I've posted this problem a few times over the past year, but still no
luck. But maybe fourth time's a charm, and I've learned some things
since my last post...
When I run the kitchen sink, and the AC kicks on, I get a bad smell
throughout the apartment. If I run the kitchen sink, and the AC is
off, I get the same smell, just much fainter. I put a cork in the
pipe where it enters the drain pan, and run the kitchen sink and AC,
and got no smell at all. So I'm guessing it's coming from the drain
line. It's of varying strength, and I don't know if it's sewer gas or
not, but it's definitely unpleasant.
I had a plumber open up a wall next to the AC unit. There's a
separate condensate line, and he found where it came out in the bottom
of my building.
While I could possibly understand maybe I'm getting a bad mold smell
off the condensate line, what I don't understand is why it only
happens when I run the kitchen sink.
Yep, there's a trap, though not an especially large one. I posted a
pic of it at:
I'm trying to figure out if there's a way to somehow intentionally
empty the trap so I can see if the smell comes without having to run
the kitchen sink.
But while I can understand how pressure differences caused when the
kitchen sink runs could suck water out of the p-trap, I don't
a) how this connects to the condensate line, as I thought those were
separate from any line the kitchen sink would connect to, or
b) what exactly the smell is from, as absent a serious mold problem a
condensate line shouldn't smell like much of anything (as I understand
Here in Florida where it doesn't freeze, we just run them outside.
But up north or in big buildings, you find them plumbed into the sanitary
Aside from obstructions, incorrect designs are a problem. The condensate
connection may be an afterthought, and improperly vented, while the rest of
the house is OK.
It's possible to connect up flexible clear vinyl hose, at least
temporarily, to see inside the line and diagnose what's going on, whether
the trap is siphoning.
I'm in Florida too but the pipes can't run to the outside of the
building here (by county ordinance I believe). The condensate line
runs down to the bottom of the building, so I don't know if/why they
would be attached to the sanitary drains. I thought that was against
I'm fairly certain the building was built without air conditioning
originally, so that's entirely possible.
I figure it has to be, since the smell doesn't appear if I cork off
the condensate line.
On 3 Feb 2007 13:06:43 -0800, email@example.com wrote:
I'm trying to make some sense of what I'm seeing in your photo.
Perhaps you can clarify some items.
What is the curved black line which comes from above and looks to
connect to left side of the trap?
I think I also see, above the left end of the trap, an automatic vent.
If so, these are prone to failure and often cause a sewer gas odor
problem. I'm puzzled why it is in this location, as it should be on
the sewer side of the trap.
I'm in the northeast, and overhead AC systems may be different in FL.
Here, when systems which are mounted above finished spaces, they are
normally equipped with two completely separate drain lines. The first
is the normal condensate line. The second is a backup line connected
to a drip tray placed under the AC unit incase the first line becomes
My hypothesis, without seeing the rest of the plumbing is the
1) The roof vent pipe for the kitchen sink is obstructed, perhaps by a
bird or bees nest, or?? (The kitchen sink may not even have a proper
vent - the quality of the plumbing in your photo does exactly give me
a good feeling that it is plumbed correctly.)
2) When you run water in the kitchen sink, it is drawing vent air
through the automatic vent by your AC unit. It will also suck all the
water out of the trap on the AC's condensate line.
3) Now you have a clear path from the sewer line right into your AC's
intake air suction side.
4) Honey, what's that smell?! :-(
Thanks for the response, sorry to respond so late but just saw it now.
Absolutely no idea whatsoever.
That's just a cap a plumber put on when that pipe got clogged. It
just unscrews, and I'm supposed to pour bleach down it once a month or
so to keep the pipe clear.
Hmm I thought all the condensate would be produced by the evaporator
coil, the surface of which would just drip into the pan. There's
another line going to the drip tray?
I think this was it. The funny thing is the reason I finally checked
this thread again was because today I tied some twine to a small
flashlight, climbed onto the roof, and lowered the light down the vent
pipe. There was some sort of obstruction about 5 feet down, so I kept
dropping the flashlight onto it until it went down further; I couldn't
knock the stuff completely clear but it's well under my unit now so
let's see if that works.
Obviously I don't want to be a complete bastard and make it my
downstairs neighbors' problem, but since this should be the common
area of the building maybe I can get the building to pay for a plumber
to snake the whole vent. Or is there anything I can do myself to clear
this? Drano? The stuff looks like some sort of mix of paper,
possible rust chips and who knows what else.
Your estimate of the quality of plumbing in my place is right on the
money. I have had repeated problems with every drain, sink, and
faucet in the place. Just last week one of the drain lines underneath
my sink fell apart. Apparently it wasn't screwed in or anything, just
Well it's not an automatic vent so probably not that, but I'm sure
you're right about it sucking the water out of the AC trap. I think
the trap's not deep enough also, but the last plumber told me anything
bigger would have to be installed in the wall.
On 24 Feb 2007 14:06:35 -0800, firstname.lastname@example.org wrote:
Looking at your photo again, I think it may be the freon lines. There
looks to be insulation wrapped around them.
I don't know about your particular setup, but often there is a tray
under units mounted in an attic to catch any water which may overflow
the pan (perhaps due to a plugged drain line) and direct it safely
If you get a flashlight stuck in the drain line and you are in for
even bigger problems!! :-(
OK, try this. Install an automatic vent between the AC trap and the
sewer line. Here is a link to one (just the first one I googled up):
http://www.idealtruevalue.com/servlet/the-55484/Detail They come in
different sizes, so select one appropriate to your pipe size.
You will need to cut a "T" into the line and install it on the "T".
You may want to add a short length of pipe to raise it 6-12" or so
above the "T".
This is a one-way valve which allows air to be sucked into the line,
but not out. It should prevent your AC drain trap from being sucked
That could be it. A similar looking tube comes out of the roof and
attached to the condenser unit.
That's what I think this is. The drain line was clogged once and kept
spilling water into my hallway from the tray.
There was one heartstopping moment when it got stuck. Fortunately I
got it out.
Wait, I thought you said automatic vents were subject to failure? But
I'll give it a shot, considering it's 4.99 I could at least order it
in case I need to use it later. Unfortunately I can't tell if
clearing out the vent pipe fixed the problem, because coincidentally
one of the kitchen drain lines came loose and I can't run the kitchen
sink to see if the smell problem is fixed. If it's not I'll
definitely try the automatic vent.
On 26 Feb 2007 17:05:55 -0800, email@example.com wrote:
They do sometimes fail and cause odor problems, but then you just
replace them. They're cheap. If it has a threaded fitting, you can
just screw the new one on. They are commonly used in places like
island sinks where it is not possible to run a standard vent line up
to the roof.
I don't know if this one is the correct size for your piping. Better
to go to a hardware store or HomeDepot/Lowes and look at their
selection. You will also need to cut the existing pipe (hacksaw) and
glue in the "T" fitting. From the looks of all the existing
couplings, etc, I'd replace about half of it rather than try to adapt
to it - probably easier in the long run.
Oops! Now you probably have an odor problem under the kitchen sink!
This is generally standard plumbing, unless it has been hacked up like
your AC drain lines. Again the hardware store has all the necessary
trap and drain lines for this along with the sealing gaskets -
typically a kit with everything in it. Cheap stuff and often easier
to replace it than to reuse the old.
Actually, as my AC problems gave me a deep awareness of the importance
of P-traps, I've been keeping it full by trickling a little water into
the left sink, of which the drain line is still intact.
I bought a section of PVC pretty much identical to the part that came
off, then got some PVC cement and tried doing it myself. Worked at
first then when enough water was going through it it came out again.
I figure I probably should just bite the bullet and spend 100 bucks on
a plumber to be safe.
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