Thanks for the response, sorry to respond so late but just saw it now.

On Feb 7, 5:27 pm, GaryO @ . 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?

Absolutely no idea whatsoever.

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.

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.

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
blocked.

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?

My hypothesis, without seeing the rest of the plumbing is the
following:

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.)

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 ******* 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
jammed in.

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 of the AC's condensate line.

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.