It's January. 11:47 pm. The outdoor coil is a block of ice, the pressures look fine, and the homeowner is watching you through the kitchen window. You've been in HVAC for years. You know refrigeration. You know electricity. And right now you've got no idea what's wrong with this machine, because it's a heat pump and it doesn't behave like anything you were trained on. That isn't a competence problem. It's a mental-model problem. Most techs learned on air conditioning, where heat moves one way. A heat pump reverses. That one fact changes how you read the gauges, which charging method is valid for the conditions, what a defrost failure looks like, and how you size the equipment in the first place. Heat Pumps Field Guide rebuilds the model, chapter by chapter: How a heat pump actually works in heating mode, including O vs. B wiring and the aux-heat settings that run up the billA2L refrigerants: R-32 vs. R-454B on the gauges, the tools that have to change, and the leak-detector shutdown that fakes a no-heat callRefrigerant charge: which method applies, when, and why the weigh-in is the only honest answer in JanuaryManual J and Manual S sizing, and the cold-climate complication at design temperatureDefrost diagnostics: force a cycle, watch every component, find the sensor that liesReversing valve testing: electrical, mechanical, then internal leakage, before you cut anything outCold-climate systems: capacity data, balance point, dual-fuel changeover and lockoutsDuctwork: static pressure, airflow checks, and when ductless is the better answerInverter and communicating systems: DC bus safety, operating point first, fault codes as evidenceSelling the heat pump: rebates that still exist, operating-cost math, and a payback conversation that survives a skepticCommissioning and documentation that hold up when a dispute landsEvery chapter ends with a field deliverable, such as a defrost diagnostic flowchart, an A2L transition checklist, a balance point worksheet or a 24-item commissioning sign-off. It's built to live on the truck, not the shelf. What's new in the Second Edition: all eleven chapters rewritten and expanded, every figure re-checked against EPA rules, OEM installation manuals, ACCA, AHRI, ENERGY STAR, DOE and national-lab research, and the sales chapter rebuilt now that the federal Section 25C credit is gone. Where the trade repeats a number nobody can source, this book says so. Who it's for: residential and light-commercial technicians, service managers training a crew, and contractors who want fewer winter callbacks. Homeowners looking for a DIY repair guide should look elsewhere. About the author: JD R. Lawson is a licensed mechanical engineer with 25+ years of HVAC work across the Philippines, Japan and the U.S. He built an HVAC company from zero to acquisition and still consults for it. He writes the way he talks on a job site. The market moved faster than the training. This book is how you catch up.
