There are three different types of electrical diagrams used in HVAC systems: wiring schematics, line diagrams and installation diagrams. Each one has its specific use in relation to the installation or maintenance of an HVAC system, but the most commonly used diagrams are wiring schematics.
A wiring schematic, sometimes referred to as a ladder diagram, shows the flow of current in the HVAC system. The schematic features several different types of symbols that stand for certain components in the system, as well as different colored lines. Wiring schematics are commonly used in finding damaged or frayed wires that are causing electrical problems.
A line diagram, also referred to as a wiring diagram, uses more detailed illustrations. There is more focus put into what each component looks like, as well as the function of the components themselves. These diagrams differ from a wiring schematic as they are more focused on the components instead of the current flow.
An installation diagram is used while setting up an HVAC system into a home. These diagrams typically show where each connector on the terminal board is located and how to route them. These diagrams rarely feature more detailed information, such as the internal wiring of an HVAC systems terminal box.