What could a foul odor coming the ac vents be

Question

What could a foul odor coming the ac vents be

Answer 1

OMG!  We had the same problem in out first house.  It only smelled when the ac was on.  Very musty & sour.  We couldn't figure out what it was, but the house wasn't taken care of before we moved in & we had done a lot of renovations.  

We finally couldn't take the smell anymore and hired a Vent Cleaning company.  We recieved a mailer that had a coupon, so we called them.  They ended up vacuming out 9 lbs of dirt and debris from my vents (my house was only 1200 sq ft & about 55 yrs old).  They also disinfected and deoderised the vents and the smell went away, never to return.

Well worth the money.

Answer 2

Dirty water.

Answer 3

Dead critter, mildew, mold, something being pulled into the system from the attic ducts

Answer 4

possibly excess mold either in the supply air plenum, or the evaporator coil. Or depending on where your equipment is located, you may have a dead mouse in your ducting somewhere. If you have flex-type duct work running in a confined crawl space such as the attic or under the house, or through a dedicated chase, behind a wall, then it is not uncommon for mice or little squirls to eat their way through the outer jacket of flexible type ducting and get inside. Once inside they'll make nests, or get lost and just die in there.

As an a/c tech I have responded to calls where a foul smell was coming from the vents and sometimes i did find dead birds, rats or mice. This was especially prevalent where the heater was in a hall and the RETURN AIR side of the heater was drawing from under the home or structure.

Goodluck

goodluck