A HVAC fan coil unit is a device used in heating, ventilation, and air conditioning (HVAC) systems to regulate the temperature of a room or building. It consists of a fan, a coil, and a filter. The fan draws air into the unit, where it passes through the filter to remove dust and other contaminants. The air then passes through the coil, which is heated or cooled depending on the desired temperature. The air is then blown out of the unit, either directly into the room or into a duct system, depending on the system setup. The fan coil unit is an important part of an HVAC system, as it helps to regulate the temperature of the room or building, as well as filter out dust and other contaminants. It is important to maintain and service the fan coil unit regularly to ensure it is functioning properly and providing the desired results.