A HVAC control system diagram is a visual representation of the components and functions of a HVAC system. It is used to help identify and troubleshoot problems in the system, as well as to design and install new systems. The diagram typically includes the components of the system, such as the thermostat, air handler, ductwork, and other components. It also shows the relationship between these components and how they interact with each other. Additionally, the diagram will show the wiring and other connections between the components, such as the power source and the air handler. The diagram is also used to show the control logic of the system, which is the sequence of operations that the system will follow in order to maintain the desired temperature and humidity levels. By using a HVAC control system diagram, technicians and engineers can quickly identify and diagnose problems in the system, as well as design and install new systems.