He discovers that the heat Heat Sink cooling fan, as opposed to the part cooling fan, is doing more than is asked of it and the overflow of this fan is cooling your part to the point that your part cooling fan isn't really needed.
As you can see in this picture the front fan at this size is covering not just the heat sink but is also blowing on the heat block as well. You really dont want this as it cools your heat block, which is a bad thing, making it difficult to trust your temperature settings, along with forcing your printer to compensate unnecessarily for it.
It isn't difficult to see that the overflow of air from this will also be hitting the part being printed as well.
This is not a good thing and a bad design choice as it takes away any control from you, and makes adjusting settings very difficult.
In the following pictures you can see a Prusa mks 2.5 extruder housing with the components they use, and the layout they chose as well.
The smaller Heat sink fan (On the left) is only blowing onto the Heat sink and the overflow isn't providing the same amount of interference to the part as the Creality. (Some overflow would be expected though)
The much larger part cooling fan with its directed duct on the front (In this case a modified duct to surround the part a lot more)
I'm not sure if you can make it out in the next photo of the Prusa clone, but the heat block itself isn't really receiving any direct air from either fan.
The problem with the Creality setup....
Is that the excess air being blown over your part, makes it difficult to control each aspect of the printing process. If you can control all aspects of the process then you have options where you can adjust and fine tune your print process.
In the following example I used my experience of my old i3 in setting up some (Very old, and had to dry is for 2.5 hours at 65) petg, to print a new duct for my CR-10 in order to try and take back some control of this process.
As you saw in the previous pictures, I modified my old Prusa i3 clone thing, with their extruder setup and found that with this, I could cool petg a little on about 20% to help with stringing and it worked really well after testing some settings.
Unfortunately the CR-10 forced me to turn off the part cooling fan altogether, and despite doing this, the Heat Sink cooling fan, was blowing all over my print causing it to lift away from the bed causing it to warp up.
Controlling stringing would have been a bloody nightmare on a lot of other more complex and larger prints as well. So we need to find a solution to this.
This tiny little part was always going to be the small kid, picked on by the school bully, and sure enough, even with the part cooling fan turned off, the part warped.
The section that did warp was a victim of its own design and too many years of experience in the back on my mind, niggling at me telling me it probably would.
Apart from turning off your part cooling fan the thing you can do to help with this, is to re-orient the part that is most likely to warp, to be facing away from the front of the fan and bed (Not always possible though).
So rotate to avoid the aggravate :-)
This warping isn't excessive either, and could also be fixed with a heat gun and a flat surface. The point of all this though, is that I dont have the control I had before, and don't like this one little bit.
Once the new part cooling fan duct is attached to the printer (Printed in White Petg here) you can see where it lifts from the side. In this case and only good thing about this, it is better than it pointing down into the path of the printed part threatening to knock the print off the bed the moment you walk away.
The question is "What do I do, to fix this?"
1. Use a smaller fan similar to the Prusa and to model a modified mount that fits the existing steel housing for it.
2. Block off some of the airflow along the bottom of the fan so it doesn't blow onto the heat block ie some kapton tape, placed across the bottom 1/3 of the fan. ???3. Block off the two fans with partitions so each one is only blowing where we need it.
3. Redesign a brand new metal shroud to accommodate the smaller Heat Sink fan and redesign the old part cooling fan with a better duct and fan.
4. Nothing, leave it alone.
My procrastination skills are "5th Dan black belt" so don't hold your breath waiting for me to solve this in a short amount of time, but I would like to take some control back over the decisions I make about setting up a print rather than being dictated to by this crappy design.
I'm not really asking for suggestions, look upon this as talking to myself and putting the redesign idea out there for others to take up this challenge. I will come up with a decision and design sooner or later.
Will test the new duct later. Here is the link to the Thingiverse file I chose.