Joseph Meehan wrote:
Likely the coils or some parts of the system near them have a mold
problem and need to be cleaned.

So it was mold on coils. You were right! The fluid used to the cleaning
was all green afterwards.

I have no idea how difficult it may be to access that area,

It took a serviceman 15 minutes to get the device open.

but that
would be the best approach and do a though cleaning and disinfecting using
products suitable for A/C work.

Right! Thanks!