A/C drawing air up sink drain.

[ice2fire]

Whenever we turn on the A/C, it's just a matter of time before the whole RV STINKS.

It appears the A/C is pulling air up the waste pipes connected to the double sink. Under one sink there is a drain pipe that connects to the drain pipe that comes down from the other sink. Under that there is a P-trap. There is also an inside vent under the sink.

Why the smell ? Sinks are used all the time, thus water always in the P-trap.

Thanks for any suggestions.

[wa8yxm]

Though modern A/Cs do not usually have fresh air intake or stale air exhaust vents (I can tell you how to add them) some older models do.

More likely sceanaro. The "Stink" is there all the time, when you turn on the A/C you turn off and close the Fantastic Vent, thus the stink becomes noticable.

Air admittance valves are good suspects.

[Dave_H_M]

First thing I would do is take the AC cover off on the inside and look around up there.

Is the air output connected properly to the ducting or is it blowing some air into the area between the ceiling and roof like mine was.

Next I would take a bright flash light and see if the evaporator coils look like they are growing mold.

Also I would check to make sure the AC drain was working fine (not clogged) on the top. Water should be dripping off the back of the roof in warm weather when the ac is running.

I had a Ford pick up that made a nasty smell with the air on and it was a moldy evaporator coil.

Also Gene's idea is plausible, I think that could be run down by sniffing the individual vents/outlets.

On second thought, forget about all of the above that I suggested until you do a couple of things.

1. Use your sniffer and positively identify where the smell is coming from.

2. Before going thru all the gyrations about the kitchen sink, if the smell is coming from there isolate if it is coming up thru the P traps, if so it has to be bubbling. Then check the under sink air valve as described earlier, cap it off and see it the problem is cured.

3. Post back on your findings and what the smell smells like.

[2_many_2]

short kid wrote:
I would try wrapping a baggy over the air admittance valve and sealing it off. Then turn the ac on to see if you still get the smell. Just a thought.

Another good thought, please let us know what happens.

[MrWizard]

i would look at your roof
the exhaust air from the A/C unit might be blowing into the septic vents on the roof
change the vent caps to the Directional weather vane type

JUST a possibility

[short_kid]

I would try wrapping a baggy over the air admittance valve and sealing it off. Then turn the ac on to see if you still get the smell. Just a thought.

[Gene_Ginny]

Dead mouse in one of the AC ducts? :h

[2_many_2]

Old-Biscuit wrote:
A/C Unit can NOT pull any vapors thru water in 'P' traps....not going to happen

A/C Unit return air CAN pull odors from grey waste tank via the Air Admittance Valves under sinks on drain line downstream of 'P' trap.
OEM AAVs are just a thin flexible diaphragm held in-place by a 'tang' on diaphragm
Tang stretches...diaphragm doesn't seal off..stink from grey tank comes into RV.

Cheap ones available for $5 at Big Box Stores.....better ones/higher pricing also available.....

I replaced mine with these as suggested by forum members. The manufacturers web site is quite extensive explaining design and function.

[phays]

As already pointed out, check the air admittance valve under the sink.

Do you have basement a/c or roof mounted a/c? More likely to have this problem with basement air because of possible leaks in supply side duct connections.

It appears you do have an air leak to the outside from the supply side of the air conditioner. Air out the supply is equal to air in the return side. If air leaks out of the supply to the outside then the return side has to get the air someplace and the result is a negative pressure in the rv.

[Dutch_12078]

Old-Biscuit wrote:
A/C Unit can NOT pull any vapors thru water in 'P' traps....not going to happen

A/C Unit return air CAN pull odors from grey waste tank via the Air Admittance Valves under sinks on drain line downstream of 'P' trap.
OEM AAVs are just a thin flexible diaphragm held in-place by a 'tang' on diaphragm
Tang stretches...diaphragm doesn't seal off..stink from grey tank comes into RV.

Cheap ones available for $5 at Big Box Stores.....better ones/higher pricing also available

Just curious, but since RV A/C's are air recirculating devices where the inlet air volume exactly equals the outlet air volume, creating no negative or positive pressure, how does it draw air out of the AAV?

[Old-Biscuit]

A/C Unit can NOT pull any vapors thru water in 'P' traps....not going to happen

A/C Unit return air CAN pull odors from grey waste tank via the Air Admittance Valves under sinks on drain line downstream of 'P' trap.
OEM AAVs are just a thin flexible diaphragm held in-place by a 'tang' on diaphragm
Tang stretches...diaphragm doesn't seal off..stink from grey tank comes into RV.

Cheap ones available for $5 at Big Box Stores.....better ones/higher pricing also available

[eHoefler]

Remove the grill from the A/C and look up into it. Is the attic sealed off from the return??? You should not see any insulation or framing for the roof. If it is not sealed off completely, you can draw sewer gases through the attic from the sewers vents in the roof. The vent pipes are not sealed from the roof and just stick up just enough to be covered by the vent assembly.

[Kayteg1]

Than RV AC should not create vacuum. I would check for a cut in blower housing.

[doughere]

I would check the sink's air vent. This device is designed to allow air into the drain line (grey tanks smell just as bad as black tanks). If the vent flap is bad, it will allow air to exit the drain line into the unit. The vent just unscrews to remove it.

I once had a problem similar; it turned out the tank vent line through the roof wasn't well sealed, and stinky air was entering through the cracks. Stuffing fiberglass in the cracks solved that problem.

Doug

[naturist]

(a) perhaps the inside vent under the sink doesn't seal properly. They contain moving parts and although they are supposed to last forever, they don't.

(b) you may need to adjust the air flow through the AC. Perhaps it needs some air door opened or closed a little more?

(c) maybe you could leave one of the windows over the sink cracked a little bit to relieve the pressure.