An air-handling unit in its most general definition is just a metal box that contains a fan, filters, a heating element, and a cooling element, and an outside air damper. It can be used with a variety of delivery systems, such as a variable air volume (VAV) system, a constant volume (CAV) sytem, or a dedicated outdoor air (DOAS) system. To get any more specific than that, you need to define what your source of heating and cooling is.

An air-cooled condensing unit is just describing the heat rejection method of a cooling source. Heat rejection methods include air-source, water-source, and ground-source. A DX cooling unit would have an air-cooled condensing unit, as would an air-source heat pump.

It's important to both define how you are delivering air, whether it is a multi-zone or single-zone system, and what the heating and cooling source is. In practice, AHU often indicates a multi-zone system (instead of a packaged single zone unit).

If you want to create a quick system that uses DX for cooling, you can click the plus sign the HVAC Systems section of OS and select a template system. There are several options with air-cooled DX or heat pumps.