System
Suction line (low side)
Liquid line (high side)
TXV target
Use the subcool listed on the outdoor unit's data plate. 8–12 °F is typical when not listed.
Results
Charging curve
Required CFM from tonnage
Lower CFM/ton removes more moisture (humid climates); higher CFM/ton gives more sensible capacity (dry climates).
Indoor ambient
Outdoor ambient
Indoor results
Outdoor results
Enthalpy split
A bigger split means more total heat (sensible + latent) the system has to reject — pairs with the Required Airflow tab's sensible-only numbers.
Sends indoor wet bulb & outdoor dry bulb straight into the SH/SC tab's piston superheat target.
Pressures in psig. Values below 0 psig shown in inHg vacuum. Blends: use bubble (liquid) for subcool, dew (vapor) for superheat.
🚨 Emergencies
- Smell gas: no switches, phones or flames inside. Get everyone out, shut the gas at the meter if safe, call the gas utility / 911 from outside.
- CO 70 ppm or more: everyone out and call 911. 36–69 ppm: ventilate and shut off sources. 9–35 ppm: tell the customer and ventilate.
- Electric shock: don't touch the person until the power is off. Call 911; start CPR / use an AED if trained.
- Refrigerant on skin or eyes: get to fresh air; warm (not hot) water on skin — don't rub; flush eyes 15 minutes; get medical help.
- Heat stroke (confusion, hot dry skin, collapse): call 911 and cool them down right away.
- Burns: cool running water for 10+ minutes; get help for large or deep burns.
Before every job
Checks clear by themselves each new day.
General field safety guide. Always follow OSHA rules, your company's safety program, the equipment manufacturer's instructions and local codes.
Pressure diagnosis chart
Typical readings vs. normal for each fault. SH on piston systems; TXVs hold superheat until they run out of range.
▲ high ▼ low ● normal two symbols = either
Theme
Temperature units
Changes every temperature in the app, including the P-T chart. Pressures stay in psig; airflow stays in CFM and BTU/h.
Motion
Turns off menu slides, fades and button animations. Everything appears instantly.
Ask Gary voice
Gary speaks each answer using your phone's text-to-speech. Tap the 🎤 in Ask Gary to ask by voice.
Gary uses a male English voice if your phone has one, otherwise a deeper pitch. On iPhone you can add voices in Settings → Accessibility → Spoken Content → Voices → English.
The 🎤 button uses your phone's speech recognition and may need a signal. If it doesn't work, tap the microphone on your keyboard instead.
Student Mode
Adds Faults and How To to the Menu: 40 practice troubleshooting faults in 4 tiers (Beginner to Expert Technician), and step-by-step guides for the basic skills every tech needs.
Developer
About
Thermal Gauge v1.57 (web) · Field reference only. Always follow the equipment manufacturer's instructions.
Gary's photo reading uses Tesseract OCR (Apache-2.0) and runs entirely on this phone — photos never leave it.
🛠️ Developer Settings
Unlocked for this visit. Leaving this page locks it again.
App info
Feature switches
Developers Theme
Only available here. Picking a normal theme in Settings (or the Northern Lights easter egg) turns the developer theme off.
Diagnostics
Error log
Home
House
Design conditions
Use your area's 1% summer / 99% winter design temperatures (local code or ACCA tables), not record highs and lows.
Construction
Windows
Leave all four blank to assume glass equal to 15% of the floor area, spread evenly. A typical window is about 15 sq ft.
Results
Estimate only. For equipment selection, confirm with a full ACCA Manual J, and size equipment with Manual S.
Tap an item to mark it: ✓ OK → ! Needs attention → N/A → clear. Only marked items (and any readings you type) go into the note.
Checklist notes
Adds to the note you're working on, or starts a new note marked "Maintenance / tune-up". The checklist clears once it's added.
⚠️ Safety rules — read before setting any fault
Shows how to set each fault, its safety limits and the answer. Turns off when you leave this page.
Practice only, on equipment an instructor has approved. Always follow the manufacturer's instructions, lockout/tagout, and your school's safety rules.
Learning reference for students. Practice under an instructor, and always follow the manufacturer's instructions, local codes, EPA Section 608 and OSHA rules.
Backup
Notes are saved on this phone only. Removing Thermal Gauge from your Home Screen or clearing website data deletes them. Copy them out now and then to keep a backup.
New service note
Photos & videos
Take a photo or video, or pick one from your photo library.
Field reference only. Always follow the equipment manufacturer's charging instructions.