The fresh air (series) air conditioning unit is suitable for various occasions that use fresh air systems, and can also be used for fresh air systems that use fan coil units. The fresh air (series) air conditioning unit itself does not come with a cold or heat source. When in use, the outdoor fresh air is filtered through a coarse filter, cooled (or heated) by a heat exchanger, and then sent into each room through pipelines. The unit has the advantages of compact structure, low noise, elegant appearance, smooth operation, and easy disassembly and assembly, and is widely used in various places such as hotels, shopping malls, industrial and mining enterprises, hospitals, office buildings, etc.