View Full Version : Terrible smell from my ac units
05-23-2004, 12:18 PM
(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.
05-23-2004, 01:05 PM
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.
05-24-2004, 10:45 AM
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.
05-24-2004, 10:50 AM
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.
05-24-2004, 02:15 PM
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.
06-04-2004, 11:22 PM
you mught have a heat load calculation done to see if the units are oversized as well as caulking windows, insulating properly, etc...
06-05-2004, 10:57 AM
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.
06-05-2004, 11:03 AM
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).
06-05-2004, 10:04 PM
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
06-05-2004, 11:03 PM
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.)
06-06-2004, 08:10 AM
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.
06-06-2004, 02:46 PM
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.
06-06-2004, 05:53 PM
once you have mold it is everwhere...cleaning it just starts the process all over
06-07-2004, 05:11 PM
The conclusion that I am coming to with your help is the following.
1. Replace the evaporator coil.
2. Contact a lawyer to determine what my liability for this is after the house sale goes through.
3. Based on the lawyer's advice, inform the new buyer about the situation before the closing goes through.
What I don't want to end up with is a large bill for the system AFTER I have sold the house.
I am concerned that replacing the coil will not solve the problem as the terrible dead animal smell is not a general smell, but only comes from a few of the vents. There is a general dirty sock smell which comes from all the vents sometimes, but the really terrible smell is intermittent and comes from the vents where I have already replaced the piping.
What a hassle! I really thought that we had solved the problem last year!
06-08-2004, 08:48 AM
I've decided to
1. Get a mold remediator company to investigate what type of mold I have. (At least I now know that it is most likely mold - up to recently, we all thought the most probable reason was a dead mouse or some thing similar due to the type of smell) Also to determine why I get the problem on only a few vents.
2. Get the coil changed on at least the upstairs unit.
(I'll see what the remediator says about the downstairs unit)
3. Speak to a lawyer
4. Tell the new buyers today about the situation asap.
5. Determine if the units are sized correctly? Why would the smell have reoccurred on the new pipes - must be a reason.
Anything else I have overlooked?
06-13-2004, 10:39 AM
Replaced the coil on the upstairs unit - could see nothing wrong with it.
Had the ducting cleaned and biocided - only found a slight whiff of mold in the return plenum and nowhere else, However, this is now totally clean so there should be no re-occurrence.
On the downstairs unit, had everything cleaned and biocided - coil was clean, found a little mold or whatever on the fan motor in the unit, plus the insulation was a little wet on the floor of the air con unit, from where the drip tray had been overflowing before I corrected the poor drain. Otherwise found no problem.
Having spent a third of my month's wages, on coil replacement and biociding, I think that the new owners can rest in peace. I have also informed them of the actions that I have taken through my real estate agent and am waiting to hear their response.
Thanks for all the help folks.
06-20-2004, 12:55 PM
may want to look into a dipped coil trane usually offers them but you have had someone try to clean it three times
06-20-2004, 02:03 PM
The new owners have taken possession, though the smells continued to occur. I provided the new owners with the company name that had carried out the biociding and they will get in touch with them if they want to do so.
I think that the smells are probably due to mold spores occurring in the ducting, BUT, when the ducts were cleaned out, they were found to be very clean. So who knows? The biociding company was going to treat the ducts with a far more powerful chemical, approved by the FDA, which means you have to be out of the house for six hours or more.
Anyway, it is up to the new owners now, and I can sleep at night, as I have fully informed them as to what has occurred.
Thanks for the help
09-01-2004, 10:41 PM
I have run into this problem a few times, and replacing the evaporator coils solves the problem as far as im aware (10+ years old and above or a nice coil pull/acid cleaner powerwashing if below). Just thinking about it over the years, and learning new things everyday has brought me to a few other possible causes. What if you had the panned returns running up stud walls and those notoriously leaky returns were pulling air from a section of wall (or attic) that had saturated fiberglass insulation? Think it would smell, add humidity to the living space? Why does it get stronger when its very humid or even after a rain?
The possible answer and root cause of the problem MIGHT just be leaky return ductwork sucking in outdoor air through dirty, now wet, fiberglass insulation that has acted like a filter for years.Ever smell dirty wet yellow fiberglass insulation? Smells like dirty soxs to me,especially in high humidity situations.
I just had a house today with the same problem. Brick one story Chicago Bungalow (no wall insulation on walls, but wall cav return runs not top blocked running up walls to the attic plate). Smell used to happen only when ac was on ,not when "fan only" was on. Now, it happens all the time.We're replacing the 2.5 evap tomorrow. will keep you posted.
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