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DennisH, Appliance Technician
Category: Appliance
Satisfied Customers: 198
Experience:  14 years with current appliance repair company
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How to get rid of bad smell from AC vent in home

Customer Question

I am having a problem with diagnosing a very distinct smell from one of the AC vent located in the living room of a home. When the AC is turned on, after 5 minutes, a smell like from the horse staple comes through only one (1) of the AC vent in the house. I hired a AC guy to come out to check on the AC, can't find anything wrong with AC. This vent sits on top of the sewer line. I had a plumber go into the crawl space but cannot find a leak in the sewer line either. The clean out is right outside this vent. The other vents in house doesn't smell. Does anyone have a clue as to what's going on?
Submitted: 9 years ago.
Category: Appliance
Expert:  DennisH replied 9 years ago.


If You are getting an odor from only one vent in the house something has either fallen, or crawled in and is now decaying if You are comfortable with disassembling the duct work yourself then You could find this item and clean it out.

If not there are companys that will clean ducts for You.

If You need more info feel free to ask


Customer: replied 9 years ago.
Reply to DennisH's Post:

Are you saying that there's a dead animal in the duct by the vent that is letting out the smell. Can a AC technician clean it out? Or do I have to hire one of those cleaning duct company to clean it. The reason I am asking is that I can have the previous AC company come back.

A friend of mine had said the same thing, a dead animal might have died. But he also said the smell would have gone away by now since we had this smell last year but the AC company that came out didn't bother to check on my system and needed to smell the odor before going any further. Since the smell was not produced right away, the AC guy left. And by then, the weather was getting cold, so the AC was not turned on again until recently.

This is a rental home and my tenants have turned the heat on last year but the smell didn't come through. Also, the smell took a while to come on last summer (maybe 15 minutes to 30 minutes), but this year, it took about 5 minutes for the smell to appear.

I want to give you all the facts to make sure we diagnostic it correctly.

Have you personally encounter this situation before in your line of business?

Can it be this as a friend just suggested:

The vent is drawing the odors from the sewer line due to reduction of air pressure outside. If I cover the sewer vent with a tied-on piece of plastic., completely shut off air around the sewer vent.......for a time while running the AC unit, would the smell be gone?

Or maybe, getting the pipe system cleaned out and see if possibly something is caught in the pipe since the air passing over it picks up the odors.
Many times, such odors occur in heating systems because dust and other particles over time get caught up in the pipes?

Expert:  DennisH replied 9 years ago.


Sorry for the delay I was having technical trouble.

If the smell is being pulled in to the system it would disperse evenly from all vents.

Just a wild guess here but the A/C uses High speed fan as where the heat would only use low speed if some how the vent pipe from Your sewage ran through the duct work( I have seen this before along with other things, cable, gas, and water lines) You could get enough pull to bring sewer vapors into the duct other wise its under pressure and would tend to blow out through any leaks in the ducts so it would not be likely a smell could be pulled into a single duct.

this is about the only thing I can think of other than something in the duct such as an animal, but then again that gets questioned since the smell only occurs when the A/C is used odors from items would tend to be more strong with heat.

I am going to have to say that there is likely a pipe that has been shortcut through the vent and the high speed fan is able to pull a vacum on this pipe and pull in odors.

Let Me know what You find