HVAC system smells like decay, death or diapers


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Old 05-07-16, 12:47 PM
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HVAC system smells like decay, death or diapers

I've been trying to debug a smell that I thought was a dead mouse. It has been going on for about 3 months whenever the fan blows. (it's spring, so we haven't had to use it much over those 3 months)

I borrowed a borescope from the local airport, and took apart the HVAC system today, looked in vents, etc. I can not find a rat. The house was built in 2007 (HVAC was new at the time) so it's pretty clean in the ducts.

Notables:
  • Smell is stronger from vents near the trunk (vertical).
  • It smells regardless of if AC or Heat is on. Just the fan being on produces the smell)
  • Filters have been changed 2 months ago and are clean
  • It does NOT smell anywhere if the system is off. Even in the vents where it's typically strongest, if the system has been off, the stink isn't there.


Descriptions of smell
  • To me, it smells like dead mouse
  • To my wife, it smells like dead mouse or really old dirty diapers
  • To the people renting the basement, it smells like decay.


I'm not technically a HVAC expert. But, I did watch a few Chip and Joanna shows, so I'm pretty much one. (kidding)

As far as HVAC inspections go, I ran the borescope down the vents and into the main horizontal trunk, opened the furnace and looked top/bottom of the V thing, looked up the vertical return trunk, and inspected the aux heat coils from the top. I also inspected inside the blower (without taking it apart) just looking through the fins with the borescope towards the bottom. Nothing weird seemed there.

What do you think?


[Note: The system is a typical Missouri electric heat pump with aux heating.]
 
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Old 05-07-16, 12:58 PM
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That only leaves old water in the condensate pan directly under the evaporator coil.
 
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Old 05-07-16, 01:22 PM
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Did you just inspect the heating supply vent and trunk lines or did you also do all the air return vents and trunks (you mentioned the return trunk next to the furnace). Sometime returns are just panned over joist or stud cavities and it's easier for critters to get into those than the all metal supply lines.....

3 months is a long time for (a small) dead critter smell to remain strong, so Pete may have put his finger on it.
 
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Old 05-07-16, 01:57 PM
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Update

After running the fan for about 45 minutes, I shut it off and smelled things. The smell was particularly strong in the furnace area. I couldn't pinpoint where the smell was coming from in particular.

I noticed the blower *motor* was extremely dusty, and I used the borescope to look inside that motor itself. Other than a lot of dust, I didn't notice anything abnormal.

CarbideTipped - I only looked up one of the returns in the ceiling (connecting master bedroom return to vertical return) and then realized that due to the length of the return and bends, it was going to be a hassle seeing far enough with this borescope, so I gave up on that route and can return to it if that seems likely.

PJMax - I didn't check this (will research how). This is particularly interesting. Last summer, we had an issue where it wasn't cooling properly, and the HVAC guy came out and pulled out the filter which was 100% soaked. He said something about the drain pan but other than replace the filter, nothing was done.

Probably unrelated - It seems like we have a refrigerant leak, as the past two years the HVAC guys have had to add some (the second year was a different guy, and he wanted to wait until this season to check it again in order to see what the rate of loss is) Also, the HVAC guys have made it clear that the system is underpowered for our house now that we've finished the full basement and it's being used for that as well (though it was ducted before we finished it) In case either of these things are related in any way, I'm throwing them out...hopefully they are not red herrings.



A few minutes ago, I sprayed Nu-Calgon 417175 Evap Foam on the fins (v-shaped thing)
I'll see if that happens to do the trick, and will research the drain pan check in the meantime.

Thanks for your help.
 
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Old 05-07-16, 02:33 PM
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I had one stuck on the inside of my squirrel cage fan on wifeys Jeep Cherokee. I finally had to take it all apart and get him/her out as the smell of death was horrible in a closed up cabin.
 
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Old 05-07-16, 03:56 PM
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There is usually.... but not always.... a side panel that will come off and allow you access to the evap coil and pan. The pan will be located at the point where the drain line exits the unit.

Loss of refrigerant won't cause an odor.

You sprayed which fins ? The evaporator inside the air handler ?
 
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Old 05-07-16, 04:28 PM
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I sprayed the fins on the evaporator coil. I see pictures of a side panel that comes off. I'll give that a try and do some inspections there.

And, I'm a moron. I thought I had looked under the evap coils, but apparently I was probably just looking at the bottom of the drain pan. I didn't realize the side came off, so I just stuck the borescope underneath. I didn't know what to expect, so when I saw only metal but no rats, I thought that must be good. So, I will definitely need to remove that panel to make sure nothing weird is in there, as that part has not been checked at all.
 
 

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