6.4: Electrical Components and Symbols
- Page ID
- 41475
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Common Components:
- Resistor: Limits current flow.
- Capacitor: Stores electrical energy.
- Relay: Electrically operated switch.
- Transformer: Changes voltage levels.
Analogy Example:
Think of a capacitor like a water tank. It stores water (electricity) and releases it when needed. A transformer is like a water pump that adjusts the pressure (voltage) to the right level.
HVAC Electrical Components and Symbols
HVAC systems rely on various electrical components to control, regulate, and distribute power throughout the system. Understanding how these components function and how they are represented in electrical diagrams is crucial for troubleshooting and installation. This section will cover the most common electrical components in HVAC systems, their functions, and the symbols used in wiring diagrams.
1. Learning Objectives
By the end of this section, you should be able to:
-
Identify and explain the functions of basic electrical components in an HVAC system.
-
Interpret common electrical symbols in schematics and wiring diagrams.
-
Apply component symbols to analyze HVAC wiring diagrams and troubleshoot circuits.
2. Common Electrical Components in HVAC
HVAC systems contain various electrical and electronic components that manage power, signals, and operations. Below are some of the most critical components found in HVAC circuits:
2.1 Resistor: Limits Current Flow
- Function: A resistor reduces or limits electrical current in a circuit.
- Common Use in HVAC: Used in control circuits, variable-speed fan controls, and electronic boards to regulate power.
- Symbol:
Analogy: Think of a resistor like a narrow section of a pipe that restricts water flow.
2.2 Capacitor: Stores and Releases Electrical Energy
- Function: Stores electrical energy and releases it when needed.
- Common Use in HVAC:
✅ Start capacitors provide an initial power boost to compressors and fan motors.
✅ Run capacitors maintain a steady voltage supply to keep motors running efficiently. - Symbol:
Analogy: A capacitor is like a water tank—it stores water (electricity) and releases it when needed.
2.3 Relay: Electrically Operated Switch
- Function: Uses a small electrical signal to control a larger electrical circuit.
- Common Use in HVAC:
✅ Turns compressors, fans, and heating elements on and off.
✅ Allows low-voltage signals from a thermostat to control high-voltage components.
- Symbol:
Analogy: A relay is like a remote-controlled water valve—it allows a small switch to control a large flow of electricity.
2.4 Transformer: Changes Voltage Levels
- Function: Converts high voltage to low voltage or vice versa.
- Common Use in HVAC:
✅ Reduces 120V or 240V AC down to 24V AC for thermostats and control circuits. - Symbol:
Analogy: A transformer is like a water pump—it adjusts the pressure (voltage) to the right level for different parts of the system.
2.5 Contactor: Controls High-Voltage Loads
- Function: Similar to a relay but designed to handle high-voltage loads.
- Common Use in HVAC:
✅ Turns compressors and condenser fans on and off in split systems. - Symbol:
- ⚡
Analogy: A contactor is like a big on/off switch that controls high-power HVAC equipment.
2.6 Thermostat: Temperature Control Device
- Function: Sends a signal to turn heating or cooling equipment on and off based on temperature settings.
- Common Use in HVAC:
✅ Controls furnaces, air conditioners, and heat pumps. - Symbol:
Analogy: A thermostat is like a water faucet with an automatic shutoff—it controls temperature instead of water flow.
3. Common Electrical Symbols in HVAC Wiring Diagrams
HVAC wiring diagrams use standard symbols to represent different electrical components. Below is a reference table of the most commonly used symbols in HVAC schematics:
| Component | Symbol | Function |
|---|---|---|
| Resistor |  |
Limits current flow |
| Capacitor |  |
Stores and releases electrical energy |
| Relay |  |
Controls circuits with a small signal |
| Transformer |  |
Converts high voltage to low voltage |
| Contactor | |
Controls high-voltage loads |
| Thermostat |  |
Controls HVAC systems based on temperature |
Pro Tip: Learn to recognize these symbols in HVAC wiring diagrams to quickly identify and troubleshoot electrical components.
4. Practice & Application
4.1 Matching Symbols to Components
✅ Identify electrical symbols in a wiring diagram and match them to their corresponding HVAC components.
✅ Practice drawing symbols for common HVAC parts to improve memory.
4.2 Labeling Components in a Simple Circuit
✅ Draw a basic HVAC control circuit that includes:
- A thermostat controlling a relay
- A relay switching on a compressor motor
- A capacitor helping start the motor
- A transformer converting 120V to 24V
✅ Label each part with its name, function, and electrical symbol.
5. Conclusion: Why Understanding Electrical Components & Symbols Matters in HVAC
🔹 Recognizing electrical components helps HVAC technicians troubleshoot systems more efficiently.
🔹 Understanding wiring diagrams allows you to quickly diagnose faulty components like relays, capacitors, and transformers.
🔹 Learning electrical symbols and functions makes it easier to read and follow HVAC schematics.
✅ Next time you see an HVAC wiring diagram, try identifying the components and predicting how they function together. Understanding these symbols and their meanings will make you a better, more effective HVAC technician!
Practice:
- Match symbols to their corresponding components on a diagram.
- Label electrical components in a simple circuit.
- Create a table of common components with their symbols and functions.
Instructions for Practice Exercises:
Complete the following exercises to reinforce your understanding of HVAC electrical components and symbols. This assignment will help you recognize electrical symbols, label components in a circuit, and create a reference table for common HVAC components.
Part 1: Match Symbols to Their Corresponding Components
Below are six electrical symbols commonly found in HVAC wiring diagrams. Match each symbol to the correct component name. Write the letter of the correct answer in the blank next to the corresponding symbol.
| Symbol | Component Name |
|---|---|
| 🞇 | A. Transformer |
| ─///─ | B. Resistor |
| ─ | |
| 🞉 🞉 | D. Relay |
| ⚡ | E. Contactor |
| (T) | F. Thermostat |
Bonus (2 Points): Which component controls high-voltage loads in an HVAC system? Write your answer below:
Part 2: Label Electrical Components in a Simple Circuit
Below is a basic HVAC control circuit. The circuit includes:
- A transformer that converts 120V to 24V
- A thermostat that acts as a switch
- A relay that controls the compressor
- A capacitor that helps the motor start
- A resistor that limits current flow
Task:
- Draw a simple circuit diagram that includes all of the above components.
- Label each component clearly using its correct name and symbol.
- Use arrows to indicate the direction of current flow in the circuit.
Hint: The thermostat sends a signal to the relay, which activates the compressor. The capacitor helps the compressor start, and the resistor limits excess current.
Part 3: Create a Table of Common Components with Symbols and Functions
Fill in the table below by completing the missing symbols and functions for common HVAC electrical components.
| Component | Symbol | Function |
|---|---|---|
| Resistor | ?? | Limits current flow in a circuit |
| Capacitor | ?? | Stores and releases electrical energy |
| Relay | ?? | Controls circuits with a small signal |
| Transformer | ?? | Converts high voltage to low voltage |
| Contactor | ?? | Controls high-voltage loads in HVAC systems |
| Thermostat | ?? | Turns heating or cooling systems on/off based on temperature |
Bonus (3 Points): Why does an HVAC system need both a capacitor and a relay? Explain in 1-2 sentences:
✅ Completed assignments to reinforce what you learn.
✅ Use your HVAC textbook or class notes if you need assistance and ask for help if you get confused.
This exercise reinforces electrical theory, HVAC component identification, and wiring diagram reading skills. Students should practice drawing, labeling, and explaining HVAC electrical circuits to build confidence in troubleshooting.