RSES Journal Winter 2025, RETA-RSES

Quite often, an HVACR equipment problem turns out to be an electrical problem. Electrical schematics serve as maps to assist HVACR technicians trying to solve any number of HVACR system failures. CHARTING A SERVICE PATH WITH ELECTRICAL SCHEMATICS

H VACR equipment problems are often electrical in nature, so a clear understanding of how to read wiring diagrams can help a technician find the source of the problem, by comparing the HVACR unit’s wiring against the manufacturer’s wiring diagram. A wiring diagram may appear complex when viewed as a whole, but it can be simplified by breaking it down into smaller parts. Key to the technician’s understanding is that there are always five basic components to any schematic: • a power supply; • a path for the power; • a load or component that interrupts the power to the load; and • a legend or key that explains the meaning of the symbols and abbreviations used in the schematic. Types of Wiring Diagrams Three types of wiring diagrams are used in the HVACR industry today. The most common is the ladder diagram, so called because it looks like the symbols used to represent the components in the system are placed on the rungs of a ladder. In this review, ladder diagrams will be referred to as “schematic” diagrams or simply “schematics.” Figure 3-1 shows a schematic of a packaged air conditioner. The symbols stand for various components in the circuit, and the lines represent wires. A line diagram usually includes diagrams that more closely resemble the components themselves rather than symbols. Figure 3-2 shows a typical line diagram. Compare it with Figure 3-1 to notice how the way motors, switches and transformers are represented in each type of diagram.

The installation diagram is used primarily by the installing contractor. It normally shows only the terminal board connections, and will rarely include any internal wiring of the unit. Figure 3-3 is a typical installation diagram for a residential cooling system.

Figure 3-1 Typical schematic diagram.

18 RSES Journal WINTER 2025

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