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HVAC field diagnostics

Field diagnostics that show their work

You take the readings. TunePro grades superheat and subcooling against the target for the system in front of you, ranks what those numbers point to, and shows you the evidence on both sides — so you can disagree with it.

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The diagnostic side of the phone app needs neither button. No account, no card, no trial clock.

What a conclusion looks like

A verdict you can argue with

Below is the card the app draws when subcooling reads 2°F against a 10°F target and superheat reads 25°F against a 10°F target. It is transcribed word for word from the screenshot next to it, so you can check one against the other.

Higher up that same screen the app is holding something back: Attention — add outdoor temperature to separate a real fault from cold weather or a hot day. It would rather tell you what it is missing than guess past it.

Possible undercharge

moderate indication

Subcooling is low, meaning the condenser is short of liquid — the charge metric on a TXV system.

What points here

  • Subcooling 2°F vs target 10°F — low — condenser short of liquid.
  • Superheat 25°F vs target 10°F — high — coil starved.

What argues against

Nothing in these readings argues against it.

What to check next

  • quick Read subcooling against the nameplate value.
  • quick If this system has a sight glass, confirm the liquid line runs full with no flash bubbles; most residential splits have none, in which case skip this one.
  • quick Add outdoor temperature to rule out cold-weather operation before touching charge.
The Diagnostics screen showing a "Possible undercharge" card at moderate indication, with its evidence panel open: what points here lists subcooling 2 °F against a 10 °F target and superheat 25 °F against a 10 °F target, what argues against says nothing in these readings does, and what to check next lists three quick checks. The Diagnostics screen showing a "Possible undercharge" card at moderate indication, with its evidence panel open: what points here lists subcooling 2 °F against a 10 °F target and superheat 25 °F against a 10 °F target, what argues against says nothing in these readings does, and what to check next lists three quick checks.
The same card, in the app.

Three things that are true of it

The actual app

Screens, not mock-ups

Every picture on this site is a capture of the running app, taken by a script that fails rather than ship a blank frame. Nothing here is drawn.

The System screen with four confirmed readings — suction 130.0 psi and 55.0 °F, liquid 340.0 psi and 92.0 °F — each marked "Manual confirmed", above a System read card that says "Normal operation: superheat and subcooling are both on target with no contradicting signals." The System screen with four confirmed readings — suction 130.0 psi and 55.0 °F, liquid 340.0 psi and 92.0 °F — each marked "Manual confirmed", above a System read card that says "Normal operation: superheat and subcooling are both on target with no contradicting signals."
Readings, then the read. Superheat and subcooling graded against the target for this system.
The PT calculator on R-410A: 118 PSIG entered, a saturation temperature of 39.8 °F, and the slide-rule track with the thumb sitting between the pressure and temperature scales. The PT calculator on R-410A: 118 PSIG entered, a saturation temperature of 39.8 °F, and the slide-rule track with the thumb sitting between the pressure and temperature scales.
The pressure–temperature calculator, with the refrigerant’s own facts card.
A unit page for "RTU-1 waiting room" showing its nameplate — packaged RTU, model 48TCED12A2A5, serial 4218G30271, R-410A, TXV/EEV — and a history of two readings, each reading "Normal operation" and attributed to the technician. A unit page for "RTU-1 waiting room" showing its nameplate — packaged RTU, model 48TCED12A2A5, serial 4218G30271, R-410A, TXV/EEV — and a history of two readings, each reading "Normal operation" and attributed to the technician.
A unit in the company’s records — nameplate, photos, and the readings saved against it.
The Send report screen with the frozen homeowner document previewed under the heading "What the homeowner sees": a service report headed Northside Mechanical listing the equipment, make and model, property and address. The Send report screen with the frozen homeowner document previewed under the heading "What the homeowner sees": a service report headed Northside Mechanical listing the equipment, make and model, property and address.
The homeowner’s copy, frozen at the moment you send it.

Walk the whole job, step by step →

Where the line sits

Free is the whole diagnostic path
Measuring, grading, the differential, the pressure–temperature calculator and the reading history on that phone. No account, no card, no trial clock. The free app carries a small TunePro tips banner, and removing it is a one-time purchase. What is free and what is not →
Shared work needs an organization
Sites, equipment records, photos, crew and branded reports live in an organization’s account, which is the paid part. That is the only thing sign-in buys. See the plan →
Bring your own probes
Fieldpiece, Testo, Parker Sporlan, Yellow Jacket and NAVAC connect over Bluetooth, and every reading lands in one shared set of measurement names. Brands and instrument types →

Set up your company

Creating an organization is how sites, equipment, crew and branded reports get shared across the trucks.

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The phone app's diagnostic tools need neither of these. No account, no card, no trial clock.