A2L/Crosswalk
A2L/Crosswalk

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The field guide

The rules and numbers a residential tech gets asked about on the job — which refrigerant, which date, which minimum, how cold. Every figure has its federal source next to it, so you can cite it instead of arguing about it.

RefrigerantsRulesRatingsClimateEquipmentService
The refrigeration cycleRefrigerant flows in a loop: evaporator (indoors, absorbs heat) to compressor (raises pressure) to condenser (outdoors, rejects heat) to metering device (drops pressure) and back. The compressor and metering device divide the high-pressure side from the low-pressure side.LOW-PRESSURE SIDEHIGH-PRESSURE SIDEcold · indoorshot · outdoorsEVAPORATORindoor coilHEAT INfrom room airCONDENSERoutdoor coilHEAT OUTto outside airCOMPRESSORraises pressure — the only part that uses real powerMETERING DEVICETXV or piston — drops the pressurelow-pressurecold liquid + vaporlow-pressurecool vaporhigh-pressurehot vaporhigh-pressurewarm liquidNothing here makes cold. Heat is moved from the left coil to the right coil.
RefrigerantsRefrigerant quick referenceR-22, R-410A, R-32 and R-454B side by side: what is in each one, safety class, GWP, and where it stands today.Read →RulesR-410A: what is banned and what is notThe three dates people mix up — manufacture, installation and service — with the federal rule behind each one.Read →RatingsSEER2, EER2, HSPF2 and the federal minimumsWhat each rating measures, the DOE minimum for your state, and what ENERGY STAR and Cold Climate require on top.Read →ClimateWinter design temperature by cityThe cold day you design for, in 169 U.S. cities across every state — and how to read it against a heat pump’s certified capacity.Read →RulesEPA 608 at a glanceThe four certification types, what each one lets you work on, and the rules every technician is held to.Read →EquipmentHow to read a nameplateModel, refrigerant, charge, MCA and max fuse — which line answers which question, on one labeled drawing.Read →EquipmentHow a heat pump moves heatThe refrigeration cycle, the reversing valve, and where every part of a split and a mini-split lives.Read →ServiceWhere to find replacement partsParts follow the manufacturer, not the label: who makes which brand, the official parts channel for each, and what to have in hand.Read →ServiceWhat usually fails, and what the repair involvesThirty-five documented failure points on heat pump systems — symptom, usual cause, what the fix takes and who is allowed to do it.Read →ServiceSafety recalls: residential HVAC since 2010Every CPSC recall of residential heat pumps, air handlers, coils, packaged units and furnaces — models, hazard and remedy, in CPSC’s own words.Read →ServiceCoil leaks and TXVs: three court-approved settlementsWhat the court records say about the Lennox, York and Trane class settlements — who was covered, what was alleged, what the manufacturer answered.Read →