The laminated refrigerant diagnostic quicksheet every tech has used — digitized, sharpened, and backed by published research instead of guesswork.

Enter what you actually measured. Get ranked, explained, cited answers. Works with no signal, in a mechanical room, on a roof, at 2am.

WHAT IT DOES

• Ranks likely faults from your readings — superheat, subcooling, pressures, temperature splits, amps, and dozens of optional advanced measurements
• Explains WHY each fault is ranked where it is, and what evidence argues against it
• Tells you the single highest-value next measurement instead of dumping a checklist on you
• Stops cold on safety hazards before it will diagnose anything

BUILT FOR THE TECH STANDING IN FRONT OF THE UNIT

Start with a complaint alone and get a preliminary read. Add one reading and watch it sharpen. There is no mandatory questionnaire and no wizard to sit through — enter what you have, in any order, and it recalculates as you go.

Guided mode walks an apprentice through the highest-value readings in the order a tech actually takes them. Full mode gives an experienced hand every field at once.

HONEST BY DESIGN

Most diagnostic tools always produce an answer. This one will tell you it does not have enough to be sure — and that is deliberate.

• Confidence never exceeds the evidence behind it
• "Not enough verified information — do this first" is a legitimate, first-class result
• Readings that disagree with each other get flagged, not averaged away
• When your gauges may be lying to you, it says so

EVERY RULE CITES A REAL SOURCE

Thresholds, weights and gates come from published manufacturer and trade literature — HVAC School, ACHR News (Tomczyk), Copeland application bulletins, Sporlan bulletins, Danfoss Fitters Notes, BITZER, NIST and ASHRAE. If a rule cannot be cited, it does not ship. Tap through to see what a given answer rests on.

NOT AN AI CHATBOT

This is a deterministic rules engine. The same inputs always produce the same output. Nothing is generated on the fly, nothing is invented, and nothing is sent anywhere. You can hand it the same session next year and get the same answer.

WORKS COMPLETELY OFFLINE

No account. No sign-in. No network calls at runtime. No analytics. No ads. The entire knowledge base ships inside the app.

SAFETY FIRST, WRITTEN FOR SOMEONE WORKING ALONE

Safety gates fire before any diagnosis is offered — high discharge temperature, suspected burnout and terminal venting, A2L and A3 flammable refrigerant handling, and B-class toxicity escalation. Messages are written for an apprentice reading them alone, not for someone who already knows the answer.

COVERAGE

30 refrigerants including R-410A, R-454B, R-32, R-404A, R-407C, R-448A, R-449A, R-438A and R-22, with correct dew/bubble handling on glide blends. Split systems, packaged units, walk-ins, racks, chillers and water-cooled condensers. Comfort cooling, medium temp and low temp application bands.

A NOTE ON WHAT THIS IS NOT

This is not an equipment database, a parts lookup, or a manual library. It does not replace your judgment, your gauges, or your training. It is a second opinion that shows its work.

HONE Builds — tools by a working HVAC tech, for working HVAC techs.