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Question DetailsAsked on 10/7/2015

A bad smell circulates in my house when I turn on the AC, but goes away when it is off - what should I do?

The AC is over 10 years old - has recently been serviced. I live in a three story town house. the second story is the main floor and the ac vents are on the floor. the worst smell is by the stair case leading to the third floor which is by a floor vent as well as in the garage which is located on the ground floor. The smell is kind of sour - not really musty. Again the smell is in the main floor (second story) mostly goes away when the AC is off, but remains in the garage (ground floor).

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1 Answer

Voted Best Answer

I am guessing the places it smells the strongest (garage) is the closest to the A/C evaporator - either in an independent A/C system air handler, or installed in your heating ducts if a central air system.

IF a sour smell rather than a rotten meat or dead animal smell, most likely "stinky sock syndrome" - mold and bacterial growth on the air conditioner heat exchanger or a swamp forming in your evaporator catch pan.

If the evaporator was cleaned as part of the A/C servicing and is still clean, then could be a general moisture accumulation issue in the ducting, where the dust accumulation is forming mold or fungus.

Either way, Heating and A/C contractor would be your Search the List category - though if the A/C service did not include at least inspection of the evaporator at your recent servicing then time to get a new HVAC technician, because mold and mildew and fungal growth on evaporators is one of the top HVAC issues.

Other possibility is rodents living in the ducts and you are smelling urine smell - though usually if you had a family living in there you would be hearing them scurring around in the ducts too.

There is a remote poissibility it is a rodent smell or fungal rot of wood due to a slow water leak, AND it is pulling that smell into the A/C system through a duct gap or at the furnace/air handler - though normally if a fairly strong smell in the ducts you would smell lit directly at least close to the leak point. Some determined sniffing might be in order to see if you can track down an exact location.

Answered 4 years ago by LCD


Answer #1 is thorough. I agree. One more point.You may need the services of an environmental specialist to check for mold if the HVAC contractor is unsuccessful in locating the source of your problem.

Source: Poppy Ross

Answered 4 years ago by PoppyRoss

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