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Basic Electrical
For the
Heating, Ventilation, and Air Conditioning Technician
Written By:
Christopher Molnar
Copyright © – Our World Services, LLC – 2006, 2007, 2008, 2009, 2025
All Rights Reserved
Permission to freely use and distribute current version granted to:
Porter and Chester Institute, Inc.
TABLE OF CONTENTS
Introduction – Welcome to electronics……………………………………………………… 5
Why this manual is needed?………………………………………………………………………………….. 5
How this manual is organized?………………………………………………………………………………. 5
What supplies and equipment will you need?……………………………………………………………. 5
What is electricity?……………………………………………………………………………………….. 7
Introduction……………………………………………………………………………………………………… 7
Alternating current…………………………………………………………………………………………… 9
Direct current…………………………………………………………………………………………………… 9
Line voltage…………………………………………………………………………………………………….. 10
Control Voltage………………………………………………………………………………………………. 10
Resistance……………………………………………………………………………………………………….. 10
Introduce first 5 symbols…………………………………………………………………………………… 10
Switch…………………………………………………………………………………………………………… 11
Source………………………………………………………………………………………………………….. 11
Light Bulb……………………………………………………………………………………………………… 11
Transformer……………………………………………………………………………………………………. 11
Fuse…………………………………………………………………………………………………………….. 11
Safety…………………………………………………………………………………………………………….. 12
Glossary of Terms…………………………………………………………………………………………….. 13
Build a circuit………………………………………………………………………………………………….. 14
First shop project……………………………………………………………………………………………… 14
Ohms Law…………………………………………………………………………………………………………. 16
Laws of Electricity…………………………………………………………………………………………… 16
How to use a meter………………………………………………………………………………………… 18
Introduction to meters………………………………………………………………………………………. 18
Types of meters…………………………………………………………………………………………………. 18
Open Circuits……………………………………………………………………………………………………. 20
Complete Circuits……………………………………………………………………………………………… 20
Measuring Voltage…………………………………………………………………………………………… 21
Measuring Current……………………………………………………………………………………………. 21
Measuring Resistance………………………………………………………………………………………… 23
The “Hop-scotch” method of tracing circuits…………………………………………………………. 24
Glossary of Terms…………………………………………………………………………………………….. 25
Review of the basic rules of electricity………………………………………………………………… 25
Shop Project – Trace the circuit you just built……………………………………………………….. 25
Source, Switch, Path, and Load…………………………………………………………………….. 28
Introduction……………………………………………………………………………………………………. 28
Series Circuits………………………………………………………………………………………………….. 28
Loads in series………………………………………………………………………………………………….. 29
Parallel Circuits……………………………………………………………………………………………… 30
Glossary of Key Terms………………………………………………………………………………………. 32
Shop Project – Build a Series Circuit…………………………………………………………………….. 32
Shop Project – Build a Parallel Circuit………………………………………………………………… 35
The Relay………………………………………………………………………………………………………… 38
Introduction……………………………………………………………………………………………………. 38
Contacts…………………………………………………………………………………………………………. 38
Normally Open………………………………………………………………………………………………… 38
Normally Closed………………………………………………………………………………………………. 38
The Relay Coil………………………………………………………………………………………………….. 38
Coils Ratings…………………………………………………………………………………………………… 39
Contact Ratings……………………………………………………………………………………………….. 39
Contact Configuration……………………………………………………………………………………….. 39
Operation………………………………………………………………………………………………………. 39
The Symbols…………………………………………………………………………………………………….. 40
Sequence of Operation……………………………………………………………………………………….. 41
Glossary of Key Terms………………………………………………………………………………………. 42
Line Voltage Relay Shop Project…………………………………………………………………………. 42
The Transformer……………………………………………………………………………………………. 47
Introduction……………………………………………………………………………………………………. 47
Description and Basic Theory of a Transformer……………………………………………………… 47
Review of Control and Line Voltage…………………………………………………………………….. 48
Glossary of key terms……………………………………………………………………………………….. 48
Shop Project – Build a circuit with a transformer…………………………………………………… 49
Thermostats…………………………………………………………………………………………………… 53
Types of thermostats…………………………………………………………………………………………. 53
The Heating Thermostat……………………………………………………………………………………… 53
The Cooling Thermostat……………………………………………………………………………………… 54
Thermostat Sensing Elements……………………………………………………………………………… 55
Bi-Metal Sensing Elements………………………………………………………………………………….. 55
Remote bulb sensing element………………………………………………………………………………… 55
Solid State Sensing Element…………………………………………………………………………………. 57
Thermostat Wiring……………………………………………………………………………………………. 57
Glossary of Terms…………………………………………………………………………………………….. 58
Troubleshooting Section…………………………………………………………………………….. 59
Problem: I do not think my meter is working properly………………………………………………. 59
Problem: I think I just tripped the circuit breaker as I have no power to my test board…… 59
Problem: I just got a shock from the circuit I am working on……………………………………… 59
Appendix A – Electrical Schematic Symbols………………………………………………. 61
Works Cited…………………………………………………………………………………………………….. 63
Illustrations
Figure 1 – Atomic Structure of an Atom (Porter and Chester Institute) 7
Figure 2ß – 120 Volt Alternating Current (Whitman, Johnson, Tomczyk 60) 9
Figure 3 – Basic Schematic Diagram.. 12
Figure 4 – Shop Wiring Diagram Basic Circuit 15
Figure 5 – Analog Meter (Smith 60) 18
Figure 6 – Digital Meter (Smith 60) 18
Figure 7 – Checking voltage across a light bulb. 20
Figure 8 – Ammeter with clamp around circuit 21
Figure 9 – Ammeter with leads connected in series to circuit 21
Figure 10 – Circuit from figure 4 with points marked. 25
Figure 11 – Series Circuit two loads in series 27
Figure 12 – Series Circuit two switches in series with load. 28
Figure 13 – Series circuit with two light bulbs. 28
Figure 14 – Series Circuit with three switches and one load. 29
Figure 15 – Simple Parallel Circuit 29
Figure 16 – Parallel Circuit with switched loads. 30
Figure 17 – A Series Circuit with one switch and two bulbs 32
Figure 18 – Parallel Circuit with one switch and two bulbs. 35
Figure 19 – Relay contacts and coil on line voltage. 39
Figure 20 – MARS relay (Courtesy MARS, Inc.) 41
Figure 21 – MARS relay wiring diagram (Courtesy MARS, Inc.) 41
Figure 22 – Line voltage relay wiring circuit 42
Figure 23 – Transformer step-down circuit 45
Figure 24 – Transformer and relay shop circuit 47
Figure 25 – The heating thermostat 51
Figure 26 – The cooling thermostat 51
Figure 27 – Bi-metal sensing element (NATE C134) 52
Figure 28 – Remote bulb thermostat 53
Figure 29 – Remote bulb thermostat from window air conditioner 53
Figure 30 – Basic Schematic Symbols (Porter and Chester Institute) 57