What you describe is common, almost considered normal when switching SEASONALLY but I can't think of a time I've heard of it when switching mode after a few days. Might not cure it but certainly can't hurt if you use Merv 10 or higher filters THAT FIT.

Dirty Sock Syndrome is merely a suggestive type smell as this is what the smell most often resembles, however due to how you live, how you operate the AC and Heat what type of system it is... heatpump with electric strip heat, gas furnace with AC or even straight AC with electric heat strips.

Florida is a heat pump market so I am going to assume you have a heat pump, with electric heat. That said, any system can exhibit smells doing the activity you are doing switching back and forth frequently from heat to cool and back to heat again.

UV lights and or the systems that contain them can cause irritative issues to the lungs if they produce ANY ozone what so ever. So it's important to check that. There are some that claim no ozone production but I'm on the side of not using gimmick gadgets that often do nothing more than part you from your money, not to mention the bulbs lose efficiency and most are required to replace bulbs annually even if the bulbs aren't burned out in that time.

Where the smell comes from could be mold growth, but more common and worse of a smell comes from bacteria. Trane was the company who coined the phrase Dirty Sock Syndrome, that being said ANY manufactured HVAC system can suffer from this type of thing... whether you wish to call it dirty sock syndrome or dirty vacuum bag syndrome is entirely up to you.

Why does this happen?

Bacteria is everywhere and newer HVAC systems have much bigger Evaporator Coils than years past, due to efficiency and changes mandated by law. DOE / EPA take your pick.

Condensate drainage... the bigger the Evap Coil, the more condensate it produces the more likely bacteria and or mold growth can occur. The coils are in some cases thicker, so UV lights are probably not going to do much as the bacteria can hide in plain sight even on a coil that doesn't look dirty to the naked eye.

Humidity: Another common problem to certain areas as with higher humidity it will only magnify this problem.

What you can do? Have the coil professionally cleaned. However, the coil is repeatedly washed free of any cleaning due to normal condensate that forms on the coil when run in AC mode.

Have the coil professionally treated? This is a service some have taken where the coil is removed shipped and then treated, shipped back and reinstalled. Probably not cheap and how long this may last is anyone's guess. The manufacturer of the coil may provide a treatment option by now?

The cheaper option?

You know how and why this is happening because you understand what you are doing that magnifies the problem... and that is switching back from heating and cooling and back to heating and back to cooling.

If you go to the doctor and you say hey when I do this (swinging my arm back and forth violently) it hurts. The doctor says: Quit doing that. ( I know this demonstration "choice of words here" sucks but there is no way on earth you misinterpret things. I'm not here to soothe your feelings I think you're old enough to handle it. Hopefully. )

If something is causing you grief limit that activity to a bare minimum.

The smell is often gone in time if you maintain the system in a single mode. I have a heat pump at my house (BOSCH Inverter) I occasionally get odd smells from it, smells more like car antifreeze to me because it smells "sweet" is about the best I can describe it usually when turning the heat pump on after a long period of mostly minor AC use. So just realize these smells are just nuisance smells in time they pass when you refrain from the activity that makes them.

Essentially the heat is killing the bacteria and that byproduct creates weird smells. In terms of filter use I use 1 inch pleated with 2 returns. The cheapest pleated filter I can find so nothing elaborate as the more restrictive the filter doesn't add up to anything good in my opinion.

I also don't have any gimmick gadgets like UV bulbs or air scrubers etc, as I said they loose efficiency and require bulb replacement after about a year of use whether they burn out or not. You decide what you want to spend money on.

For me the smell subsides usually within a few hours of operating the system in Heat Mode and then refraining from constantly switching back and forth from heat to cool and back. Which can be difficult living in a warm and often very humid climate.

I service the Katy, Texas area.

Hi, connerhm,

I'm sorry for your experience. I'm betting others in your area have had similar experience. To determine the root cause of your air quality problem--assuming your system and duct work have been thoroughly inspected visually-- I think you'll need air sampling and analysis to be performed. I suggest you contact your state's health department for assistance:

https://www.floridahealth.gov/community-environmental-public-health/environmental-public-health/air-quality/

I do not service the Katy, TX area, but I had my car serviced there many years ago.

You guys are awesome! I can't thank you enough! Austin Air Companie, that is more information than I've gotten in the past 2 years. Best explanation and very helpful. Thank you for taking so much time to explain it. Klem1, I agree with you about the filter. Great suggestion. Charles Ross Homes, thank you; that's an avenue I hadn't thought of!

You guys are awesome! I can't thank you enough! Austin Air Companie, that is more information than I've gotten in the past 2 years. Best explanation and very helpful. Thank you for taking so much time to explain it.

connerhm, You're welcome. I've been at the HVAC career a long time over 30 years and HVAC smells are a complicated issue to the point in which certain manufacturers conducted tests and determined that much of this problem was the fault of the "operator of the system" as when those folks moved, the tests continued and it was determined to be in how the system was being operated.

On occasion I've come into contact with some who exhibit the smells just running in the AC mode without switching back and forth to heat, but the problem only appeared in the shoulder seasons typically in the period of Oct thru Dec -- only warm climates will have that kind of opportunity as most markets by that time are using heat as opposed to AC.

So the suggestion if that happens is to lower the thermostat setting typically a few degrees to force the unit to run longer AC cycles as during that period it's still warm, just not as warm and the longer run times will drop humidity levels to a more appropriate level as that often times has something to do with these kinds of smells.

Many like to approach these kinds of complaints as an avenue to push sales rather than to really fix something or even explain it fully. I'm more in the camp of explaining it so you can either take the appropriate action to clean it (which will temporarily fix it) or take a more user friendly approach to modify the behavior that is likely producing the problem.

Even after 30 years I still run into people such as yourself who have little to no knowledge of why the problem even happens to begin with, which seems kind of crazy to me.