Stinky furnace air conditioner

Our heating and cooling forced air system initially emits an odor after sitting idle for a couple of days. The house is 40 years old; furnace and AC replaced 10 years ago. If the AC is off for a day or two it has a musty smell when first turned on requiring all the windows to be opened for about half an hour to clear. We cleaned all the registers, removed and cleaned the blower, put bleach down the drain line, removed the de-humidifier and vacuumed out the plenum. The insides are dry, drip pan is dry and clean and the coil looks relatively clean. We also replaced the electronic air filter with a dry paper type. The smell is emitted from each register yet we could see no evidence of any mold growth and could not smell any unusual odor when the furnace was first opened. The smell cannot be detected if the AC is cycled ever day. We read the pros and cons about the benefits of duct cleaning and dont know if that would help or not? Any recommendations would be greatly appreciated.
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Penny







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Have you looked at the ac coil or pan or inside the ducts.
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Yup, clean the ducts. Sounds like a moisture build up problem that has dirt/dust trapped. The smell you are experiencing is most likely that musty smell of damp dirt.

sitting
replaced 10

first
bleach
plenum. The

clean.
smell is

and
smell
about
Any
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sitting
replaced 10

first
bleach
plenum. The

clean.
smell is

and
smell
about
Any
It is called DSS in the trade. Dirty Sock Syndrome.
First, its in your evap coil, not in your ducts, unless you have a kid that pissed into them, or threw his dirty towls into a duct. Second, unless you have true hard metal ducts, not insulated on the inside, you can clean your ducts, and then you can replace them.....since anything else will be destroyed... Your evap coil will need to probably be pulled, and foamed with the proper cleaner, flushed and re-installed....but we cant see it from here.
Look it up on Google..

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Our kids are all adults and long gone so it's not urine or dirty laundry. The ducts are hard metal without any coating in or out. However, it would require a professional to pull the coil as the two copper lines pass through holes in the plenum and will need to be unsoldered in order to remove the front furnace cover and get the coil out. And we are not experienced in the techniques required for that job. We can reach the coil through the humidifier opening in the plenum above the coil. The coil is an "A" frame and we could apply a cleaner and flush it in the furnace but that would certainly flood the basement. Guess our next step is to contact the installer. We suppose it would cost as much to clean the coil as it would to replace it?
We did a Google search and found that duct cleaning was not highly recommended. I'll do a Dirty Sock Syndrome search now. Thanks much for your replies.
Penny
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Penny wrote:

The humidifier is very likely the source of your odor.
hvacrmedic

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<snip>

The
require a

the
cover
for
Thanks hvacrmedic for your input. That was one of the first things we did. We disassembled the humidifier, tossed the evaporator unit and cleaned out the housing as best as possible. The heating/AC system is currently running with an empty humidifier housing and the water supply has been turned off. I apologize for not mentioning this earlier in my original post but I just forgot about it.
Penny
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