I have a horrible fishy smell coming from the downstairs vent. I have two air-conditioning units. One that runs the upstairs and one that runs the downstairs. The units themselves are outside. I have had someone come and take a look at the units. The gentlemen took a look in the attic and stated that everything was fine and that he could not tell me what the smell was. The smell is not a constant smell, nor does it only happen when the air is on Since it is not a constant smell I really haven't had it looked at until this summer. It seems that it got worse this summer. I am faithful about changing the filter's and I don't see anything around the vent that would indicate that the vents are dirty. Please help with this embarrassing smell.

The only thing you could have done was to have the indoor A/C coils cleaned. Many times this can be a source of smell complaints.