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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 behind each one — so the call you make is one you can back up.

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The diagnostics are free and run on the phone — no account, no signal, no clock on it.

The account covers the records side: reads off the phone, reports out under your name. The diagnostics on the phone run without one.

What a conclusion looks like

A verdict with its reasons attached

This 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 — the same card as the screenshot beside it.

Each finding is graded strong, moderate or weak — the three bands the engine actually computes — so you know at a glance which one you would stake the job on.

  • Strong
  • Moderate
  • Weak

Higher up that same screen it tells you what would make the call certain: Attention — add outdoor temperature to separate a real fault from cold weather or a hot day. One more reading, and you are not guessing.

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.

The findings

Eleven faults, told apart by name

These are the cards TunePro can raise, worded the way the app words them. They arrive ranked against each other, each with the readings that put it there and the readings that argue against it.

The one that eats callbacks

Superheat is high, so you reach for the gauges and call it low on charge. TunePro checks subcooling before it agrees. Low subcooling is the sign of low charge — but subcooling running high alongside high superheat is a pattern no charge error produces, and when it sees that pair it stops talking about charge.

What it raises instead is the two causes it cannot separate from gauges alone, said out loud: a liquid-line restriction, or a metering valve underfeeding the coil. Then it hands you the test that separates them — “Feel along the liquid line with your hand or an infrared thermometer: a cold spot or frost at the filter drier means a restriction; the line staying warm until the valve itself means the valve is underfeeding.”

For the valve itself: “warm the sensing bulb in your hand — a live valve opens and superheat falls within a minute; a valve that has lost its bulb charge does not move at all.”

Tell it what is metering the coil

TXV or EEV on one setting, fixed orifice or piston on the other, and Not sure when the plate is unreadable — the choice changes how the numbers are read. On a TXV, superheat counts as a charge signal. On a fixed orifice it counts once you have entered a target, and the tolerance band widens when it is cold out. A valve overfeeding the coil is only ever called on a valve, because that is the only place it means anything.

The target it puts in front of you follows the same choice: subcooling on a valve, superheat on a fixed orifice, because that is the number carrying the charge on each.

Leave it on Not sure and it names the reading that would settle it, rather than picking for you.

It knows when these numbers stop applying

Put a heat pump in heating and TunePro tells you why, in as many words: “In heating the coils swap roles, so cooling-mode superheat and subcooling bands do not apply.” Then it points you at the work that does not depend on them — the temperature rise across the indoor coil, the defrost cycle, the outdoor coil.

Variable-capacity equipment and systems with a receiver get the same treatment, each with the reason. A modulating compressor moves superheat and subcooling as it ramps, so one steady-state reading cannot judge charge, and the app says so instead of averaging it away.

Walk the whole job, step by step →

Refrigerants

R-454B is in there, and 29 others

R-454B, R-410A, R-32, R-22, R-134a, R-407C, R-404A, R-1234yf, R-290 and the rest of a 30-refrigerant catalogue, each one carrying real properties bundled into the app rather than a table somebody typed in. It works in a crawlspace with no bars.

Blends carry their glide: where dew and bubble are more than a degree apart, the calculator shows you both instead of averaging them into one number that is wrong twice.

R-744 gets its critical point marked and its dry-ice band shaded, because below roughly 60 PSIG CO₂ does something a pressure–temperature chart cannot warn you about.

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.
R-410A at 118 PSIG.
The PT calculator on R-744 (CO₂) at 40 PSIG, reading −44.5 °F, with a warning that CO₂ forms dry ice below about 60 PSIG, a shaded dry-ice band at the bottom of the track, and the critical point marked at roughly 1055 PSIG / 87.8 °F. The PT calculator on R-744 (CO₂) at 40 PSIG, reading −44.5 °F, with a warning that CO₂ forms dry ice below about 60 PSIG, a shaded dry-ice band at the bottom of the track, and the critical point marked at roughly 1055 PSIG / 87.8 °F.
R-744, with the hazard band and the critical point.

The customer’s copy

Leave a document, not just a conversation

The outfit with the wrapped trucks leaves a printed folder. You leave a report with your company name across the top, your logo, your colour and your phone number — sent as a link from the driveway, or emailed before you have packed the gauges.

  • Yours, not ours Company name, logo, a colour and a contact block, set once and applied to every report afterwards. Our name is nowhere on it.
  • Reads as a measurement, not a pitch The readings and what they mean, and nothing else — no price, no savings claim, no prediction of how the equipment will perform later. A homeowner can carry it to somebody else for a second opinion and it still holds up, which is exactly what makes it worth handing over.
  • Hers to keep The email carries the document as a PDF attachment, and the email says so: “A PDF copy is attached to this email, which is yours to keep after the link stops working.” The private link runs ninety days and you can pull it back any time — pulling one back keeps working whatever happens to your plan.
  • Settled when you send it The document is written once and kept exactly as written. Correct a nameplate tomorrow, re-read the unit next week, change your logo next year — what you sent is what she has.
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.
Send report, with the homeowner’s copy previewed above it.

Where the reads go

Lose the phone, keep the history

A saved read attaches to the actual unit — nameplate, photos, and a history naming who took each reading and which instrument it came from. Next spring, the person standing at that rooftop unit opens what you found.

Take that read in a crawlspace with no bars and it waits in line on the phone. Readings, photos and maintenance visits queue in the order you took them, survive a reboot, and go up when signal comes back — first try or on the fourth. The screen tells you which of the two you are looking at, too: waiting for signal reads differently from waiting to retry, because only one of them is worth walking outside for.

If something does not go up, it names the reading, gives you the reason, and puts a Retry button next to it. Nothing leaves the queue without a deliberate press.

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’s record: nameplate, photos, and the reads saved against it.

Who it is for

The same product at one truck or at fifty

Two paid plans, priced per person, per month. A contractor on his own pays for one.

On your own

One truck, one login

Sign up with an email and a password, and choose Personal. Reports go out under your logo and your colour.

  • $29 a month covers you. The plan is priced per person, and one is a number of people.
  • Your reads stop living on one phone. Lose the phone, keep the history.
  • Hire somebody and invite them into the same account.

With a crew

One set of records instead of a truck park full of phones

Every technician signs in to the same sites, the same equipment records and the same customer reports. The unit somebody read in March is the unit you are standing at in July, with the nameplate photo already on it.

  • Billing is the one screen held back for owners. Anybody can look up a unit.
  • Every reading carries who took it and which instrument it came from.
  • Hire somebody and the subscription follows. Nobody buys a tier they did not need.

Free and paid

Where the line sits

Multi-Superheat for the full lineup
$9.99 USD per person, per month. Everything in Free plus the full multi-superheat lineup. Compare plans →
Free is the whole diagnostic path
Measuring, grading, the ranked findings, the pressure–temperature calculator and the reading history on that phone. It runs on the device, without an account and without signal. What is free and what is not →
Pro adds cloud records and customer reports
Readings syncing into the unit’s record, customer reports under your own branding, those reports as a PDF, and the full multi-superheat lineup. $29 USD or $39 CAD, per person, per month. See what the plan carries →
Bring your own probes
Fieldpiece, Testo, Parker Sporlan, Yellow Jacket, NAVAC, Refco and JB Industries connect over Bluetooth in the installed app, and every reading lands under one set of measurement names. Brands and instrument types →

Create your account

Sign up with an email and a password. Choose Personal or Company. You can invite people later.

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