Can sewer gas get into the A/C system?

This is my first post to this forum, so thanks in advance for any help. I'm trying to figure out a strange situation in our house and hoping for some wisdom from the community here on which direction to go to start investigating the problem (is it a plumbing problem or an A/C problem?!).

So here's the problem: we've got an intermittent smell coming through the A/C system that I believe is a sewer gas type of smell. My wife says that it smells like rotten eggs (sulfur-like), and I think it smells like sewer gas. I know these problems are hard to nail down, so let me write a few observations:

- I'm almost certain the smell comes from A/C ducts. When it first starts appearing, I put my nose up to a duct and its always strongest there.
- It always starts up around 3:00PM to 5:00PM and then starts dying down in the evening.
- It appears to be related to how hot it is. It occurred first last summer, went away over winter, and reappeared recently (its starting to get really hot again now).
- It doesn't always happen. Today there is no smell, however yesterday it was really bad. The weather was virtually identical between the 2 days.
- The A/C condensor drip is not hard-piped to the sewage system (it just drips on the ground outside).
- The house is 13 years old.
- We have a 3rd bathroom in the back of the house. The shower in that bathroom is never used. Occasionally we get a dry-trap smell in that shower ... but that bathroom is nowhere near the intakes for the A/C.

That's the situation here. I can't decide whether to call out a plumber or an A/C technician. And with either one, I'm faced with the problem of "will it smell that day (of the service visit) or not?". I suppose its possible that the smell is not actually coming from the A/C, but it sure does smell strongest at the ducts. I also wonder if something is dead (rats? we had a rat problem a couple years ago) ... but the smell doesn't seem to be a decomposing animal type of smell.

Anyways, sorry for the long first post and thanks again for any advice y'all might have!

mystery smell??

you alreaady answered every questinon I was gonna ask you ...

no mice in the system rotting away,

no ac drain directly tied into the sewer?

no traps that are dried oout

probably want to get a ac guy out there first...next time it stinks.



could their be a pan under your heating -ac unit that might be holding water that gets stagnant after a while??

I had a drain that backed up on my a/c unit - it was a woody mold/fungus that had grown up and essentially blocked it...a little water was getting out, but not all. If you aren't concentious (sp?) about keeping the filter clean, or it doesn't fit well, you could have all sorts of junk on the condenser coil. I'd take a look at that first. Dust/hair/etc. caught on the coil would dry out and not smell in the winter, but would become nasty when the a/c was running.

cleaning ducts

their are companies that will come out and clean out your ducts.....


if you got old sewage down in there , the humidity might make

something funky happen once in a while...


most of the places around here are fly by night around here.....and charge too much.....


first check with the BBB in your area and see who is legit

and call them to sweep out the air ducts......

Thanks!

2 replies already, and its a holiday no less? Thanks for taking the time to help me!

Mark ... I'll check for a pan underneath the air handler.

Jadnashua ... I am good about maintaining the A/C. The handler/coils are pretty clean and the filter is changed regularly.

Sounds by your advice I'll call the A/C guy first. I've got a very trustworthy A/C tech that I know, and I'll probably get his recommendation for a duct cleaner type service.

I would not be surprised if it is NOT the A/C though. I say that because of the fact that the smell is intermittent. 1 day I'll get it, the next maybe not. I might have 3 good days in a row, then get hit for a week straight with it.

Just seems to me if it were a crap-inside-the-air-conditioner-type problem, it would be a constant type of smell, you know? I'm still thinking a plumbing problem, but I may give the duct cleaning a shot first.

Thanks again ...