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Pokemon · 12-14-2015, 10:19 AM

I had been trying to chase down a holding tank type odor for some months now and found that when an exhaust fan is running with the coach mostly closed up (or negative pressure inside) there is a holding tank type odor coming from the air conditioning duct vents only on the driver side. About six vents in all. The MH is a 2005 32 foot Dolphin LX. We do not have the roof HVAC system. We have the basement type with the ducts in the ceiling. I am no stranger to plumbing, but for the life of me cannot figure a holding tank/HVAC cross connection here. Any suggestions. Thanks...

dpinvidic · 12-14-2015, 11:02 AM

JUst some point to consider.
On my tiffin, the AC intake vents ar on one side, and the output vents are on the other side. So it makes sense that the oder would just come from one side.

A common rule is that you should not FLUSH your toilet with the exhaust fan on...but your not flushing.

It just sounds like you might have a broken vent line in the holding tank (some have seen this inside the wall).
Then the general negative pressure pulls it into the coach.
And the A/C sucks it in, and distributes it to all the vents on one side.

A few folks have had tanks replaced (or dropped). During the process, the roof vent line became disconnected inside the wall and left that way.
Is your roof vent line behind the fridge??

Regards,
Dan

1bigmess · 12-14-2015, 11:06 AM

Something nasty growing in your AC vent or ducts? Could smell like a holding tank.

Pokemon · 12-14-2015, 11:17 AM

Thanks for the replies. Presently going to inspect the duct full length inside and the integrity of both tank vent lines for starters. Will post the results.

legryz · 12-14-2015, 12:29 PM

Pokemon, I had a similar problem but the smell was coming through passenger side vents near the refrigerator. I found that National didn't seal the hole they drilled for the vent to pass through the roof (under the vent caps) allowing gases to be drawn into the coach from the vent. I also found that the, expanding foam they used around the vent to tank hole, wasn't a complete seal. I dug as much out as I could and re-sealed.
Here's a couple pictures of the vent on the roof.
As you can see they didn't do a good job on drilling the hole where it needed to be.

Pokemon · 12-14-2015, 07:25 PM

LEGRYZ Thank you Thank you for the pictures. I think you nailed it. I took off some of the duct louvres and looked inside the driver side duct and could not see anything that might have died. But I did see where they joined up two pieces of duct rather sloppy and the joint is near the shower vent. Thanks to your pictures, I now think the fumes are going down around the drain line into the roof space and migrating into the duct through the loose fitting joint. With the roof vent running and pulling a negative inside the coach, I can see where this could easily happen. We spend our winters in Mazatlan and the roads down here the last couple of winters have been rough. Any movement could have worried out the insulation they used to seal between the vent and roof. I will pull the roof jacks off both vents to see if I have the same problem…B

Pokemon · 12-16-2015, 05:37 PM

LEGRYZ Pulled the roof jacks and I did have an oversize hole for the vent line on the driver side. The vents pipes were not broken. I used kwik foam to seal the annulus between the vents and roof and that seems to have fixed the odor problem. Thanks again for the pictures. Being a member of iRV2 has paid off again.

legryz · 12-16-2015, 05:42 PM

Glad I could help with your smelly problem, hope it stays fixed.

0rion · 12-16-2015, 05:45 PM

I was thinking maybe you had mildew in the ducts themselves. Maybe not though. If it persists you can turn a/c on and spray lysol into the intake and that'll help a lot with mildew in the vents. I do that about once a year on my truck.

Pokemon · 12-18-2015, 03:36 PM

LEGRYZ Did you use a can of spray foam to seal the vent line to roof? I used that product and it sealed good, but just now had an afterthought. Going down the road, if there is vertical motion between the roof and vent, maybe I should have used a release on the pipe such as silicone spray, wax paper or saran. I wouldn’t want to grab the vent line solid with foam and start a crack at the tank.

legryz · 12-18-2015, 05:30 PM

No I didn't. First I used some fiberglass insulation to fill the big gap then used self leveling RV sealant to cover the fiberglass. Reinstalled the the cap and sealed that.

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Don't have a picture of the SL Caulk over the fiberglass.

Pokemon · 12-18-2015, 06:02 PM

LEGRYZ: Thanks for the pics… That’s a better way to go. Looks like I will remove the caps again and hacksaw between the foam and vent and use caulk for the gap. More flexible that way. Always loved scraping off caulk and reapplying it. Better than repairing a possible cracked joint at the vent to tank later on.

craka · 01-13-2016, 01:09 PM

Fighting the same battle with my Seabreeze... I will give this a shot this weekend. Thanks!

Pokemon · 01-13-2016, 03:10 PM

I used quick foam and after it set up, I was concerned about the foam seizing the pipe and preventing vertical movement. So I ran a hacksaw blade between the foam and vent pipe and used a thin amount of silicone to finish it off. Above in this thread you can read where LEGRYZ used insulation and caulking. Good Luck with it...