Does anyone know if there was any functional reason that there are 6 (3 on top, 3 on bottom) seemingly unnecessary holes in each side window de-mister duct? (I don’t know maybe to intentionally leak air out to dry out condensation inside the dash or something???)

I noticed this winter that my side windows don’t like to stay clear in the winter unless I hit defrost. I had my vents out as part of another project and I found open holes about the size of a very large grain of rice in each of the 6 places where the 2 halves of the duct snap together.

I sealed mine shut with clear-drying silicone and I am getting more air out the side de-misters now on def & def/floor settings. So for it seems like a promising mod but I won’t know for sure if it helps till winter.


3 holes in bottom of side de-mister duct

3 more holes in top of side de-mister duct

I caulked mine shut with clear-drying silicone

 

Aren't those holes for keeping the side mirrors defrosted? I've never torn a mirror off, but I know in the literature I have on my car it says I have them (side mirror defrosters).

EDIT = Nope, I was wrong:

The door mirrors have heating elements which work when the rear screen heater is switched ON. The mirror heater will clear all ice from the mirror surface.

 

Yep, side mirrors are electrically heated. These duct holes just seem to leak air inside the dash for no obvious reason.

 

The window directed side ports are pretty small, so the accumulated bypass leakage allowed by these clip recesses would likely add up to a tangible percentage of the total available airflow.
Could have been resolved either with better mold/clip design, or the addition of some felt/foam at the seam interface to better seal it and also the additional benefit of discouraging any possible expansion/contraction noises emanating from the join.

 

Those plastic parts gets complicated near the clips that hold everything together so compromises are made to reduce tool cost. Also the pressure in that vent is barely above ambient so leakage isn't much concern. Think about a compressor tank at 100 psi with a hole that size in it, air will be screaming out of there at very high velocity but a hole in a bucket full of air doesn't leak because the atmospheric pressure is the same inside and outside. That vent is closer to the bucket of air than a compressor, a small fraction of a psi of pressure. I'm just guessing it is a small increase in flow. Your mod certainly increases flow to where you want it so nice job. I will do the same mod you did if I ever have those vents out.

I am in agreement with Mark, a bit of foam in there would seal so better flow while also preventing noise. And I can see the cost engineer add to his spreadsheet 0.05 man hours x 100,000 cars/yr x 2 vents x 8 year production run x labor rate = nope.

 

And a third answer of the same kind from me:
Somebody, who designed that clip-on system during the X400 project, simply was not at his top-game. As a result, there is a bit of air leakage, which should not be there.
Also, there are tolerances in those moulded plastic parts. Using another design with seals would have been better, but the X400 project budget certainly would not have allowed for additional seals.
So, the only thing, which would have helped, would have been a better design (without extra seals).
Hence, yes, closing the unwanted air-gaps with any kind of silicon would be OK.