HVAC/R field app · works with no signal
Know what your gauges are telling you.
Superheat and subcool with a live verdict, P-T and pressure enthalpy charts for eleven refrigerants, airflow, a psychrometric chart, load calcs, mini-splits and a full refrigeration tab — plus Gary, an assistant who answers in shop talk. All of it runs on your phone, offline.
Free web app for any phone or computer. Android app available, iPhone & iPad app on the way. No account, no sign-in.
Actual screens from the app
- 11refrigerants
- 400+Gary topics
- 95troubleshooting cards
- 31HVAC Basics lessons
- 41how-to guides
- 0bars of signal needed
The tools
Everything you'd pull out of the truck, on one screen.
Each tool opens from the menu, remembers what you typed, and switches between °F and °C with every temperature in the app.
New · Pressure Enthalpy Chart
See the whole cycle on one chart.
Enter suction and head pressure, suction line and liquid line temperatures, and Thermal Gauge draws your system on a real P-h chart for that refrigerant — the saturation dome, the four points and the cycle between them.
Pressure Enthalpy Chart
All eleven refrigerants, with temperature, quality and entropy lines. Tap anywhere on the chart to read the point, or zoom to your cycle.
A real psychrometric chart
Relative humidity, absolute humidity, moisture capacity of the air, dew point, wet bulb and enthalpy — with your indoor and outdoor air plotted.
Gary reads P-h charts
"R-22, 68 suction, 250 head — what's the COP?" He works the cycle and explains each number in plain words.
Gas furnace data tags
Snap a furnace rating plate and Gary pulls out input and output BTU, efficiency, manifold and inlet gas pressures, temperature rise and gas type.
HVAC Basics
31 short lessons with diagrams and a quiz for each — the refrigeration cycle, furnace sequence, electrical and airflow.
iPhone & iPad
A native app for iPhone and iPad is on the way. Until then, the web app works on both — add it to your Home Screen.
Refrigeration
Ice machines, freezers and fridges.
A whole tab for the boxes that keep food cold. Pick Ice Machines, Freezers or Fridges for how they work, the numbers to expect, the parts that fail and what to check first.
Evaporator TD
Suction pressure and box temperature in, saturated suction and TD out, with a verdict for freezers and coolers.
Freeze-cycle check
Compare your freeze and harvest times with the maker's chart and get the likely causes when they're off.
Refrigeration refrigerants
R-448A and R-449A from the makers' tables, plus R-290 and R-600a — in every picker, the P-T chart and Gary.
Gary knows refrigeration
Defrost, pump-down, head pressure control, EPR/CPR, oil safeties, CO2 racks, home fridge controls and ice machine set-up.
Troubleshooting
Iced coils, warm boxes, short cycling, sight-glass bubbles, leaking ice machines, sweating doors and frozen drains.
Walk-ins & hydrocarbons
Interior releases, R-290 and R-600a flammability, flame-free repairs and food-safety temperatures.
Ask Gary
An assistant that talks like a tech.
Gary works with no internet and no account. Type or say what you're seeing — readings, symptoms, slang, typos — and he tells you what it means and where to start. Every answer comes from the app's built-in reference, so it works in a basement with no bars.
Pressures & charge
Reads a whole set of gauge readings, works out superheat and subcool, and gives normal pressures for today's outdoor temperature.
Troubleshooting
Symptom to cause with a "start here" step: frozen coils, short cycling, lockouts, noises, smells — plus mini-splits, walk-ins, fridges and ice machines.
Meter readings
"0 V between Y and C at the condenser" — he tells you which switch is open and what to check next.
Component change-outs
Compressors, evaporator coil pulls, heat strips, blower motors, gas valves, igniters — what to match and every step.
Package units & water-source
Gas packs, rooftop units, belts, draw-through traps, WSHP lockouts, water flow and 500 × GPM × ΔT.
Data tags from a photo
Snap a condenser nameplate, a gas furnace rating plate or your gauges and Gary reads them — model, serial date, refrigerant, BTU input and gas pressures. Photos never leave the phone.
Pressure Enthalpy
Plot a cycle from four readings, work out COP, flash gas and heat of rejection, and explain what each part of the chart means.
Psychrometrics
Relative vs absolute humidity, moisture capacity, dew point and how to read a psychrometric chart — with numbers from your readings.
Mini-splits
Ductless and multi-zone: S1-S2-S3 wiring, charging by weight, safe pump-down, inverter boards, cleaning heads, defrost and error codes.
Refrigeration
Ice machines, walk-ins, reach-ins and home refrigerators — defrost, pump-down, sight glasses, oil safeties, CO2 and more.
Thermostats & air handlers
Thermostat types and wiring, outdoor thermostats, dual fuel, sequencers, blower motors and furnace parts.
Safety first
Gas smells, CO, flames and refrigerant exposure get emergency steps before anything else.
Conversions & formulas
CFM and BTU from a temperature split, 500 × GPM × ΔT, kW to BTU, °F to °C and P-T lookups by voice or text.
Refrigerants & blends
P-T lookups for every refrigerant in the app, bubble and dew points for blends, glide, and which oil goes with which refrigerant.
Furnaces & ignition
Sequence of operation, flame sensors, igniters, pressure switches, gas pressures and venting.
Student Mode
Built for the classroom and the trainer.
Turn on Student Mode in Settings and three tabs appear: HVAC Basics, 31 lessons with diagrams and quizzes; Faults, 40 troubleshooting exercises in four tiers; and How To, 41 step-by-step guides for the skills every new tech needs.
New · HVAC Basics
The things every tech should know, one lesson at a time.
Short lessons in four units, each with a diagram where it helps, the key terms and a four-question quiz. Pass three of four to check the lesson off; progress stays on the phone.
The AC isn't coming on at all.
Look, listen and check the basics. Few or no tools.
The furnace starts making noise but never lights.
Meter work: find the part that stopped the call or the power.
When I turn the fan to ON, the outside unit starts too.
Gauges, temperatures, amps and line voltage together.
Poor cooling, and the small copper line outside feels oddly cold.
Subtle and combined faults. Readings have to be interpreted, not just read.
Set safely. Every fault is set by an instructor with the power locked out, using entry-level tools. None of them vent refrigerant, open gas piping or bypass a safety — and each one has run-time and stop limits. An instructor view shows the setup; students get three hints, then the answer.
41 How To guides, including
- Read a wiring diagram
- Check for voltage
- Lockout / tagout
- Braze copper
- Make a flare
- Charge refrigerant
- Recover refrigerant
- Pressure test & evacuate
- Check gas pressure
- Clean coils
- Water-source heat pumps
- Adjust a blower belt
- Thermostats
- Clean an ice machine
- Walk-in defrost & TD
- Fridge not cooling
- Pump-down control
- Install a mini-split
- Pump down a mini-split
- Deep-clean a mini-split head
Themes
Make it yours. Six looks, one tap.
Pick a theme in Settings. Every theme gets the same clean, simple layout — only the colors change.
Built for the field
Attic, crawlspace, rooftop — no signal needed.
Fully offline
Every calculator, chart, guide and Gary answer is stored on the phone. Nothing waits on a connection.
Private
No account to create. Photos of data tags and gauges are read on the phone and never uploaded.
Service notes
Save notes with photos and labels for each job, and copy them into a text or email in one tap.
Voice both ways
Ask Gary with the mic when your hands are dirty, and have him read the answer out loud.
Get Thermal Gauge
On your phone in a minute.
Web app
Any phone or computer
Open it in your browser. It keeps working offline after the first visit.
Open the web appiPhone & iPad · Android
Install it like an app
iPhone & iPad: Share → Add to Home Screen.
Android: browser menu ⋮ → Install app.
Android app
Want the installer?
Ask for the Android app, or send feedback and feature requests.
Contact usField reference only — not a substitute for training. Always follow the equipment manufacturer's instructions, EPA and OSHA standards, and local codes. Electrical, gas and refrigerant work should only be done by qualified technicians.