The Air Handling Unit (AHU) is the heart of the central air conditioning system. It collects outside and indoor air, removes dust and other particles from the collected air, regulates temperature and humidity, and delivers comfortable, refreshing air conditioning to the room. Air handlers are designed to move air. That's all. It does not heat or cool, it moves the air. Air conditioners, on the other hand, simply cool the air by taking heat from the outside air.