Recently had a Dometic 15000 Btu low profile AC installed replacing a 13000. After unit runs for a period of time, from one to four hours, the fan starts cycling. By cycling, it changes speed from high to low, low to high or sometimes just off and on...
Pulled mine several times and never have gotten soot. If you let you unit idle quite a bit, you will probably get soot. I try to keep mine loaded as much as possible when I run it.
Other people have had this problem including myself. The easiest way that I found that cured mine was to buy the venturi directional vent and install one on each tank (grey and black)vent.
Could we get a picture. Mine has a trim above it that is held in place by screws. Once that is removed it is easy to get to the screws that hold the unit in place.
