1. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPage 1 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: 1.Identify basic circuit diagrams 2.Identify a timer bar chart (timer cycle) 3.Apply your knowledge to reading circuit diagrams

2. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPage 1 Identifying basic circuit diagrams The Heating, Ventilation and Air Conditioning (HVAC) industry applies four basic rules when drawing circuit diagrams. BASIC RULES FOR READING ELECTRICAL SYMBOLS IN CIRCUIT DIAGRAMS— HVAC INDUSTRY STANDARDS 1.RELAYS and CONTACTORS are drawn in a de-energized condition. 2.SAFETY CONTROLS are drawn in their normal running position—closed. (There are some exceptions to this rule.) 3.OPERATING CONTROLS are drawn normally open. 4.TIMER MOTORS are drawn in the “ready to start” position or at “ time zero” on the bar cycle chart.

3. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPages 1 & 2 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. Figure 1. Connection Diagram Connection diagrams give component wiring instructions aid in identifying components

4. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPages 2 & 3 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 L 2. The hot wire is indicated by the notation L 1. Then each individual circuit is placed crosswise as the "rungs" of a ladder would be. Figure 2. Ladder Diagram

5. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPage 3 Figure 4. Simple Circuit Ladder 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.

6. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPage 4 Identifying a timer bar chart (timer cycle) Figure 4. Time 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.

7. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPage 5 Applying your knowledge to reading circuit diagrams Figure 5. Standing Pilot Furnace Parts Diagram

8. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPage 6 Figure 6. Standing Pilot Furnace Connection and Ladder Diagrams

9. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPage 9 Circuit Diagram Worksheet-Condensing Furnace Figure 7. Condensing Furnace Parts Diagram

10. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPage 12 Figure 9. Condensing Furnace Connection and Ladder Diagrams

11. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPage 15 Circuit Diagram Worksheet I-Heating/Cooling Packaged Unit Figure 10. Unit Heating Section Figure 11. Unit Side View Figure 13. Gas Valve & Burner

12. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPage 16 Figure 14. Heating/Cooling Packaged Unit Connection and Ladder Diagrams

13. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPage 18 Figure 15. Heating/Cooling Packaged Unit Connection and Ladder Diagrams

14. 7.4.2 Student Book © 2005 Propane Education & Research CouncilPages 21 & 22 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.