BASIC ELECTRICAL FOR THE HVAC TECHNICIAN
Introduction
Welcome to Basic Electrical for the Heating,
Ventilation and Air Conditioning Technician.
Electrical knowledge is one of the most important skills
you will develop as an HVAC/R technician. You can become
very good at installation and mechanical service work,
but sooner or later you still have to understand what the
electrical circuit is doing.
Why This Manual Exists
This manual was originally written as part of a formal
HVAC/R training program. The goal was not to turn HVAC
students into electricians. The goal was to give them
enough electrical understanding to safely diagnose,
repair and service the electrical systems they would
encounter in the trade.
HVAC/R equipment depends heavily on electrical controls.
Motors, compressors, relays, contactors, transformers,
thermostats and safety devices all depend on electrical
circuits operating correctly.
If you do not understand those circuits, troubleshooting
becomes guessing.
Having this manual in your hands will do no good unless
you absorb the skills it contains.
Read the material, work through the examples, build the
circuits when you have the opportunity, use your meter,
and ask questions when something does not make sense.
How to Use This Material
Electrical troubleshooting is a skill. You develop it
by understanding the principles and then applying them.
Understand It
Do not simply memorize that a meter should read a
certain number.
Understand why you expect that reading and what it
means when the reading is different.
Practice It
Electrical theory makes much more sense when you
connect it to an actual circuit.
Build circuits, trace them, measure them and compare
what happens to what you expected to happen.
Ask Questions
If you do not understand why a circuit behaves the
way it does, stop and work through it again.
Asking why is how you move from memorizing procedures
to understanding electrical systems.
Do the Work Yourself
Watching someone else wire a circuit or use a meter
is not the same as doing it yourself.
The more hands-on experience you get, the more useful
the theory becomes.
How the Original Course Was Organized
The original classroom version of this material was
organized into eight sections and taught as part of
a structured HVAC/R program.
Classes combined classroom instruction with hands-on
shop work. Students would normally spend part of the
session learning the electrical theory and the rest
of the session building and testing circuits.
Shop projects were checked by an instructor before
the circuit was energized.
If you are using this material independently, you will
not have that same classroom structure, but the learning
sequence still matters. Work through the lessons in order
whenever possible.
What You Will Learn
The course begins with the basic electrical principles
and gradually moves toward the circuits and controls
used in HVAC/R equipment.
Electrical Fundamentals
Electricity, voltage, current, resistance,
alternating current, direct current and Ohm’s Law.
Circuits
Source, switch, path and load, along with series and parallel circuits.
Meters
Measuring voltage, current and resistance and using
those measurements to understand circuit operation.
HVAC Controls
Relays, transformers, thermostats, switches,
control voltage and sequence of operation.
Schematics
Reading circuit drawings and recognizing the symbols
used to represent electrical components.
Troubleshooting
Applying the theory, the schematic and your meter
to find where a circuit stops operating correctly.
Tools & Equipment
The original course used basic electrical hand tools,
a meter and a training board for the shop projects.
Digital Multimeter
Your meter will become one of the most important
diagnostic tools you use in HVAC/R service work.
Basic Hand Tools
Screwdrivers, wire cutters, wire strippers,
pliers and other basic electrical hand tools
are used throughout the shop projects.
The Electrical Training Board
The original course used a training board so students
could build, power and troubleshoot simple electrical
circuits in a controlled environment.
Depending on the exercise, the board could include
switches, light bulbs or other loads, relays,
transformers, thermostats and protective devices.
The purpose of the board was not simply to make a circuit
work. The important part was learning how each component
affected the circuit and how to use a meter to prove
what was happening.
Build it. Measure it. Understand why it works.
Safety Comes First
Electrical work can injure or kill you. It can also
damage equipment or create a fire hazard.
During the original classroom course, students were
required to begin shop assignments with the circuit
unplugged and de-energized. The instructor inspected
the circuit before it was powered.
If you are studying independently, do not treat the
absence of an instructor as permission to experiment
with energized circuits.
Know whether the power is on or off before you touch
the circuit.
When resistance or continuity measurements are required,
de-energize the circuit first.
Learn the Vocabulary
Every trade has its own language.
Electrical terminology matters because technicians need
to communicate clearly with other technicians, read
schematics and service information, and understand
exactly what a circuit is doing.
Terms such as voltage,
current, resistance,
source, load,
path and switch
will appear throughout this manual.
Do not worry if every term does not make sense yet.
They will become more familiar as you use them.
A Word Before You Begin
Do not rush through this material simply to finish it.
When something does not make sense, go back and work
through it again.
The goal is not to memorize enough information to pass
a test. The goal is to understand electrical systems
well enough that you can apply the information when
equipment is sitting in front of you and not working.
As you move through the course, keep asking yourself:
What should happen?
Why should it happen?
What should my meter read?
What does the actual reading tell me?