Sewer Smell when running AC

[gtippett]

Hey Everyone,
When we run the AC for a few hours, we get an sewer odor within the unit. Anyone experience this in the past.

Thanks,

[Jlawles2]

By chance are you attached to the campground sewer with the valves open? Try closing if so.

The other issue could be the AAV (air Admittance valves). There are 2. one in the bathroom vanity at the back almost to the counter top and the other in the island again up high. Both are on the sink drains (follow the plastic pipes from the drain to the TEE then UP.

I replace both of mine with the https://www.homedepot.com/p/STUDOR-R...0353/203111264 (avoid the larger as they may be too large in diameter and contact the walls). Both of mine were less than hand tight and I was actually surprised they had not rattled out.

The only other thing could be mold in the AC. Once the mold gets wet from the condensation on the condenser it can start to smell. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 is a good cleaner. Add the brushes https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 and fin comb if you think deeper cleaning is needed.

[Jkwilson]

This is not an uncommon post on all RV forums. I wonder if it could be related to the black tank flush system. Here is my reasoning:

The air conditioner neither draws in outside air nor exhausts inside air outdoors, so the smell can’t come from the outdoor part of the vent.

All normal paths from indoor space to the black or gray tanks are supposed to be sealed via P-traps, duck bill valves or AAVs.

The anti-siphon valve is located in an interior wall space which may be connected to the duct space of the air conditioner or the air space between the coroplast and the floor creating a potential path from black tank to indoor air.

The anti siphon valve admits air to the hose connection side of the black tank flush when not pressurized. When pressurized, the valve compresses a spring, moving the seal which opens the path to the tank and closes the path to the air. If the seal on the tank side failed or there was debris on the gasket, it’s possible for there to be a path from black tank to air inside the camper when water pressure isn’t present.

Certainly speculation, and an empty trap, failed AAV, damaged vent pipe or otherwise compromised drain could also be the culprit.