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Old 08-10-2018, 05:54 PM   #1
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When ac is running the rv smells like black tank

We have a 2018 cck with 2 acs and have noticed when the acs are running there is a smell of the black holding tank throughout. Any ideas why? is the ac sucking in air from the tank vent?
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Old 08-11-2018, 04:45 AM   #2
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You most likely have an air admittance valve leaking by. They're located under sink and lavatory cabinets near the top.
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Old 08-11-2018, 10:48 AM   #3
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It is also possible that your roof vent for the black tank is located near an AC unit, which may be pulling the fumes from the vent back into the RV through the AC.

There are alternatives to the stock roof vents available.
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Old 08-11-2018, 10:55 AM   #4
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The AC doesn't pull air from outside it recirculates the air inside and is supposed to be sealed from all outside inputs. Just like at home.
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Old 08-11-2018, 12:20 PM   #5
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if your smelling something in your unit with the A/C running, then the odor is coming from inside the unit.
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Old 08-11-2018, 12:39 PM   #6
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Are you sure?

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Originally Posted by JohnD10 View Post
It is also possible that your roof vent for the black tank is located near an AC unit, which may be pulling the fumes from the vent back into the RV through the AC.

There are alternatives to the stock roof vents available.
The RV air conditioners I've looked at don't seem to be designed to pull in any fresh air; should just recirculate. If they drew in fresh, hot air, it would take even longer to cool the RV down.

There's always the possibility of a little leakage of course. For example, a bit of air could leak through the drain port on the evaporator (which is in the path of inside, circulated air).

My vote is for the the under-sink air admittance (vacuum breaker) valves.

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Old 08-11-2018, 12:44 PM   #7
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Originally Posted by JohnD10 View Post
It is also possible that your roof vent for the black tank is located near an AC unit, which may be pulling the fumes from the vent back into the RV through the AC.

There are alternatives to the stock roof vents available.
I have heard of this happening more than once...

So it is a distinct possibility.
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Old 08-11-2018, 01:41 PM   #8
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I have a 2015 FR Cardinal. I have been experiencing the same thing. I replaced both my under counter vents and still have this problem from time to time. I have tried all sorts of chemicals for the tanks. I am going to change out the stock roof vents with the 360 vents.

I live in Phoenix and the temps have been really hot. Im thinking that the chemicals arent rated for this freakin heat.
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Old 08-11-2018, 01:55 PM   #9
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Might try to put a stopper in the bath tub/shower and sinks in the bath and kitchen. If it goes away you know where to look.
This is also assuming the air admittance valves are functional
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Old 08-11-2018, 01:56 PM   #10
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Add some perfumed liquid to the black tank and run the AC’s to verify the odor is black tank odor and not mold odors coming from the AC’s themselves. Mold can smell just like poo. If the source of the odor is from the black tank and it can be the gray tank too as they can get quite stinky! The AC’s units are leaking indoor air to the outside of the coach and holding tank air is coming into replace the air the AC’s pump out through leaks in the AC’s or leaks in the roof ducts. It is best to find and fix the external leak of the AC. Under counter plumbing vents can be a source of odors as well as the commode as it is open to the holding tank. Unless the roof plumbing vent is plugged, there is not a roof plumbing vent made to stop negative pressure in the coach from pulling in makeup air. If the AC units themselves are molding inside, they will need to be cleaned to destroy mold growth. One problem with AC’s that shut off once the thermostat is satisfied, is the evaporator coil stays damp and becomes a source for mold and mildew to grow and thrive. It is best for the AC fan to stay running and dry the moisture from the evaporator coil to prevent mold growth and odors.
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Old 08-11-2018, 03:04 PM   #11
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Pull down the ceiling panel to the a/c. Check up in the opening and look for any openings in the tape around the duct from roof to ceiling . You can pull air from the “attic “ area and if the tank vent tube does not project fully through the vent base enough to seal odors can drop into the roof space and be pulled into the return air space.
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Old 08-11-2018, 03:20 PM   #12
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Look for mold.
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Old 08-11-2018, 04:07 PM   #13
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I had the same unpleasant experience happen to me one time. At a state park in Indiana last year. It was a warm humid day and I was running my air conditioner. The smell was a sulfur smell not unlike the smell eggs can make. But much stronger. My first suspect was the air conditioner because it seemed to be coming from there. Long story short, it was the water I filled up with at the state park. My theory is that the high sulfur content of the park's water reacted with the anode in the hot water tank. As stated before, the AC fan was pulling this foul air from somewhere. I confirmed the probability of the water having a high sulfur content with my brother-in-law who has drilled wells in the area. I later docked at his house and replaced the water in my tank with soft water. No problems after that. It has not happened since. I do have an onboard carbon filter, but this did not seem to help with the suspect water.
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Old 08-11-2018, 04:52 PM   #14
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If you've never encountered this...

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I had the same unpleasant experience happen to me one time. At a state park in Indiana last year. It was a warm humid day and I was running my air conditioner. The smell was a sulfur smell not unlike the smell eggs can make. But much stronger. My first suspect was the air conditioner because it seemed to be coming from there. Long story short, it was the water I filled up with at the state park. My theory is that the high sulfur content of the park's water reacted with the anode in the hot water tank. As stated before, the AC fan was pulling this foul air from somewhere. I confirmed the probability of the water having a high sulfur content with my brother-in-law who has drilled wells in the area. I later docked at his house and replaced the water in my tank with soft water. No problems after that. It has not happened since. I do have an onboard carbon filter, but this did not seem to help with the suspect water.
People who have never encountered high-sulfur water just won't believe it can have such a strong odor. We were stationed in southern New Mexico (Las Cruces) for two years in the early 70's. The town had five wells, three of which weren't bad and two of which had high sulfur content. We lived in a two-story townhouse. When I entered the house on the first floor and DW was taking a shower on the second floor, I could have sworn someone was scrambling eggs in the kitchen.

It's easy to see how you could smell this odor (and not recognize it as sulfur) if you were in a densely-packed campground and someone was watering a garden or washing a dog/kid/trailer or using a swimming pool nearby. Anything that atomized (misted) the water would do it.

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Old 08-11-2018, 08:27 PM   #15
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Check your air admittance valves first, then open up the air conditioner. If it runs air through vents, check those too!! Something may have crawled in there and croaked.
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Old 08-11-2018, 10:50 PM   #16
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Quote:
Originally Posted by carlknowles View Post
We have a 2018 cck with 2 acs and have noticed when the acs are running there is a smell of the black holding tank throughout. Any ideas why? is the ac sucking in air from the tank vent?
Without ac running but the vent over the stove running or the fantastic fan running, do you smell holding tank odor?
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Old 08-11-2018, 11:45 PM   #17
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Originally Posted by JohnD10 View Post
It is also possible that your roof vent for the black tank is located near an AC unit, which may be pulling the fumes from the vent back into the RV through the AC.

There are alternatives to the stock roof vents available.
The RV roof AC does not draw air in from the outside. It only recirculates the inside air. Your house AC works the same way. Auto AC can draw in outside air.
the smell is coming from an air admittance valve under a sink in the coach.
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Old 08-12-2018, 03:53 AM   #18
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Quote:
Originally Posted by chapelt View Post
if your smelling something in your unit with the A/C running, then the odor is coming from inside the unit.
When was the last time you took the cover off the AC unit and cleaned the coils and the drip pan?

Im guessing the answer is never.
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Old 08-12-2018, 06:25 AM   #19
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We had this issue with our 2017 Cardinal and I was advised (by someone in this forum -thank you) to get on the roof...pull the vent covers off by removing a small Phillips screwdriver and use the expanding foam spray insulation AROUND the vent pipe. Replace the vent cover and put a dab of silicone to seal the screw back in and you're done.

I did - problem solved.

While the outside AC units may not pull air in from the outside...the odor can escape from the vent tube then be pulled back between the roof and insulation and get into the AC's return air that way.

I added spray foam insulation around ALL of my vent pipes and we haven't had the problem since.


Here's another thread on the subject: http://www.forestriverforums.com/for...l-73081-2.html
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Old 08-12-2018, 08:30 AM   #20
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Haven't had the problem, but interested in what you find. First trick would be to use anti stink in the holding tank, but wouldn't do that until you find the source of odor penetration.
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