Fan running in sleep mode

[Bill Gates Jr.]

Lately, when putting computer in sleep mode vs shutdown mode, I can hear my fan running. Never noticed this before. I know my bad hearing has not improved, so what is causing the fan to run after going into sleep mode? Is this normal? Or it a sign that a fan hardware problem is becoming worse? Pete

 

[chscag]

Assuming it's your iMac that you're referring to.... No, it's not normal for the fan to remain on when the machine is sleeping.

Try resetting the SMC to see if that cures it. I had that same problem with my iMac when I was running High Sierra. After installing Mojave it never occurred again. I'm currently on Big Sur.

 

[Rod]

I agree with chscag on this really your fan should not run during sleep but maybe if the device is still hot when it goes to sleep it may run for a little while. Does it run all the time or does it stop after a time?
One of the interesting things I have noticed since upgrading my macOS to Big Sur is that it doesn't seem to get as hot as before.
I have iStat Menus running on my Menu Bar and I have an app which converts video formats, in this case MKV to AVI DivX. I have used this many times over the years for the same task and yesterday I noted that the processor core activity which used to max out during the process is about one third less on both cores and the temperature gain is not as great. It leads me to wonder if Big Sur is somehow more efficient at performing the same tasks with the same hardware than Mojave used to be.

 

[Bill Gates Jr.]

Unfortunately my iMac cannot run anything above High Sierra. Waiting to buy a new iMac once it gets the Apple chip.
Seems to be running all the time, although I haven't stuck around to check it after say 5 or 15 minutes.
I'll try resetting my SMC...once I figure what that is and how to do it. Thanks all

Pete

 

[chscag]

So easy, even you can do it.

How to reset the SMC on Mac desktop computers

1. Choose Apple menu > Shut Down and wait for your Mac to shut down.
2. Unplug the power cord.
3. Wait 15 seconds.
4. Plug the power cord back in.
5. Wait 5 seconds, then press the power button again to turn on your Mac.

 

[Bill Gates Jr.]

Tried it. No change. Just have to shut down every time I log off. Checked the fan temps and speed. Everything looks good.

 

[MarkAllread]

This might be a long shot but I had a similar issue with my Mac Pro.
Turns out I had just recently attached a cheap powered USB3 hub. Somehow the hub power bled back into the Mac when I put it to sleep and kept a fan running. I removed the power from the hub and everything returned t normal.
If you have something powered connected to your iMac, try disconnecting it.

 

[IWT]

@Ken, Good point. Whether it works or not, that's a useful tip.

Ian

 

[MarkAllread]

Thanks @ian, it was a weird one for sure. If I listened carefully, even when the Mac was powered off, it almost sounded like the hub was tying to start the computer up. Never seen anything like that before.