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.