Learn HVAC properly — from fundamentals to field diagnostics.
Structured HVAC documentation, diagrams, diagnostics and practice — from the refrigeration cycle to furnace sequence of operation, charging and troubleshooting.
Documentation, diagrams and search are free. HVAC Pro adds practice, scenarios and the AI Tutor.
Documentation first
Every topic answers what it is, why it matters, where it's used, how it works, what goes wrong, and how to diagnose it.
Diagrams and readings
Cycle diagrams, sequences of operation, control circuits and airflow — plus what each measurement is telling you.
Symptom-first diagnostics
Start from what the equipment is doing, work through likely causes, and let the checks narrow it down.
Practice and AI Tutor
Questions, quizzes, troubleshooting and equipment scenarios, and a tutor that knows the page you're reading.
Engineering Tools & Calculators
A free universal unit converter plus HVAC calculators for superheat, subcooling, CFM, duct sizing, voltage drop, heat loss, combustion air and more — each with formulas and worked examples.
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Carbon Monoxide Safety
Where carbon monoxide comes from, how it is measured, and what to do when readings are elevated.
Concept
Digital Manifold
Pressures, saturation temperatures, superheat and subcooling from one instrument.
Tool
Gas Furnace
How a modern forced air gas furnace proves each condition before it allows the next step.
Equipment
Gas Furnace: No Heat
The furnace is calling for heat but the burners never light, or they light and then shut down.
Troubleshooting
Heat Transfer
Conduction, convection and radiation, and why every HVAC system is really a heat moving machine.
Concept
Multimeter
The core electrical instrument, what each function measures, and how to use it safely.
Tool
Refrigerant Charging
A measurement driven approach to charging, using the method the metering device calls for.
Procedure
Run Capacitor
What a run capacitor actually does for a motor, and how to tell when it has failed.
Component
The Refrigeration Cycle
How a vapor compression system moves heat from where it is not wanted to where it can be rejected.
Concept
Safety and local code
This is educational reference material. It never presents bypassing safety controls, unsafe energized work, improvised repairs, or improper refrigerant handling as normal practice. Installation, venting, combustion air, gas piping, clearances, electrical requirements and permits vary by jurisdiction, adopted code edition and equipment — always verify local code and the manufacturer's instructions.