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7.4.2. Reading Electrical Control Circuit Diagrams. In the course of repairing a gas appliance, technicians must routinely refer to electrical circuit diagrams. In this module, you will learn to:. Identify basic circuit diagrams Identify a timer bar chart (timer cycle)
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7.4.2 Reading Electrical Control Circuit Diagrams In the course of repairing a gas appliance, technicians must routinely refer to electrical circuit diagrams. In this module, you will learn to: • Identify basic circuit diagrams • Identify a timer bar chart (timer cycle) • Apply your knowledge to reading circuit diagrams
Identifying basic circuit diagrams The Heating, Ventilation and Air Conditioning (HVAC) industry applies four basic rules when drawing circuit diagrams.
Figure 1. Connection Diagram Connecting or Component Diagram Connection diagrams, sometimes called component location diagrams, use symbols for various parts of the control system. The parts of the control system are located on a piece of paper in much the same relative position as they are used in the equipment. Connection diagrams • give component wiring instructions • aid in identifying components
Ladder Diagram Ladder diagrams use symbols for the component parts. Wires connect the symbols to their control units as simply as possible. Wiring is arranged as follows: The leads from the power source are drawn vertically on the paper much as the "side rails" of a ladder are located. The neutral wire in a ladder diagram is indicated by the notation L2. The hot wire is indicated by the notation L1. Then each individual circuit is placed crosswise as the "rungs" of a ladder would be. Figure 2. Ladder Diagram
Unlike the component diagram, the ladder diagram does not show the actual location of components. Ladder diagrams are useful in determining sequence of operation and how loads are activated in a circuit. Notice that in HVAC ladder diagrams, the step down transformer is the central component and divider between high voltage load circuits and lower voltage control circuits. Ladder diagrams graphically illustrate the requirements for safe current flow. Figure 4. Simple Circuit Ladder
Identifying a timer bar chart (timer cycle) Time bar charts are true sequence-of-operation control diagrams. Also caller timer cycle charts, these diagrams are commonly used to communicate sequence of operations for clothes washers, dryers and dishwasher. Unlike circuit diagrams which provide wiring and wiring connection information, time bar charts give technicians the means to troubleshoot a series of equipment systems that are controlled through a timed sequence. Figure 4. Time Bar Chart (Timer Cycle)
Applying your knowledge to reading circuit diagrams Figure 5. Standing Pilot Furnace Parts Diagram
Figure 6. Standing Pilot Furnace Connection and Ladder Diagrams
Circuit Diagram Worksheet-Condensing Furnace Figure 7. Condensing Furnace Parts Diagram
Circuit Diagram Worksheet I-Heating/Cooling Packaged Unit Figure 10. Unit Heating Section Figure 13. Gas Valve & Burner Figure 11. Unit Side View
Figure 14. Heating/Cooling Packaged Unit Connection and Ladder Diagrams
Figure 15. Heating/Cooling Packaged Unit Connection and Ladder Diagrams
Time to See If You Got the Key Points of This Module… • Complete the Review on page 21. • See if you are ready for the Certification Exam by checking off the performance criteria on page 22.
