Both "connecting" and "connection" can be used when referring to air systems, but their usage depends on the context.
Connecting: "Connecting" is a verb that implies the action of joining or linking different components or parts of an air system. For example, you can say, "I am connecting the air conditioner to the ventilation ducts." Here, "connecting" emphasizes the ongoing process of establishing a physical or functional link between different elements of the air system.
Connection: "Connection" is a noun that refers to the point or state of being joined or linked. It signifies the established relationship or link between different parts of an air system. For instance, you can say, "Ensure that the connection between the air handler and the ductwork is secure." In this case, "connection" emphasizes the established state of linkage or the point where the components are joined.
So, to summarize, "connecting" is used to describe the action of joining or linking components, while "connection" is used to describe the established link or relationship between the components of an air system.