white dust coming out of AC vents - any ideas?

[willald]

We noticed since the end of our last trip (early June), that when air conditioning is running, the vents seem to be spewing out this white dust, constantly.

After we got home and parked it, came out to the RV a few days later, and underneath one vent, there is a pretty large pile of this white dust, that had all come out of that one vent. Air conditioner had not been running, but still a bunch came out of that one vent. Cleaned it up, came back and checked it again today, and now there is yet *another* pile of the white dust, under just that one vent.

Filters were cleaned just before last trip, and still look pretty clean. Its pretty obvious this is coming from somewhere in the ducting, probably close to that one vent.

Since this pile keeps forming even when AC isn't running, starting to think critter infestation of some kind, but there is no other evidence whatsoever of critters being inside. How could they get up inside the vents, anyway? I did 'punch' the ceiling several places where ducts are, thinking if there was a critter, you'd hear stirring. Nothing. Looked down ducts as best I could, again, no evidence of any critters.

Its as if the foam insulation in there has suddenly started working loose and coming out in tiny pieces. Rig is 9 years old, this is first time this has happened.

Has anyone else experienced this, or might know what it is and how best to fix?

[ocean_bound]

It is more likely the glue they use to glue the ceiling together is drying up and falling down they use a lot of glue and usually extra stuff that Spills out that’s not between anything will dry up in fall down I had the same thing happen to me mine was yellow tint to it and eventually just went away

[Rick_Jay]

Great! Now it if doesn't work, you can blame me! LOL

Hopefully that will be a permanent cure to the problem! 🙂

~Rick

[willald]

Update: Well, I took Rick’s advice, picked up some good quality foil tape at Lowe’s this morning, and set to work on the duct openings. Cut the tape in several strips about 1/2” wide, and used them to tape all around the vent openings so none of the 1” styrofoam insulation is exposed. Ended up doing this to every duct where we’d seen white dust coming from, a total of 5 of them.

Cranked up air conditioner, and….no more white dust. Problem solved. That foil tape is good stuff, seems to hold and stick really well. Will definitely keep it in the motorhome in case we need it again.

Thought about doing all the duct openings/vents, and may well on the future. All is good for now, though, so gonna move on to more fun stuff, like getting back out camping. 🙂

[Rick_Jay]

Well, without seeing just what your access to the areas is like, I think I'd be tempted to say try the foil tape for ducts. I've had good luck with that over the years. If properly applied it seems to stay in place for a long time. Whether it matters or not, though, I wouldn't buy it at a surplus store. I'd try to get a "name brand" or something with good reviews.

Good Luck,

~Rick

[willald]

Well, after taking the vent piece off and having a look inside the ducting, think I see what the problem is. Just gotta say this right off the bat: this is another example that shows just how shoddy this motorhome was built, haha. I am NOT impressed with how it’s built, has me seriously thinking about trading it for a quality built unit like a Newmar.

Anyway, the roof consists of a thin layer of some kind of plywood, then about 1” of solid styrofoam insulation. There is some kind of paper material glued down to the styrofoam insulation, then the duct cavity. Right there at the duct opening, that paper has come unglued from the styrofoam quite a bit, allowing air to get in between the paper and styrofoam where it ain’t supposed to get. Air blowing up into that styrofoam is blasting little bits of the styrofoam out. The duct opening we saw the most coming out, is where the paper has come up the most, but it looks like its happening at the other duct openings, too.

Sooo, how to fix this is the question now. Thinking about using some foil tape at each duct opening, and tape that paper back down all around it, to keep air from blowing up into the insulation. That, or maybe trying to glue that paper material back down around the duct opening with some kind of glue.

Thoughts?

[willald]

Rick Jay wrote:
Did you let Hunter Biden borrow it? LOL

Hahahah, I *KNEW* comments like this would come up. 🙂

[Rick_Jay]

Did you let Hunter Biden borrow it? LOL

~Rick

[dougrainer]

Your ducts may be filled with the dust. When I have had this, I use compressed air to blow out the ducts to remove any residual dust. Also, You HAVE to remove the Inside plenum to see and fix the gaps. Doug

[willald]

dougrainer wrote:
There is NOTHING in a RV rooftop AC unit that will produce debris or dust. What DOES produce this dust is, at EACH roof AC you need to make sure there is NO possible way the cavity of the roof between to top and the interior ceiling has open egress areas. If so, the AC unit will "pull" air and debris from this cavity as long as from the inside of the RV. The cavity will be behind the AC filter's, hence the fine debris. This is where AC Foil Tape comes in very handy to seal off those areas. If your AC units have the inside Plenum mount, you remove this mount and you will see the gaps on the 14 inch square roof cut out. SEAL those gaps and your problem goes away. IF top mounted AC you will have to remove the unit from the roof and do the same thing.

Thank you, Doug! I was hoping you'd see this thread, and might have seen this issue before and could offer some insight. 🙂

I will definitely check the cavity you mention here in the ceiling. I do recall some time ago, a mobile RV mechanic I had out doing some work on the RV, he put quite a bit of foil tape in there to try and make it more efficient.

Doug, if the AC unit is pulling this debris from that cavity....Why, would there be big piles of the dust under a vent, even days or weeks after AC unit has been off? That, is the part that really puzzles me, and has me concerned it might be critter activity of some kind. The 'piles' are only coming out of just one AC vent, also, the one over the sofa. Its one of the ones closest to the front AC unit. The rest of the vents only spew it out when AC is running.

[dougrainer]

DrewE wrote:
The part of the air conditioner on the roof is (or at least should be) separated from the ductwork side by a solid barrier, of course with some wires and tubes going through it. Outside air and inside air do not mix by design. If you think the source might be the air conditioner itself, it would be better to remove the inside cover/louver on the air conditioner unit and examine things from the inside. (There's no ducting as such on the outside side part of the air conditioner, just the shroud over the condenser, its fan, and the other external bits.)

Unless the powder is appearing from that air conditioner unit itself, I'd tend to suspect a source near where the pile is forming instead; but there's certainly no problem with taking a look at everything. If nothing else, it's well worth looking at the outside part of the air conditioner and cleaning out dirt or debris if needed to keep it working efficiently and effectively.

Bingo. There is NOTHING in a RV rooftop AC unit that will produce debris or dust. What DOES produce this dust is, at EACH roof AC you need to make sure there is NO possible way the cavity of the roof between to top and the interior ceiling has open egress areas. If so, the AC unit will "pull" air and debris from this cavity as long as from the inside of the RV. The cavity will be behind the AC filter's, hence the fine debris. This is where AC Foil Tape comes in very handy to seal off those areas. If your AC units have the inside Plenum mount, you remove this mount and you will see the gaps on the 14 inch square roof cut out. SEAL those gaps and your problem goes away. IF top mounted AC you will have to remove the unit from the roof and do the same thing. Doug

[DrewE]

The part of the air conditioner on the roof is (or at least should be) separated from the ductwork side by a solid barrier, of course with some wires and tubes going through it. Outside air and inside air do not mix by design. If you think the source might be the air conditioner itself, it would be better to remove the inside cover/louver on the air conditioner unit and examine things from the inside. (There's no ducting as such on the outside side part of the air conditioner, just the shroud over the condenser, its fan, and the other external bits.)

Unless the powder is appearing from that air conditioner unit itself, I'd tend to suspect a source near where the pile is forming instead; but there's certainly no problem with taking a look at everything. If nothing else, it's well worth looking at the outside part of the air conditioner and cleaning out dirt or debris if needed to keep it working efficiently and effectively.

[willald]

ItsyRV wrote:
One remote possibility that I doubt is the cause, but... Grab some of the dust and put it on white sheet of paper. Place another sheet over it and rub them together. Is the resulting smudge silverish? If so, your evap may be disintegrating. Have you recently cleaned the A/C or sprayed anything up into the return air duct? Your A/C is way too young for this to be a normal age issue, so if the aluminum is disintegrating, you need it checked quickly.

Interesting thought, but if that was the case, why is the white dust mostly piling up, when the air conditioner isn’t even running?

I do plan this weekend, to get up on the roof, take the cover off of the air conditioner and have a look around for any clues as to what’s going on. Want to make sure the ducting hasn’t somehow been compromised in there, to the point it’s allowed a critter of some kind to get in.

Will

[ItsyRV]

One remote possibility that I doubt is the cause, but... Grab some of the dust and put it on white sheet of paper. Place another sheet over it and rub them together. Is the resulting smudge silverish? If so, your evap may be disintegrating. Have you recently cleaned the A/C or sprayed anything up into the return air duct? Your A/C is way too young for this to be a normal age issue, so if the aluminum is disintegrating, you need it checked quickly.

[rexlion]

So that's where they hid the ricin! :E