7, 32GB RAM, 1TB Flash Drive, macOS High Sierra 10.13.6
    +1. Can't emphasise enough the need for backups; Time Machine at the very least plus a cloned Backup such as Carbon Copy Cloner (CCC), or SuperDuper! (SD!) - each have free trials.

    The reason is that SSDs can fail without notice and, secondly, it is virtually impossible to recover data from a failed SSD.

    Ian
    Ian

  8. #8
    I already have backups, I'm not worried about data loss. Yes, I'm aware I can go to the Apple store, but for now I'm trying to resolve this with the help of the online community, especially because it's such a difficult problem to reproduce, the best I'm likely to get Apple is another recommendation to reset SMC or re-install MacOS, which I've already done, or to replace hardware without an actual diagnosis which will be expensive and pointless. I'm trying to find out what might be other causes of fan turning on other than actual heat/CPU load. What else could be going on?

  9. #9
    MacBook Air Loud Fan Under Zero Load
    MacInWin's Avatar
    Member Since
    Jan 01, 2009
    Location
    Winchester, VA
    Posts
    4,964
    Your Mac's Specs
    MBP 15" Mid 2015, iPhone XS, an iMac, plus ATVs, AWatch, MacMini
    Actually, the Apple store has more thorough test routines than are available to the public, so while you MAY get an answer here, it is much more likely that you will get an answer at the Apple store. And if you don't like the answer you get at the store, you don't have to take their advice.
    Jake

  10. #10
    Someone in the Apple Support Communities is stating that the SMC controls this on a schedule to blow dust out of the insides, but thus far has not provided any documentation or reference to back this up. Has anyone heard of this?

  11. #11
    MacBook Air Loud Fan Under Zero Load
    MacInWin's Avatar
    Member Since
    Jan 01, 2009
    Location
    Winchester, VA
    Posts
    4,964
    Your Mac's Specs
    MBP 15" Mid 2015, iPhone XS, an iMac, plus ATVs, AWatch, MacMini
    Never heard of it, and I doubt it's true. The fans don't "blow" anything, they pull air out of the Mac and fresh air comes in through vents in the case. Accelerating the fans won't move much dust. It should more like something in the thermal sensors is intermittently telling the fans to run harder. But the Apple store testing may disclose what that is.
    Jake

  12. #12
    Yes I understand that the Apple Store is an option but I'm also here in this forum to find out if anyone knows anything about this other than to tell me to go to the Apple Store, which feels a bit like going to a car repair forum and being told to take my car to the mechanic. I know I can do that, but there are also forums that help people diagnose problems, offer DIY fixes, etc. and that is their reason for being. Now I appreciate the advice, but is there anything you or others might offer other than "go to the mechanic?" Testing software, command line tools, system logs, etc. or anything else that may be helpful that I haven't already tried? Thanks.

  13. #13
    MacBook Air Loud Fan Under Zero Load
    ferrarr's Avatar
    Member Since
    May 21, 2012
    Location
    Pawtucket, RI, US
    Posts
    5,356
    Your Mac's Specs
    L2014 Mac mini macOS Mojave, iPhone 8+ iOS 12, 12.9" iPad Pro 1 iOS 12, Pencil 1
    Quote Originally Posted by badAdjective View Post
    Yes I understand that the Apple Store is an option but I'm also here in this forum to find out if anyone knows anything about this other than to tell me to go to the Apple Store, which feels a bit like going to a car repair forum and being told to take my car to the mechanic. I know I can do that, but there are also forums that help people diagnose problems, offer DIY fixes, etc. and that is their reason for being. Now I appreciate the advice, but is there anything you or others might offer other than "go to the mechanic?" Testing software, command line tools, system logs, etc. or anything else that may be helpful that I haven't already tried? Thanks.
    We're more user, than mechanic. You may be waiting a very long time to get such a specific reply.
    -- Bob --
    Please backup. Everything has a life cycle, unexpected and warning free. Nothing will last as long as you want it to.

  14. #14
    Quote Originally Posted by ferrarr View Post
    We're more user, than mechanic. You may be waiting a very long time to get such a specific reply.
    Sure, I understand, I wasn't expecting a magic wand :-) just thought other users, like you said, might have some ideas, tests to run, logs to look at, etc.

  15. #15
    MacBook Air Loud Fan Under Zero Load
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Keller, Texas
    Posts
    56,799
    Your Mac's Specs
    2017 27" iMac, 10.5" iPad Pro, iPhone 6s+, iPhone 7+, Numerous iPods, Mojave
    I understand your frustration. I was in the repair business for many years before retiring and intermittent problems are always the hardest to pin down. One more thing I would recommend.. run the extended Apple Hardware Test to see if it spots anything. Sorry that we can't be more specific in trying to pinpoint the problem.

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