Heating and Air Conditioning equipment is the victim of and not the source of "Dirty Socks Syndrome".
This phenomenon most generally occurs on replacement systems where pre-existing equipment has been replaced. Either the increased airflow of the new equipment or the disturbing of the old existing ductwork has dislodged the micro-organism.
In the late 1980's and early 1990's IAQ became a nationally recognized issue, "Dirty Socks Syndrome" is an unofficial name that was given by contractors to a foul odor that smelled somewhat like dirty gym socks. The reports have been more predominate on Heat Pump units and seemed to occur more during the Spring and Fall seasons when the units would be used in the heating mode during the night and cooling during the day.
Generally, an annual thorough cleaning of the coil surfaces and the drain pan will help to minimize the odor. Trane Parts does offer a coil pre-cleaner Trane Part # (EVP027401) and an anti-foulant treatment Trane Part # (CTG027301) that can be used to clean and treat the coil.
See the attached article describing the dirty sock syndrome for more details.
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.