Can Someone tell me what causes these spots on the headline

[General Snafu]

Can anyone tell me, what causes these two sets of double dots next to the A/C on both sides? I've seen them on several Chinooks. Mine came off with a carpet cleaning product called Tuff-Stuff but, I'm still curious what caused them?

[Concourse St Tropez]

I have them too....
It must be holes in the wood behind the carpet drawing in dusty air

[Blue~Go]

I had them, and also saw them on many Chinooks. Pretty sure I saw them on other brand RV's with ceiling Air Conditioners as well. I do not believe there are any holes (or any wood!) in these areas on our rigs. The central ceiling (at least in my generation and newer) is a fiberglass top, then 1-1/4" of nidacore (plastic honeycomb) type core, then a fiberglass inner liner that has hull liner type carpet glued to the inside (the part we see). There is some wood coring in the outer flat sections, but that's an inch or so in from the curve to the new level and is still covered by the inner fiberglass liner skin under the carpet. If you feel the ceiling it is hard. Drilling through even just the inner liner takes a bit of oomph.

My guess is that since the Air-conditioner takes in outside air and doesn't have much of a filter, that the spots are dirt that comes in from outside and is blown into the walls. As you may notice, there is often a larger dirt area just aft of the Air-Conditioner where I suppose the main flow blows out. I would guess there are some "gaps" that allow the same air to flow out the side in two mini-jets (with the same outside dirt) and that is what causes the spots.

[red_land_baron]

My guess is that at Trailwagons, they used some sort of lift to position the fiberglass shell over the chassis and these marks (like mine) are left from the rubber fingers that supported the shell during manufacture.

Comments?

RLB.

[Blue~Go]

Only reason I don't think so, is that I looked at a bunch of different types/brands of RV's before I bought my Chinook, and many of them had the exact same spots, in just the same place, to the side of the roof air-con. In fact, that's one reason I stopped worrying about them as some sort of potential defect in the roof or etc. of one particular coach/brand. I saw them on such a huge variety (Class A, Class C, fiberglass, aluminum, etc.), always in the same pattern, and they typically clean off just like dirt. Hence I still think they are dirt spots due to some "side gaps" in the roof air that allow dirty air to shoot out the side in a couple of spots (and there is typically a much larger dirty swath where the air is supposed to come out of the roof air).

On my Chinook, they cleaned off with carpet cleaner (as did, mostly, the larger one to the rear of the AC unit).