Level 1, Unit 4, Section 1 – Introduction to Electricity

Unit 4 — Electrical Fundamentals

Section 1 — Introduction to Electricity

Section 1 Overview

This section develops the introductory electrical knowledge required of Level 1 Refrigeration and Air Conditioning Mechanics (313A/313D). The focus is on practical application — understanding how electrical energy is produced, controlled, and safely used to power motors, compressors, fans, heaters, controls, and safety devices in residential, commercial, and light industrial HVAC/R equipment.

1.0.1 — General Learning Outcomes

Upon successful completion of this section, the apprentice will be able to:

Describe the fundamental electrical quantities — voltage, current, resistance, and power — and apply Ohm’s Law and the power formula to calculate unknown values.
Identify common circuit components (resistors, conductors, protection devices) and select conductors based on ampacity and insulation requirements.
Describe series, parallel, and combination circuit configurations, distribution panels, and overcurrent protection devices, including CEC motor protection rules.
Describe the construction and operation of relays, switches, contactors, and transformers, and explain how each is applied within HVAC/R power and control circuits.
Read and interpret schematic (ladder), wiring, and block diagrams, and apply a systematic six-step troubleshooting method to locate and confirm electrical faults.
Perform series, parallel, and combination circuit calculations and demonstrate correct procedures for measuring voltage, current, resistance, and power with a multimeter and clamp meter.
Describe electronic control boards, variable-frequency drives (VFDs), ECM motors, thermistors, pressure transducers, and humidity sensors, and explain the diagnostic approach for each.

1.0.2 — Section 1 — Lessons at a Glance

Section 1 builds from the physics of electricity through circuits and components to the practical measurement and calculation skills applied every day on the job.

1.1

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Electrical Quantities

Core electrical terms, voltage, current, resistance, power, AC vs DC, Ohm’s Law, the power formula, and SI units and schematic symbols used in HVAC/R.

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1.2

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Circuit Components

Resistors, conductors (copper vs aluminum, solid vs stranded), AWG ampacity tables, derating rules, and insulation types including wire selection for HVAC/R applications.

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1.3

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Circuits, Panels & Protection

Series, parallel, and combination circuits. Distribution panels (single- and three-phase). Overcurrent protection devices and CEC motor protection coordination rules.

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1.4

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Relays, Switches, Contactors & Transformers

Switch types (NO/NC), relay contact configurations and ratings, contactor construction, and transformer turns ratio and VA burden. Worked examples for each.

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1.5

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Wiring Diagrams & Basic Troubleshooting

Ladder, wiring, and block diagrams. The four fault types (open, short, ground, overload). Systematic six-step troubleshooting and the voltage-drop method on ladder rungs.

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1.6

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Calculating & Measuring

Series, parallel, and combination circuit calculations with worked examples. Safe multimeter and clamp meter techniques for voltage, current, resistance, and power measurement.

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1.7

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Electronic Controls & Sensors

Control board inputs, logic, and outputs. VFDs and ECM motors. NTC and PTC thermistors, pressure transducers, airflow switches, and humidity sensors — operation and diagnostics.

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1.0.3 — Key Terms — Section 1 Preview

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Voltage (EMF)

The electrical pressure that drives current through a circuit. Measured in volts (V). In HVAC/R, common values are 24 V (control), 120 V, 208/230 V (single-phase power), and 208/460 V (three-phase power).

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Current (Amperage)

The rate of electron flow through a conductor. Measured in amperes (A). Motor nameplates list full-load amps (FLA) and rated-load amps (RLA) as the expected operating current draw.

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Resistance

Opposition to current flow. Measured in ohms (Ω). Conductors have low resistance; insulators have very high resistance. Motor winding resistance is checked to detect open or shorted coils.

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Ohm’s Law

The fundamental relationship: V = I × R. Knowing any two quantities allows calculation of the third. Applied whenever voltage drop, current draw, or conductor resistance needs to be verified.

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Power (Wattage)

The rate of doing electrical work. P = V × I (watts). For AC circuits, true power accounts for power factor: kW = kVA × PF. Measured with a wattmeter or calculated from voltage and current readings.

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Transformer

Steps voltage up or down using electromagnetic induction. In HVAC/R, the 24 V control transformer steps 120 V or 208/240 V down to 24 V for thermostat and control circuits. Turns ratio determines the voltage ratio.

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Contactor

A heavy-duty relay that switches high-current loads such as compressor motors. The control coil (typically 24 V) pulls in the contacts to complete the power circuit. Pitted contacts increase resistance and cause voltage drop.

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Overload Protector

A thermal or electronic device that opens the circuit when current exceeds a safe limit, protecting motor windings from heat damage. Overloads that trip repeatedly indicate an underlying mechanical or electrical fault.

1.0.4 — Why Electrical Fundamentals Matter in HVAC/R

Every refrigeration and air conditioning system is both a refrigerant system and an electrical system. The compressor, condenser fan, evaporator fan, defrost heater, thermostat, reversing valve solenoid, and every safety switch are all electrical loads connected by wiring and controlled by circuits. A technician who cannot read a wiring diagram, measure voltage, or calculate expected current draw cannot diagnose electrical faults — and electrical faults account for a large proportion of all HVAC/R service calls.

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How Section 1 Connects to the Rest of Unit 4

The concepts introduced here — Ohm’s Law, circuit configurations, component function, and diagram reading — are the foundation for everything that follows in Unit 4. Later sections apply these fundamentals to motor starting methods, single-phase and three-phase power, control circuits, and electrical troubleshooting procedures.

Before this unit, Units 1–3 focused on refrigerant-side fundamentals: the vapour compression cycle, thermodynamic properties, and system maintenance. Unit 4 shifts the lens to the electrical systems that drive and control the refrigerant circuit. By the end of Section 1, reading a wiring diagram and taking systematic electrical measurements will be standard practice.