Stop memorizing the NUMBERS KNOW THE WHY
Superheat, subcooling, 500 microns, the PT chart: every number on the job has a reason behind it. Learn the reason with free practice quizzes, plain-language Field Notes and The Code.
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Read the reference, test yourself, or start with a short article. All of it is free.
The Code
Eight chapters, from the PT chart and charging to vacuum, airflow, A2L refrigerants and gas heat, each one cited to its source.
Read The Code
Practice quizzes
14 quizzes of 10 questions each, from the refrigeration cycle to gas furnace ignition. Every answer comes with the reason behind it.
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Field Notes
Plain-language articles on the calls that come up most: no-cool triage, run capacitors, flares, recovery cylinders and more.
Read Field NotesThe figures behind the rules
Three numbers from the CDC, the Department of Energy and the EPA, each tied to a chapter of The Code.
Americans die each year from unintentional carbon monoxide poisoning not linked to fires.
Gas heat in The Code →How much less energy an air conditioner can use when its air filter is routinely replaced or cleaned.
Airflow in The Code →Source: U.S. Department of Energy, Energy Saver 101: Home Cooling
The GWP limit for refrigerant in new US residential AC and heat pump systems made or imported since January 1, 2025.
Refrigerant rules in The Code →Source: U.S. EPA, Technology Transitions restrictions by sector
Know what moves a reading, and the right number stops being something you have to memorize.
HVAC Resource
Short reads for real service calls
Plain-language articles on the readings and calls that trip people up.
HVAC know-how, in plain language.
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14 free practice quizzes
Ten questions per topic, from the refrigeration cycle to gas furnace ignition.
Free · No account needed · Every answer explained