Diagnose it. Don't guess it.
Deterministic HVAC-R fault diagnosis for working field techs. Pressures in, ranked faults out — with the reasoning and the industry standard behind every step. Real guidance under pressure, no probes required to start.
Most diagnostic apps guess. This one shows its work.
Three maybes and a shrug
Every other app throws three possible faults on the screen with no explanation and expects you to pick one. That's not a diagnosis — that's a coin flip with extra steps.
An AI you can't audit
The new wave of AI assistants can hand you a confident answer — swap a $400 TXV — with no reasoning you can check, cite, or defend. A guess you can't audit is worse than no guess.
PT charts in a glovebox, math in your head
The tools that don't guess instead make you do everything by hand. Lookup. Interpolate. Subtract. Re-check. On a 100°F rooftop with a customer waiting.
The Diagnostic Pro difference
Deterministic, not probabilistic
A weighted scoring engine — not an LLM — ranks every fault on every call. Same inputs always give the same answer, and the reasoning is right there next to the score.
Pre-check gate before any reading
The app blocks the diagnosis until airflow, coil, blower, and stabilization are confirmed. Bad readings in, bad faults out. We won't let you.
Built around your hands
Glove-friendly tap targets. Industrial dark UI. Big numbers, no fluff. Works offline so basements and rooftops aren't a problem. Designed for the truck, not the office.
Other tools stop short. Determinari finishes the diagnosis.
We don’t name names — but you already know the categories. Here’s where each one leaves you, and where Determinari keeps going.
Probe-locked apps
Gate the real value behind $300+ wireless probes. No probe synced, no diagnosis — and a dead Bluetooth link can stall the whole call.
Determinari: A full ranked diagnosis from manual readings — no probe to pair and no dead link to stall the call. Works with every tool brand, on any phone.
AI-guess apps
Even the new “measurement-aware” AI hands you a black-box confidence score — or a confidently wrong part — with no reasoning you can audit, cite, or defend to a customer.
Determinari: A deterministic engine shows every indicator behind the call, and the published standard behind every number. Same inputs, same answer, every time — nothing you can’t back up.
PT-chart calculators
Give you superheat and subcooling, then stop. You still interpret the fault in your head on a hot rooftop with a customer waiting.
Determinari: Carries the reading all the way to a ranked, evidence-backed fault — and the next verification step to confirm it.
Back-office field-service software
Built for dispatch, invoicing, and the office. Powerful for the calendar, but there's no diagnostic brain in the truck.
Determinari: The diagnostic layer those tools lack. Runs right alongside them — focused on the call, not the schedule.
Five senses, in the right order
Before you read a single pressure, the app walks you through the checks a senior tech would do on instinct.
Pre-check gate
Before any pressure gets entered, the app walks you through visual inspection, airflow, coil cleanliness, filter, blower, and stabilization. Skip a step and the diagnosis button stays disabled. The cheap stuff hides expensive symptoms — this catches them first.
Live SH / SC engine
Nine refrigerant libraries — R-410A, R-22, R-32, R-454B, R-134a, R-404A, R-407C, R-422B, R-507A — with linear interpolation. Punch in your pressures and temps; superheat, subcooling, and saturation temps update live as you type. A2L refrigerants are flagged automatically.
Ranked faults, with the reasoning
A weighted engine ranks seven fault models — undercharge, overcharge, liquid line restriction, metering device restriction, airflow issue, non-condensables, normal operation — by confidence. Each ranking shows the indicators that produced it, so you can disagree with the engine and still leave the call right.
Senior Tech mentor, on demand
Once the engine names the fault, an optional AI mentor explains the call like a 25-year veteran would — why the numbers point there, what to verify first, how the repair usually goes — with manual citations badged by source, OEM or third-party. It never re-diagnoses: the deterministic engine's ranking is the verdict, and the mentor's only job is to walk you through it.
Symptom matrix & quick calcs
A printable, glove-friendly cheat sheet of every common fault signature on every refrigerant. Quick calcs for target superheat (TXV vs. fixed orifice), capacity, delta-T, and rule-of-thumb sanity checks. The reference card you wish was in the truck.
Plate camera & parts sourcing
Snap a photo of the data plate — the app reads model and serial, looks up specs, and surfaces matching parts across five major suppliers in one place. Get the right capacitor on the truck before you finish writing the invoice.
Owner-built workflows
Shop owners author custom, step-by-step workflows — startup checklists, PM routines, brand-specific procedures — and push them to every tech's app. A new hire runs the senior tech's playbook on day one, and every truck follows the same gold-standard process on every call.
Service reports, customer-ready
Every diagnostic exports as a printable service report in plain language — what was checked, what was found, what was fixed. The kind of paper trail that defends the invoice and earns the next call.
Offline first
Basements. Rooftops. Equipment rooms. The whole engine runs without a signal — saved jobs and diagnostics sync the moment you're back in range. No bars, no excuses.
Every call, traceable to a published reference.
Charging targets, ventilation, refrigerant handling, electrical, gas — each area of the app maps to the documentation the trade is actually held to. So you can defend the invoice, satisfy the warranty desk, and train a green tech off the same page.
The refrigerant transition is here. The app already speaks it.
As the industry moves to next-generation A2L refrigerants, every tech is suddenly charging and troubleshooting systems they've never touched. The PT numbers are different. The handling rules are different.
Determinari shipped R-32 and R-454B from day one — full PT libraries with linear interpolation, the same deterministic SH/SC engine, and the ASHRAE A2L class flagged automatically wherever it appears. No add-on, no update to wait for, no relearning the tool.
Walk up to an A2L system with the same certainty you have on R-410A.
Flagged as A2L (mildly flammable) automatically throughout the app — so the safety class is in front of you before you connect a hose, not buried in a spec sheet.
Nine refrigerants, named.
Every refrigerant the SH/SC engine computes — spanning legacy, current, and next-gen A2L — each with linear interpolation and its ASHRAE safety class flagged.
Every seat. Every feature. Every refrigerant.
No paywalled fault models. No "pro tier" for the math.
Honest pricing. No free tier.
Subscription-only: $29 a month or $290 a year. No free trial, no tiers, no upsells — subscribe and you're in. The PT chart and SH/SC calculators are free for everyone — the subscription is for the diagnostic engine.
Frequently asked questions
Diagnose it. Don't guess it.
Every feature, every refrigerant, every update — $29 a month or $290 a year. No free tier; subscribe and start diagnosing.