I have a vacation home in Mexico (Cabo) built in 2003. It has individual Trane Mini Splits for the bedrooms. They are only occasionally used, but the one in the main bedroom (most use) will develop a foul odor after a week or so of being on in the evenings. I have read about the “dirty sock” smell but this is more like a dirty urinal than a sock. At it peak it will drive you out of the room. In fact I was so convinced it was sewer odor that I several years of looking elsewhere I insisted that the A/C must be hooked up to the sewer system. They looked, and it was! First they put in a trap, but that did not do it. Then I had them rip out a wall, repair the sewer vent and reroute the drip line. Now it drains to the outside of the house, the drain is working, but smell has come back. Big loss in Gringo credibility.
The air handler is concealed in the ceiling of the closet and has about 10 feet of duct (across the bathroom) to the bedroom. Outside unit is 3 ton, 2TTB3036A1. The air handler model is MCD536D1. If there is any heating capability I have not found it. I think the system is cool only. Access to the air handler is difficult (one side only). The pan sticks out an inch or so longer than the unit on each end so you can stick you finger up there and feel the drain hole. (I am not sure how they keep fan air from exiting though the pan, but I have not noticed it.....maybe there is more stuff in there to expel the moisture than I realize?). Putting pool chlorine in the ends of the pan helps sometimes, but not always and the smell comes back fairly quickly in any case. Water going into the drain does not seem smelly, but it may be getting the chlorine. Unit has four fans (driven by two motors) on the side where there is access. Unit is “almost” level (tilt is a little wrong), but I plan to tilt it a little towards the drain to be sure. The blocked drain on the other end of the pan does not seem to collect water.
I am looking for any suggestions, ideas or speculation that might be of help. I don't have a lot of faith in the skill or experience of the local Trane folks, although I think they will do most things I suggest if they make sense. Ripping the whole unit out for cleaning or inspection will mean taking down some wall board in the closet ceiling. Since the problem started within the first year or so, and the unit is rarely used and the climate is dry most of the year I am not sure that will get it done.
Again, any suggestions are appreciated.