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I recently used a can of compressed air to clear my laptop's air vents from dust and other dirt that accumulated over time. While doing so, I did not hold the CPU fan in place in order to stop it from spinning as a result of the inwards air flow.

Now, when the machine is powered on, I can clearly hear a rattling noise coming from the CPU fan. There is no noticeable increase in CPU temperature as far as I can tell. Besides the noise, it seems to work perfectly fine even under heavy load.

I'm interested in the technical explanation for what is happening and why it is happening. Also, is this a problem that can/should be fixed without getting a replacement fan?

EDIT

The noise is actually most noticeable when the machine is idling (i.e. when the fan is spinning at a moderate speed). As the fan speeds up under heavy CPU load, the rattling noise does not really increase in loudness, only in frequency and tone. I haven't had the chance to open it up yet, so all ideas are still welcome.

EDIT

I finally got around to taking a closer look, this is what I found: enter image description here

It looked pretty bad, but the problem still persists after thoroughly cleaning the fan. Any other ideas? I'm about to order a replacement fan.

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  • fans are calibrated at some point (you cant really calibrate plastic to 100%), the compressed air might have messed that up since you didn't prevent it from moving.
    – Lorenzo Von Matterhorn
    Apr 11, 2013 at 18:07
  • Did you blow into the vent, or did you open up the laptop?
    – Carl B
    Apr 11, 2013 at 18:08
  • @CarlB directly into the vent
    – Steven Liekens
    Apr 11, 2013 at 18:09
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    @StevenLiekens - you probably blew the dust/dirt into/onto the fan blades.
    – Carl B
    Apr 11, 2013 at 18:21
  • @StevenLiekens - Although the update is good about tone and frequency, you probably really want to address this soon rather than later. if something blocks the fan from spinning, it could get burnt out and / or heat will build and cause you other issues.
    – Carl B
    Apr 12, 2013 at 15:48

2 Answers 2

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If you didn't hold the blades, as you note, you may have overspooled the fan, causing it to spin much faster and deal with forces much stronger than it was designed for.

Blowing sustained blasts directly into a laptop vent is never a good idea. Short blasts obliquely are OK, but it's usually best to control the fan spin by holding the blade with some implement.

Now that the fan is probably damaged, besides checking for obvious stuff like Carl B suggests, you'll have to replace the fan.

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  • This turned out to be the case. The fan was broken beyond repair, so it had to be replaced. (Sorry for the delay. Other things got in the way.)
    – Steven Liekens
    Oct 6, 2013 at 9:25
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As you have blown into the vent, the one issue that comes to mind is that there is a blade or two with a little schmoots (dirt/dust) on it causing an imbalance. Now as the fan spins, the imbalance will give a rattling sound.

The other is that there is a clump of dust, hair or whatever around the fan shroud that the fan tips are hitting as they spin.

As you note the fan still spins and no temp problems are noticed even under load, it would seem that a loaded blade or two may be the problem.

You would want to open up the laptop to really see what is what and you will probably notice that the dust that was in the vent, in now spread around inside.

Some laptop fans have easy access to the blades and you can use a q-tip to wipe them down one by one. Not sure if yours is like this or if the shroud around the fan can be removed, but it would be a good first, cheap step to try. I would also, get some more air and when the laptop is open, give it another good blast.

DO NOT be tempted to use a vacuum cleaner. That could cause static/static discharge causing potential problems.

Laptop fan

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  • I'll try this as soon as I have the tools to open it up. I'd like to believe that it's not a problem with the fan's mechanical parts, but somehow I doubt it.
    – Steven Liekens
    Apr 11, 2013 at 19:02
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    I am optamistic that it is not ruined, but when you do open it and use air again, it would be wise to keep the fan from overspining, Just hold it and give it a good blast all around, turn it slightly, hold and blast again.
    – Carl B
    Apr 11, 2013 at 20:45

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