You just bought the wrong version of this Noctua. The Noctua NF-A4x20 5v exist in 2 version 3 and 4 Pins and you bought the 3 pins versions (NOT PWM) 
Now will it work normally with just 3 pinsā¦ not sure if the fan speed should varyā¦
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For the 3 wire version only:
Bambu wire color ā Noctua wire color
Black ā Red (+5V)
Gray ā Black (GND)
Gray ā Yellow (RPM/Tach)
White ā not used
Your fan will probably just spin at 100% speed, which is fine.
The only thing that matters is that the Yellow wire reports to the controller board that the fan is spinning. I highly doubt the PWM is actually used or will ever be used.
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The board and everything else is the same as on the x1C which has a full enclosure (see my photos in the thread above). Yet the stock fan it uses is a 40x10 and (when it doesnāt break) it keeps everything cool enough. As long as you have some air moving over the heatsink itāll be fine. Iāve seen some people glue a tiny heatsink on the SOC (top left, see thermal photos above) but I donāt think anyone can prove if it makes the slightest difference.
So no need for an overkill fan IMO.
A standard PCB can tolerate up to 90C, thatās the board itself not just the ambient air. Some board go up to 110C or more. Even if the ambient air was 90C, your board wouldnāt reach that temp as long as thereās even a little breeze moving air around.
No need to goā¦ over-boardā¦ okay okay Iāll show myself out. 
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seems silly for Bambu to omit the main board fan from the P1P just to save like $2
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I did the Noctua swap as well, and remixed a bracket I found on Thingiverse to let a little more air through and to cool the whole MC board. Hereās what I did: Bambu X1 Carbon MC board Noctua fan housing by jwise0 - Thingiverse
I wish the firmware would drive the PWM lower when the MC board is idle. Itās still pretty noisy at idle. It would be nice to just leave the printer on so I could print when needed, and otherwise leave it thereā¦
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"Any old PLA will do. " - ouch, no it wonāt. PLA doesnāt age well in hot (enclosed) environments, even more so if you attach it straight onto the heat sink. Over time itāll become more brittle and itāll crack (at least print it in PETG). And if the printer is not enclosed, well then you didnāt need that fan as natural convection is sufficient (reason why the P1P doesnāt have one).
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This is a good point. That said, I sort of suspect that natural convection is enough in the X1C already, given that the heat sink is coaxial with the original fan (and, therefore, the fan is presumably not doing a whole lot to move air over the heat sinkā¦). Maybe one of these days I should stick a thermocouple on that heat sink and see how necessary it really is.
Iāve updated my Thingiverse description to suggest PETG. Thanks for the suggestion!
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Stepper motor drivers do get hot and do need heatsinks as a result, but they donāt need a ton of airflow or a big temp differential. Itās not a PC CPU weāre trying to cool. 
Buy any modern steppers such as TMC2209 and theyāll come equipped with their own individual tiny heatsinks. I would advise against running them without.
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I just had to reprint some parts I had previously done in PLA. They were holding up fine at 50C for about 10 hours before they warped, so now theyāre ASA
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I would love to replace the (to me) very noisy part cooling fan with something quieter. Sadly Noctua donāt make blower fans.
You would not want a Noctua fan for the part cooling fan as they donāt move enough air. Same for the hotend fan.
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But the cheapest Chinese fans do?
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The fans they are using do move enough air. Iāve been through replacing fans on many 3D printers and the only way you get adequate volume at lower noise is with a bigger fan.
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Sometimes less flow is also within the possibilities
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The two fans that matter are both radial fans, and Noctua doesnāt make radial fans, so you canāt replace them with Noctuas if you waned to. As for their size, I donāt see how youād get a bigger part cooling fan on the print head. Bambu Lab printers arenāt suitable for DIY the way say a Creality printer is, so Iām not sure what youāre getting at.
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If anybody fancies the solution (as did I) put forth by @SVDB, but would rather not cut/solder/splice wires - then the below bits will allow you to make a patch cable that converts from the Noctua PWM to the Control Board header.
The header is a JST MX 1.25 found here.
The Noctua PWM male connector is found here.
A SN-28B crimping tool will help the cause.
Here is a picture of the final cable:
This makes the replacement ridiculously simple along with the @SVDB bracket.
- Remove the back cover
- Unplug the stock fan
- Plugin the patch cable
- Install bracket with fan
- Re-install the back cover
Thanks again to @SVDB for the fantastic mod!
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Thanks for sourcing the parts! Exactly what I needed to clean up my soldering mess.
All the credit goes to @Nairod who came up with the idea for the placement of the fan. Iām just a copycat.
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Thanks for the help here. I was already on my second motherboard fan and it again was starting to sound wrong. I really did not feel like replacing the fan ever other monthā¦
I bit the bullet and just installed a 4020 like SVB
Printed the bracket in orange ABS so you can see how it sits nice and snug above the poop shute
Extremely easy install, especially if youāre used to combing through the cables from replacing the mb fan beforeā¦
The only hassle was getting the connectors just right. The fan connector on the board is really a tiny jst connector which I do not have in my modest electronics stock. I used a 2,5mm jst male connector and shortened it with a clipper and they miraculously fit the cable of one of the broken fans. Pushed those connectors in on of the connectors supplied with the 4020 fan and it works like a charm. Sorry Iāve got no pics, I was so excited it worked I taped everything shut to make sure everything was fixed in place.
I must say itās not that much more quiet than the stock fan. They sound about the same. (at least when the stock fan is behaving)
So for noise reduction, this is not the way. But why would you want the most silent fan on a machine to be even more silent anywayā¦
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Thanks for the wiring hints for the noctua, even i got my coupon from support to buy a new fan,
i just installed a noctua 5v, and hell its silent now
i dont want to replace that damn fan every 40 hrs runtime and im a long happy customer for noctua and im very sure the noctua will hold up much longer
i will use the coupon for some ABS fillament instead when availible
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Thanks for sharing, please report if you have any problems with the Noctua. I also think one replacement is already too many; making this a āconsumableā is a bad design choice, specially if the Noctua performs.
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