Steps we take to resolve odor related issues.
First Off... bear in mind
Since not all odor problems are the same
The steps I use are general guidelines
Since the steps can become more and more expensive...
sometimes I go so far and stop to see if what I did fixed it. i.e. allow a chemical to take effect
I'm not making this out to be a step by step here's how you do it homeowner thing.... I fully recommend an HVAC tech to do this stuff. Think of this as a prep of what to expect if I were to come out and do it. Other techs may take a different approach which may be better (or worse), so if your hvac comp does something a bit different, that don't mean they are flat out wrong... it just means they are different.
With that out of the way....
Determine SOURCE. HVAC System or HOUSE (sometimes the 'source' is in the attic, crawlspace, wall, etc. the duct system can pulls in the smell, stirs it up, and alot more possibilities. i.e. Cat getting under house and using it as a litter box, sewer vent terminating in attic, mice getting in ductwork (their droppings make good breeding ground for molds/mildews)
If it is the HVAC System.
Check operation and performance of equipment (This often
leads to finding other problems that need to be addressed not related to the odor. i.e. I've come across lots of dirty outside coils.
Verify correct airflow through equipment.
Inspect duct system and evap coil.
I have a special petri dish where I collect air samples and store the petri dish for a week or two and see what starts to grow in it. We have a chart that gives an idea of what we're looking at and gives us an idea if we need to have the dish sent off to a lab for further evaluation or wether its nothing to be concerned about.
We can just send the dish off if the homeowner wants us to.
Some people really just want to know.
By the way... this is the most Biblical path.
Leviticus 14:45 A house desecrated by mildew, mold, or fungus would be a defiled place to live in, so drastic measures had to be taken.
Leviticus 13:47-50 If any clothing is contaminated with mildew---any woolen or linen clothing, any woven or knitted material of linen or wool, any leather or anything made of leather---if the contamination in the clothing or leather, or woven or knitted material, or any leather article, is greenish or reddish, it is a spreading mildew and must be shown to the priest. The priest is to examine the mildew and isolate the affected article for seven days…
Leviticus 11:47 You must distinguish between the unclean and the clean…
After collecting the sample, I spray evap coil with a chemical treatment (i.e. possible dirty sock syndrome, or unseen growth in the coil. The chemical we use acts as an enzyme that disolves the offending odor bacteria)
I normally stop here and give the chemical time to do its job.
I leave the job at the time and allow the chemical to do its job. If the petri test does not show up anything to be concerned about AND the homeowner indicates that the odor is gone, then we call it finished.
If the smell persists...
I check the system closer... including cutting in inspection holes to view the inside of the duct better.
I check everything over with a fine tooth comb.
Sometimes, even then I don't 'see' anything.
Keep in mind, smells are microscopic, that don't mean you can see them or the source with your bare eyes.
If nothing comes up.... I 'fog' the duct with a chemical
I also fog the environment the duct is in (attic or crawlspace)
(We dont' charge a return trip we figure it as if the tech did not leave the first time... we do charge for the extra work though... keep in mind, one of the reasons I stop between some steps in for the bill not to get super expensive all at once.... work on it till the prob is fixed... dont' pull out all the canons at once)
Anyways.... after fogging the system, I give it a couple weeks to see if that kills the odor/source.
If the odor persists....
We have a 5 step cleaning process. (totaline)
If its a split system, we remove the evap coil and take it outside.
Spray it with a chemical coil cleaner, wash it off, treat it with two other chemicals, put it back together, put a pan strip in, and it comes with an odor absorbing stuff in a little container that looks like what you'd get potato chip dip out of.
If we end up with a major problem...
we install a UV Light and 5" pleated filter
I can't think of any job that I couldn't find the source and correct the problem.