Duct Condensation 3807 Salon Unit

[Bubbastump13]

We've got an '88 model 3807 that we totally love, but the AC ducting off of the Salon unit continuously sweats to the point that dripping water seeps back underneath the aft cabin walls and wets the carpet. I've been able to get insulation around all the ductwork for the aft cabin unit and the v-berth unit, but the way that the duct is chased inside the wall pocket separating the salon from the aft cabin vanity desk is driving me crazy! The flex duct appears to be squeezed into a flattened oval shape just off the unit inside the aft cabin closet where it has to go through a ridiculously narrow, oblong cut into the starboard side riser or stair framing(?) before apparently then connecting to a flattened box that sneaks up inside the wall pocket to the vent on the aft salon wall near the ceiling.

Does anyone know a way to access this duct without having rip through at least three different sandwiched layers of wall plywood? Going through the finished salon wall would be disastrous, as I'd never be able to keep from scaring and damaging it. I first tried removing the vanity desk framing, then pulled off the mirroring to access its plywood behind, but then removing that sheet only found MORE plywood?!

Help please?

[Viper]

Interesting, I don't have that problem but you likely have different conditions down there. I haven't had to get in there yet so I can't be of much help here. You're on the right track though, insulating the duct should solve the problem. Let us know if you come up with a solution or find access to that space.

[pepmyster]

Reminds me of the fan on top of your stove. During winter, if the duct work going from the stove fan, then trough the attic, then to outside, if the duct work is not isolated during the winter season , it will sweat. ( Don't ask me how I know). You guys nailed it. The temp difference is just reversed in your situation. Great answer Viper!

[Bubbastump13]

UPDATE: So, on a whim I removed the salon AC control panel and its mounting plate and that opens up about a 3x5 hole in the salon aft wall. Look what I found inside! Now, I just have to find a human Stretch Armstrong that can fit an arm inside and help me disconnect (yeah, right~!). Most importantly, a camera scan inside determines there's absolutely NO ACCESS unless I remove the external salon wall... Actually, I got to wondering if I filled this wall pocket with non-flammable foam, would that stop the condensation??? Hmmm!

[tomschauer]

Before you go to far check the simple things. Condensation will develop on the duct in certain conditions. (look up a copy of a psychometric chart).
If your air filter or evaporator coils are partially clogged, or your fan is running to slow, the a/c discharge temperature temperature could be cold enough to cause the condensation on the ducts. Normally, uninsulated ducts in a conditioned space will not condense.

Check these items, make sure your fan is running at the highest speed (higher air temp) until the humidity comes under control.

Another thing to look for, is if someone replaced the a/c unit with a larger capacity unit without upgrading the duct work to meet the required airflow of the new unit. This would also cause the discharge air flow to be reduced to less than required by the unit, lowering discharge air temps into the condensing range.

[Viper]

I'd have to check but have you taken a look at what it would take to remove the mirror over the makeup table in the aft cabin? I think this would give you access to that area. You'd likely have to cut the wood panel behind it unless there is a removable one but it would get covered back up with the mirror anyway.

[bud37]

Source of the post Actually, I got to wondering if I filled this wall pocket with non-flammable foam, would that stop the condensation??? Hmmm!

In my opinion filling that area with foam would not be ideal....there needs to be air flow thru all these areas, perhaps some vents cut into panels may help to get some much needed passive air circulation, the vents don't need to be huge and there are many sizes and shapes of decorative vent covers out there.....try and leave the area open for a while and see what happens if there is some air movement.

[Bubbastump13]

Source of the post Before you go to far check the simple things. Condensation will develop on the duct in certain conditions. (look up a copy of a psychometric chart).
If your air filter or evaporator coils are partially clogged, or your fan is running to slow, the a/c discharge temperature temperature could be cold enough to cause the condensation on the ducts. Normally, uninsulated ducts in a conditioned space will not condense.

Check these items, make sure your fan is running at the highest speed (higher air temp) until the humidity comes under control.

Another thing to look for, is if someone replaced the a/c unit with a larger capacity unit without upgrading the duct work to meet the required airflow of the new unit. This would also cause the discharge air flow to be reduced to less than required by the unit, lowering discharge air temps into the condensing range.

Everything said is true , but I believe its even simpler than that...the installed duct appears compressed and deformed significantly from its original installation in the boat (notice the "squeezed" portion in one of the photos), especially at the VERY narrow opening made at the factory to pass it from the AC unit into the wall cavity (maybe 2" x 6" in a long oval?). Couple these restricted flow areas with the 12K btu efficiency of the newer Marinaire unit installed by the previous owner, and no doubt the conditions are ripe for making the condensation being experienced. Especially since the duct inside the wall is ambient to the bilge air and not the conditioned air of the salon or aft cabin.

[Bubbastump13]

Source of the post I'd have to check but have you taken a look at what it would take to remove the mirror over the makeup table in the aft cabin? I think this would give you access to that area. You'd likely have to cut the wood panel behind it unless there is a removable one but it would get covered back up with the mirror anyway.

Looked into that, even going so far as to remove the mirror completely. There's a single 1/2" plywood sheet pinned floor to ceiling behind it, but its a forming face for the aft cabin only because there's a 2nd additional sheet of 3/4" plywood behind it that appears to be the inside of the wall pocket noted in the photos (that wall is the main cross support for the aft end of the flybridge). In other words, I'd have to cut through 2 separate sheets of ply. I thought about cutting it to form an access that could be removed and replaced, but too much work for the problem at hand.