What is Dirty Sock Syndrome: It’s the smell coming from your Air Conditioning unit caused from Mold, Mildew, and the decay from Microorganisms. These things build up on your indoor evaporator coil, primary drain pan, plenum and even ductwork.

Usually during the Summer these things get washed off the coil due to just the natural cycle of air conditioning humidity removal and this washes these debris from the coil. During the heating season the microorganisms basically die and stick to the evaporator coil. When the AC gets cycled on during mild weather the system doesn’t run as long as it does during the Summer and the indoor Humidity is lower so there’s not much water being washed over the coil to wash these decaying organisms’ debris from the coil, so the result is that musty stinky smell you get coming from your air conditioning system. 

After being in the HVAC industry for 35 years now this always seems to take place December thru March; these are the times where everyone seems to be switching between Heating and Cooling. Sometimes the evaporator coil can just be cleaned with a good anti-microbial coil cleaner to relieve these issues. Depending on the severity the coil may need to be pulled out of the system to be cleaned, sterilize the duct system, add better filtration, and even install some type of UV lighting system to kill and sterilize these partials in the air stream. 

Need to have an HVAC licensed professional inspect the system to determine the best plan of action and solution to resolve this issue. It best to have the system sterilized and determine what is causing the problem, if the problem isn’t addressed and corrected the dirty sock smell will return within 2-4 weeks.