Hello!
I have just started a HEPA project on the housing fan.
Now I realize that my chamber fan is sucking into the printer and not blowing out as I thought.
I assumed that the air was being sucked out of the housing through the carbon filter, otherwise it wouldn’t make any sense. 
Is my fan installed/connected the wrong way round or is that the case? 
How is it with you, does it blow out or does it suck in?
The chamber fan should blow the air out and not suck it into the printer.
Are there any other users with a P1S who would like to check what their fan is doing?
The sticker on the fan should face outwards e.g looking from the back of the printer, you should be able to read it. The plug only goes in one way.
Just checked. Blowing out.
Thanks to everyone for the comments and for checking their printers.
@RMB
That’s weird, the fan sticker is facing outwards and the fan still sucks inwards!!!
Here is the clear proof:
But it’s nice that the nicotine fumes sucked in are neutralized by the active carbon filter and my components are not contaminated with nicotine!!! 
Perhaps those who have a poor flow to the outside should also check more closely whether the fan is actually blowing or sucking in!
As I said, it makes no sense at all. I don’t want to take the printer apart and check the air ducts to see if there is a deeper meaning behind it.
I’ll wait for your more detailed results and will probably raise a ticket with support if you have the same results.
I hope there is someone who can see the sticker on the fan and that it is actually blowing outwards.
You should be able to tell the flow direction by the direction the fan is spinning and the way the blades are angled. But anyway, I used the wiki when I installed my chamber fan to my P1P. Maybe your positive and negative worries are reversed.
Wait…it is sucking in, not pushing out! Huh I’ll be damned, i always thought what I’m feeling is the air getting blown at my my hand and not sucked away from it.
Now i feel dumb. What i assumed how it works was that the fan pulls the “dirty” air from inside the printer, through the carbon filter and then out of the printer.
The Chamber Temperature Regulator Fan is used to control the chamber temperature and to help filter the air inside the chassis. It can be manually controlled on the screen or the slicer.
@RMB
Perhaps the 3rd party fan that you have retrofitted has a different airflow direction.
In the P1S, the fan is permanently installed behind a rear panel (see video).
It also needs to be clarified whether it was deliberately designed this way or whether it is actually wrong.
But many thanks for your efforts with the instructions.
No worries, I purchased my fan from Bambu Lab, along with the P1S rear panel (so I didn’t have to drop holes in my P1P panel). I can check the airflow in mine for you tomorrow.
@xsynatic
No problem, I assumed from the beginning that it would blow out.
I was just surprised that my plaster didn’t come off the wall with the blast. 
On the other hand, I’m relieved to hear that someone else has had the same experience.
However, the direction of flow cannot be changed in the slicer, only the strength from 0-100%!
Yeah it should blow outwards, as it was originally designed to regulate the chamber heat (although the P1S doesn’t have a temperature sensor…). That is unless BBL decided to make it just circulate the heat around the chamber because it lacks the sensor, in which case it will blow air into the chamber.
@RMB
But then the question arises as to why Bambu Lab uses a carbon filter to filter the air that flows in from outside.
I had to go test this out again. I just printed and installed a hose mount over the fan to vent to the outside when I’m printing ASA, so I got a little paranoid that I was obstructing the flow if it is indeed pulling air in.
I did the flame test and saw that the flame was moving towards the machine, but then I noticed that it moves away and is even blown out when on the periphery of the fan vent. Did the same thing with tissue paper: the paper is pulled towards the fan and stays in place when in the center, but is blown away on the periphery. Pretty strong inward vortex but the overall net effect is air blowing out of the machine.
Even though the net effect appears to be outward flow, I’m just going to leave the hose off as the inward flow seems like it is not an insignificant amount.
It didn’t leave me in peace either and I brought the printer to my desk.
Once I had the front at the back, I took a closer look at the inside and outside without the top panel.
I also did the paper test on the outside. It held, but not in the same way as with PC fans, not very sucking, but it held. At the outer edge it swirled, strange air flow.
Now I opened the carbon compartment inside and took out the block and lo and behold, quite a lot of air came out the back.
Overall the airflow is pretty poor and caused all the fuss. Thank you for taking part.
Now that’s a thought; removing the carbon filter improved the airflow significantly? I’d be happy to remove the carbon filter in favor of venting to the outside via a hose. I’ll have to test that.
Addendum: Just tried it. Removing the carbon filter makes a huge difference in air flow. Makes sense, I just didn’t anticipate it being such a big difference. Keeping the filter door off also makes a big difference but I’m not sure if that’s too much and might cause cooling. I decided to keep the filter off, filter panel on, hooked back up the hose system to vent outside.
Yes, it does. Now I feel stupid that I didn’t think of it myself. 
In my defense, I have to say that I had opened the box once before and thought “aha, here’s the active carbon” and closed it again.
I did some tests regarding the chamber fan.
Not only does removing the carbon filter change it significantly, so does removing the rear cover. The holes are too small and are creating backpressure on the fan.
See this post (sorry it’s FB):
I’m just catching up on this thread, I’m not fan expert, but it seems like there is just too much static pressure “resistance” for the fan to actually move much air at all. (Just confirming that I see the problem too. It sucks in the middle, and blows around the edges.) (same as you all said) But, what’s the fix? I’ll probably remove the carbon box, as suggested, but kinda want it there. (Especially for ASA) So, I’m wondering if a different fan would help? maybe an adapted blower fan, that can redirect air outward through a small duct? (would probably be louder, which I’m not a “fan” of. 
) I might cut out the grill, as that might be the most simplistic approach. But I hate to hack up the asthetics. I’m also wondering, where is the largest restriction? Grill, or carbon box?
From my tests (see my videos on FaceBook, or I can try to upload them here also), it looks like the rear panel holes are the most restrictive.
Cutting it out would be easy, especially using a nibbling tool. I’d then print a fan guard (there are many online) or design your own. It could be held on with magnets, or screwed in as you choose.
If you didn’t like the results, a replacement rear panel is about $16, not too bad of a cost.
I’m hoping to get something soon to do a smoke test to see visually check the airflow. That rear panel is very restrictive.
My post mentions that it’s probably to help keep EMI emissions down to help it pass governmental standards and tests about EMI. I could be wrong, as I’m only guessing as to why those fan vent holes are so tiny.
