(I posted this under residential and then found that there is a column for air quality, so I have copied the same message to here. -Apologies for posting in wrong place.)
Please help. I am getting a terrible smell like a dead animal from both my air-conditioners. This has been occurring on and off for the last five years. It only happens in the summer when it is hot and humid.
With my three ton Trane gas heat air-conditioner, the smell occurs when the unit is working and can be smelt in one or other of my sons bedrooms.
Last year I engaged a mould specialist to tell me what to do. He stated that I should just replace the piping and boxes to the rooms that are affected.
I replaced the piping and the boxes, and for good measure, also replaced the supply plenum and sucked all the debris and water out of the bottom of the air handler.
The smell still reoccurred. I then sprayed the coils with a mixture of bleach and water and this seemed to solve the problem. However, by this time it was late autumn and the hot season was almost over.
This spring the smell started again. I sprayed the evaporator coils again and also poured a cup of bleach into the bottom of the air handler. This worked for a week and then the smell started again last night. What can I do?
My two ton unit on my ground floor smells terribly when it is not blowing/operating. The smell comes from the return pipe. This also occurs when the weather is hot and humid.
The mould specialist told me on this unit that all I had to do was seal a small leak in one of the plenums and that this should solve the problem. This seemed to work the last year, but this year the smell has started again and it is really terrible.
Any suggestions will be highly appreciated. I have no recourse to any of the actions that the mould specialist suggested, as he is a friend of a friend. Also at the time he was here, the units were not smelling. Thus I am really on my own with this one. I also have just sold the house, and the new owners take occupation with in three weeks. Therefore I need to take action really quickly.
That sounds like what we call "dirty sock syndrome" or "DSS" for short.
Use the search function at the top of this page and type in the terms above in quotes.
Theres a ton of discussion here on that subject.
We've been doing so much,for so long,with so little, that now we can do almost anything, with nothing at all.
"short term fix"
Ducts with wet coils grow biologicals during the off cycle. Operating the fan in the on mode dries off the coil and ducts when not cooling. This makes the home more humid but stop growth in the ducts. A few contractors are operating the fan in the "on" mode and using dehumidifiers for humidity control. This provides max indoor air quailty and comfort. Might be a short term fix for "smells". If you go all the way target <50%RH.
Eliminate all odors from A/C coils by adding a high powered UV Light just down stream from the coil, to bathe the condensate tray in the light. It will kill the stuff that grows there and prevent the odors.
If the tray is a plastic material, try to place the light 24 inches away, or line the exposed area to prevent exposure. UV degrades plastic over time.
Thanks, that's a good point about the plastic.
Have seen/smelt goodies drawn up thru sewer in basement floors near returns of air handlers.
you mught have a heat load calculation done to see if the units are oversized as well as caulking windows, insulating properly, etc...
Found mold in the coils of the 2 ton ac, and cleaned this out, plus sprayed it with Chlorine dioxide. I also got the condensate drain working again, so that should solve that one for the timebeing.
The 3 ton unit coils were totally clean and shiny, so I have no clue where the smell comes from, as I have replaced all the piping downstream, the plenum, distribution boxes etc. I looked at both sides of the coil, the drain pan is dry, and there is no evidence of mold anywhere.
I am now spraying chlorine dioxide into the return vents on a day by day basis and hope that this will solve the problem.
Sizing for house is fine, 2 ton unit for 1250 sq ft, and 3 ton unit for 1750 sq ft. all windows caulked, though weather strips missing on most windows, however, when the windows are closed there is no gap between them. (The locking mechanism pulls the windows together).
the best attack on any smell is to first lower the humidity to 45% for one week with a central dehumidifier and see if it goes away ..this works for most problems except DSS
I hand the house over in a week to the new owners, so will just have to hope the daily spraying with ClO2 works and kills enough of the mold or whatever it is, that the problem does not re-occur.
The smell only comes when it is hot and humid. It has not smelt the last three days, as the weather has been unseasonably cool. (And hopefully because of my spraying.)
As you leave your home, position the thermostat to the fan "on" position. The constant air moving through the ducts will keep the "air moving system" as dry as possible.
I opened up the 2 ton unit and found mold on the coils which I washed off with cleaner, and also sprayed Chlorine dioxide on to the coils plus surrounding area. This has solved this problem for this 2 ton system.
(by the way, the spray sold at air conditioning stores for this purpose is 99.5% water and .5% chlorine dioxide - it also costs an absolute fortune!!!)
However, the coils on the 3 ton unit are spotless - I looked at both the inlet side and the outlet side. Poured cleaning fluid on and sprayed chlorine dioxide (0.5% solution) on to the coils.
So, the coils are clean, the tray underneath is scarcely damp as all moisture drains off straightaway, (none drips into the drip pan underneath), the piping downside to most of the rooms is new (especially the rooms that smell the worst), as are the plenum and boxes.
However, I am still getting a terrible smell every so often when it is hot, mainly from the rooms that all the ducting has been replaced to.
Could the mold be on the return side before the coil??
Any ideas?? It must be mold as the mold on the 2 ton unit smelt the same as the smell I am getting from the 3 ton unit. I have not replaced all the runs of ducting or had it cleaned professionally - this could be a possiblility??? One of the rooms that the ducting has not been replaced to very occasionally smells. The worst semlls are from the rooms where the ducting has been replaced. I helped do this job, so I know that it was all replaced properly.
I have been spraying chlorine dioxide into the returns every day for three days now, but this has not stopped the smell from re-occurring.
What would you do??? The new owners take occupation in a week.