I have a strange problem and wondering if anyone has any insight. A few weeks ago, our four year old Trane went out due to a bad capacitor. It was down for two days over the weekend. (in the middle of July in Florida). It was fixed and worked fine with no issues. About a week later, I went out of town and left it set on 82 as I normally do when traveling. I lowered the temperature on my way home as usual. Once I was home, I noticed that evening there was a strange musky-like smell (or maybe vinegar like smell) in the living room. I could not find the source of it. The next day, it was gone. That evening, the smell returned.

I spent this week trying to pinpoint the source, and realized the smell only occurs after the sun goes down and seems to stick around until the next morning and slowly fades as the day heats up. I finally tracked this down to coming out of one vent in the house. I can faintly smell it from one other one, but none of the others smell. I've checked the unit itself and the filter and the smell is not present. I went into the attic to check the ducts and everything appears in-tact and nothing out of order.

Has anyone ever experienced this? Does anyone have any ideas on what it could be or what I could try checking? I called our local A/C company that does our maintenance and repairs and they're going to come late this week if it is still happening, but it would be nice to try to track this down and solve it ahead of time.