How To: CHEAPLY Replace Cisco Device Fans (Or Cisco LED Fan Mod)

If you’re like me and you like peace and quiet, saving money, and pretty lights, then this article is for you.

For financial reasons, I buy all the Cisco equipment for my home lab second-hand. The first thing to wear out is usually one of the cooling fans, so I often receive a unit with either dead fans or ones that have one blade in the grave. (Get it? Fan blade? …haha)

Replacement fans for Cisco routers and switches are usually priced around $50 by most resellers – I don’t even want to know what Cisco would sell them for. This becomes a huge problem if your device has 4 or 5 fans and you don’t have a large corporate budget backing you up.

What they don’t want you to know is that you can actually use any cooling fan to do the job. The only thing “special” about the ones branded for Cisco is that the pins are in a different configuration. Fortunately, with a little trial and error, this is something we can fix.

Now, before you consider replacing your fans, remember that the original ones do push a great deal of air for such small fans (most Cisco fans are 40 x 20 mm), but they have to or else the device would overheat under a full network load. Of course, this also means they are very loud. Consider this when you buy your fans – if you have a larger network putting your device under heavy use, you may need to spend $20 on each, but if your purpose is mainly a lab setup like me, a $5 fan will do nicely. Alternatively, if you’re looking at a device with dying fans and on a sharp budget, you may be forced to be cheap. I can’t find the specifications on how much CFM the original fans put out, but I recommend at least being physically familiar (as in, put your hand behind a working Cisco device) with how much air they are capable of moving… you need to realize how much you might be handicapping your device. The quieter the fan you choose, the less air it is putting out.


Finding the correct replacement fans from an online vendor is actually relatively simple, provided you follow these guidelines:

Size: 40mm x 40mm x 20mm
Connector: 3 pin
Voltage: 12v
Avoidances: Fans with external speed controllers or switches

You should verify the guidelines above on your unit… check that the connector is indeed 3 pins, see how many fans you have, etc. Unless you’re dying for all LED/silent fans, I recommend testing each fan one by one (unplug all except for one) to make sure you don’t have a good one that doesn’t need replacing. Also keep in mind if it isn’t under full load, you don’t actually need ALL the fans. If you have a device that comes with 5 fans and 3 of them are dead, unplug the dead ones and use the two good fans to move air from the power supply and the main processing chip – these are the two most important areas to keep cool. First, however, you’ve got to open up your device to get an idea of what’s going on. On my Catalyst 2950, there are only a handful of screws on the back and the cover slides off like most Cisco routers/switches.


Here’s what my Cisco Catalyst 2950 switch looks like with the cover off and the fan popped out of the metal clips that hold it in. The chassis actually has room for one more, but this board only provides power for a single fan, as you can see in Figure 2, as well as a close-up of the fan.


Personally, I love blue LEDs. Really, I dig anything that glows any color… so guess what kind of fans I chose?


Now, even though this fan’s connector looks the same (Figure 4: Cisco on the right) as the Cisco fan’s and fits perfectly on the motherboard, it won’t work offhand. Cisco wanted to discourage people from using other fans, so they changed the pin configuration.


Luckily, we can easily overcome this problem by popping the pins out of the connectors to rearrange them. You need something small and pointy – I used a thumbtack. Pull gently on each individual wire as you push down on the pin’s retention clip (through the plastic hole) with the thumbtack to release it. Don’t press down too hard or you will bend the piece of metal and your pin won’t stay back in the connector unless you have something even thinner to use to bend it back. Remember, these things are fragile and can easily break.


Once you pop all of the pins out, its time to start experimenting. Alternatively, you can see the combination that worked for me (Figure 7), but if for some reason that doesn’t work, keep trying. There’s less than 10 possible combinations, it won’t take long. I recommend not touching the pins directly to the motherboard without being inside their plastic counterpart because with things this small its rather easy to short things out. Remember, it won’t hurt your switch to turn it on without a working fan as long as your don’t leave it that way for more than a minute.


Halfway through, I found one combination that turned the fan on, but at a speed so low I couldn’t feel any air moving at all… it also made the LEDs blink very rapidly. Don’t get discouraged if this happens to you. Above, you can see my fan spinning full speed with the proper combination set. Lastly, here is the combination I used to make everything work.

Original: Pin 1 Pin 2 Pin 3
Blinking: Pin 2 Pin 3 Pin 1
Success: Pin 3 Pin 1 Pin 2

  7-completeflash400-thumb.jpg 8-completedark400-thumb-3.jpg

Alright. You’re done! Now you can sit back and be proud of the fact that you’re the only one on the block with a glowing switch. The fan I bought only puts out about 5 CFM, but they significantly reduce the noise level in my room from all my equipment.

Hope I saved you some money!  

taken from my blog

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