HVAC Calculator

Subcooling Calculator

Subcooling from the liquid-line pressure and temperature, judged against the TXV target, so you know whether the charge is low, right, or high.

Field brief

Subcoolingsaturated liquid temp − liquid-line temp, measured at the liquid line near the condenser outlet.8–14°F TXV

Why it matterson a TXV it is the primary charging check: low means low charge, high means overcharge.TXV charges by SC

Read itenter the liquid-line pressure and temperature; the tool does the PT conversion.R-410A · R-454B · R-32 +

Intry VerifiedA worked default reading, traceable end to end: what it was calculated from, what it was run with, how it was checked, and who has final say.

Superheat in band, charge not assessed12°F superheat, 11°F subcooling

Where this number comes fromIntry Verified

Calculated from

R-410A PT chart, TXV. Method routed from the manufacturer service literature for the unit you name; bands from CEC RA3 Table RA3.2-1 (Installer at final) with the target from RA3.2-2 or the equipment nameplate; airflow precondition from CEC-400-2022-010-AP JA6.1.6.3 (2022 edition; JA6.1 is RESERVED in the 2025 edition); dose from York ST-022-12; hazard instructions from Rheem RD16AY 5.7 and Lennox 13ACX 506374-01. See the full receipt ↓

Run with

RefrigerantR-410A
MeteringTXV
Suction118 psig, 52°F
Liquid350 psig, 96°F

Checked

Every figure an Intry calculator computes comes from a locked source module, not hand-typed. 27820 automated checks re-derive and source-check the numbers against the locked modules each figure is traced to: the manufacturer PT tables behind the saturation temperatures, superheat and subcooling, and the transcribed code and service-literature constants behind the charge, metering, airflow, approach and discharge line figures, each quoted with its own source in the panel it appears in before each deploy. This is our own deterministic gate, not a third-party audit.

Final say

The unit nameplate and the manufacturer's charging chart have final say.

What Intry Verified means

Intry Verified · Build 066369F · 2026-09-07

Target Subcooling by Refrigerant

Typical subcooling targets (°F) by refrigerant and metering device. Always verify against the equipment nameplate.
Refrigerant	Type	TXV subcooling	Fixed-orifice subcooling
R-410A	HFC	8–14°F	4–10°F
R-454B	A2L	8–14°F	4–10°F
R-32	A2L	8–14°F	4–10°F
R-22	HCFC	8–14°F	4–12°F
R-134a	HFC	8–14°F	4–10°F
R-407C	HFC	8–14°F	4–10°F

The target ranges in the table above and every pressure-temperature value this tool reads are derived from the same locked refrigerant module the superheat and subcooling hub uses, and re-checked on every build: a value that no longer matches its source fails the build.

How to Measure Subcooling

Attach a refrigerant gauge to the liquid service valve (or the liquid-line access port) and read the liquid-line pressure in psig.
Convert that pressure to its saturation (condensing) temperature with the PT chart for your refrigerant. On a zeotropic blend, use the bubble point, not the dew point: a blend boils and condenses across a range rather than at one temperature, and the liquid line is at the bubble end. That covers R-407C, R-454B, R-407A, R-448A, R-449A, so it includes R-454B, the refrigerant most new residential equipment now ships with. The calculator above does this conversion for you and picks the right column per refrigerant.
Clamp a pipe thermometer to the liquid line near the condenser outlet and read the actual line temperature.
Subtract: subcooling = saturated liquid temperature − measured liquid temperature. The liquid is cooler than its saturation point, so saturation comes first.
Compare the result to the target for your refrigerant and metering device, and read it beside superheat before you add or recover charge.

Why Is My Subcooling High or Low?

Subcooling tells you how much liquid is stacked in the condenser, but it only names a cause when you read it beside superheat. Two readings, four outcomes:

High subcooling

Above the target range, the condenser is holding too much liquid. The usual cause is an overcharge, and the tell is low superheat beside it: excess refrigerant floods the condenser and pushes liquid toward the evaporator outlet. Before you recover, rule out low or restricted condenser airflow, which backs liquid up the same way. If superheat is high while subcooling is high, that is not an overcharge, it is a liquid-line or metering-device restriction trapping refrigerant on the high side. Recover charge only once airflow and restriction are cleared.

Low subcooling

Below the target range, the condenser does not have enough liquid stacked to subcool it. Read superheat first: high superheat with low subcooling is the classic undercharge, so find and fix the leak before adding refrigerant, since a system that lost charge lost it to a leak. Low superheat with low subcooling is not a charge problem at all, it points to a weak compressor or an overfeeding TXV. Adding refrigerant to a low-subcooling system without reading superheat is the most common way a good tech overcharges a system with a hidden restriction.

Your Nameplate Target Beats the Generic Range

The 8 to 14 degree F range above is a field envelope, not a specification. When the equipment prints its own target subcooling, that number governs, the same way the manufacturer’s instructions outrank a generic rule anywhere else in the trade. Enter it in the calculator and the tool grades against your figure instead of the envelope.

Most nameplates print a target and no tolerance, which leaves an obvious question: how far off is off? Where the literature prints a tolerance, enter it and the tool uses it. Where it does not, the tool bands your target by ±3°F and says so on screen, because that is the figure California’s Reference Appendices publish for exactly this comparison: Table RA3.2-1, Standard Charge Verification, variable metering, Installer Testing at Final, reads “Subcooling tolerance ±3°F of the manufacturer-specified target”. It is the code’s band around the manufacturer’s number, not ours, and the calculator labels it as the code’s wherever it uses it.

Where there is no nameplate target at all, the tool publishes no band of its own for it and falls back to the field envelope. The same appendix declines to supply a target when the manufacturer has not, and inventing one would be a pass or fail line wearing an authority nothing gave it.

When Subcooling Does Not Indicate Charge

Subcooling is a charge indicator because a correctly charged condenser stacks a predictable amount of liquid. A system with a liquid receiver breaks that link on purpose: the receiver holds a reservoir of liquid and feeds the metering device a full column whether the system is slightly over or slightly under. Subcooling at the receiver outlet then reports the receiver, not the charge, and it can read perfectly normal on a system that is measurably low.

This is common on commercial refrigeration and rare on residential split systems, which is why the range table above is honest for most of the traffic that reaches this page and wrong for some of it. The calculator asks which you have. Tell it there is a receiver and it stops grading subcooling as a charge number and says why, rather than printing a pass or fail against a target that cannot mean what it looks like it means. On those systems the charge is set by weight or by the manufacturer’s own procedure, not by the number this page is about.

01At
altitude

Above sea level, subcooling reads high

A manifold gauge reads pressure above the local atmosphere, and every PT chart, ours and the manufacturer’s, is built for sea level. Higher up the real saturation temperature is lower than the chart says, so measured subcooling displays high. That is the overcharge signature this page just told you to read, which means at elevation the pull is toward recovering refrigerant that should stay in the system. The size is modest and worth knowing exactly: on R-410A it is about 0.5°F of subcooling at 5,000 ft and about 0.9°F at 10,000 ft, with R-454B a shade larger at 0.6°F and 1.0°F. Against a ±3°F band that is a fraction of the window rather than a verdict, but it runs one way, and one way is what turns a borderline reading into a decision.

This calculator does not correct for it, on purpose. No manufacturer instructs an altitude correction for charging, so a corrected reading would disagree with the gauge, the chart and the manual in your hand with nothing telling you why. Know the bias and its direction instead: at elevation treat a slightly high subcooling as expected rather than as a reason to recover, and weigh in to the nameplate when the manufacturer says to.

Charge by Subcooling, or by Superheat?

The metering device decides which reading is your primary charging indicator. A TXV is charged by subcooling. The valve actively holds superheat steady, so adding or removing charge barely moves superheat and shows up in the condenser as subcooling instead. Weigh in to the manufacturer subcooling target, commonly 8 to 14 degrees F on a modern residential TXV. A fixed orifice or piston is charged by superheat, compared to a manufacturer charging-chart target set by indoor wet-bulb and outdoor dry-bulb. Most modern residential equipment uses a TXV, so subcooling is usually your number, but always confirm the metering device on the coil before you trust either reading.

Charging a fixed-orifice system, or want superheat and subcooling read together? Use the full superheat & subcooling calculator for the four-quadrant diagnosis and the fixed-orifice target-superheat method.

02Source
receipt

The documents this charging engine reads

The charging method this tool routes you to, the pass and fail bands it applies, the airflow precondition it checks first, the dose the protocol loop gives you, and the hazards it refuses to charge through are each computed by a locked engine from the documents below. The pressure-temperature conversion behind the raw superheat and subcooling numbers has its own receipt on this page and is not repeated here.

CEC-400-2022-010-AP, Reference Appendix RA3 Table RA3.2-1 (Installer Testing at Final): The pass and fail bands, and the conditions they hold under. Variable metering devices are judged on subcooling to plus or minus 3 degrees F of the manufacturer-specified target; fixed orifices on superheat to plus or minus 5 degrees F of the target for the conditions; the metering device itself against the manufacturer's specification or 4 to 25 degrees F. The same table states the envelope those tolerances hold inside, and the engine checks it before applying any of them: outdoor dry-bulb 55 to 115 degrees F on a fixed orifice and 55 to 120 on a variable metering device, with return-air dry-bulb at or above 70. The Installer row is the one shipped, never the looser ECC and HERS Rater row beside it.
CEC-400-2022-010-AP, Reference Appendix RA3 Table RA3.2-2 (target superheat): The target superheat grid for fixed-orifice charging, indexed by indoor wet-bulb and outdoor dry-bulb. Cells are machine-parsed from the appendix rather than transcribed by hand, and a sample was compared against a manufacturer grid from a different publisher as an outside check. The comparison is disclosed rather than claimed as proof: two publishers printing the same targets can inherit one lineage.
CEC-400-2022-010-AP, Joint Appendix JA6.1.6.3 (the airflow precondition): Why this tool checks airflow before it grades a charge, and why it will refuse to grade one. Items 1 to 3 each require that the minimum airflow requirement from item 4 is satisfied before their charge criteria are valid, so a superheat or subcooling reading taken on restricted airflow is not a charge measurement. The direction depends on the metering device: on a fixed orifice a starved evaporator drives superheat DOWN and widens the temperature split, which reads like an overcharge, while on a TXV the valve holds superheat and the fault shows in suction pressure and subcooling. That is the confound the whole air-side check exists to separate.
Carrier PH5SAN5, Carrier SM10-R454B-03, Carrier 25SCA5, Goodman IOG-4048C, ICP 428 01 5106 00, Trane 88-M5MHWUN-1A-EN, Rheem RD16AY, and Bosch service literature: Which charging method a given machine actually permits, and when the manufacturer says not to check the charge at all. Carrier PH5SAN5 (R-454B installation instructions) states the outdoor window it publishes for checking charge and states the airflow precondition directly; Trane and Bosch reach the same place in their own words. Carrier SM10-R454B-03 supplies the sentence defining what a dashed cell on a superheat grid means, which is an instruction not to charge on that reading. Goodman IOG-4048C and the ICP grid (428 01 5106 00) supply the dashed regions themselves. Trane 88-M5MHWUN-1A-EN is the ductless installer guide behind the mini-split fork: it publishes no superheat or subcooling procedure at all, which is why this tool declines to issue a reading-based charge verdict on ductless equipment, and we state that as evidence about THAT guide rather than about every ductless machine. Rheem RD16AY supplies the evaporator-icing instruction the engine will not charge through. Where these documents route the technician to a weigh-in or to the unit’s own charging procedure, this tool routes there too instead of grading a reading the manufacturer does not charge from.
The per-machine charge-target corpus (registered manufacturer books, cited by form number): Where a specific machine's target subcooling is written, quoted from that manufacturer's own book with its form number. 15 documents across 7 brand families are registered and content-pinned: Carrier (SM10-R454B); Goodman (IOD-4064A, IOG-4048C, IOG-4064A); York (5391577-UIM-B-0718, 6411591-UIM-B-0824, 6694740-UIM-B-1025); Lennox (100108); Nortek (708921E, 7094080); Rheem (92-104921-25-04, 92-110354-01-01); Trane (11-AC22D1-1, 18-AC94D1-4-EN, 4TWX6060E-SF-1A). The tool publishes NO target subcooling value of its own from any of them. What it publishes is WHERE the figure lives on that machine, what that manufacturer calls it, the verbatim sentence it is read from, and which model series that sentence covers - so a claim read out of one book stops at the machines that book's own cover names. Where a book's current revision cannot be established, or where its own pages disagree, the value stays withheld and the reason is printed instead.
York ST-022-12, Figures 1 and 2 (example charging charts): The dose and the wait in the protocol loop: add or remove charge in one-ounce increments and let the system stabilize for ten minutes, repeating until the reading is in band. York prints these as examples and says so, and the tool passes that scope through rather than presenting the increment as a universal specification.
Rheem RD16AY / RD18AY section 5.7, and Lennox 13ACX 506374-01 page 20: The two hazards this engine will not charge through. Rheem's instruction covers running a system at a suction pressure that will ice the evaporator coil, and it is quoted with its own scope, which names cooling mode. Lennox states the low-superheat floor below which refrigerant must not be added, because liquid reaching the compressor is damage happening in that instant rather than a charge level. Both are carried on every branch, including the branches where a charging instruction is being withheld.
Copeland discharge-temperature guidance, and Proctor Engineering on airflow and capacity: The two checks that sit beside the charge rather than inside it. Copeland's discharge-line temperature limit is what the tool watches for a compressor running hot. Proctor's finding that a passing temperature split can also mean low airflow AND low capacity together is why a passing split is not treated as proof the air side is healthy.

This receipt binds the documents the CHARGING engine consumes. It is not a claim that every sentence around the result is drawn from them, and it is not a substitute for the equipment's own instructions: where a nameplate or a service manual states a target, a tolerance or a procedure, that document governs and this tool says so. The California criteria are a state compliance standard, applied here because they are published, specific and checkable, not because they are the only correct way to charge a system. Where no primary publishes a band, this tool publishes none.

Run this in your AI. Ask Claude or ChatGPT to check the subcooling and whether the charge is right from your liquid-line pressure and temperature and it runs the Intry Superheat & Subcooling Calculator live, handing back the verdict with its cited source instead of a guess. Then keep the reading as one job in the Intry app.

Subcooling FAQs

How do you calculate subcooling?

Subcooling is the gap between the saturation temperature at your liquid-line pressure and the actual liquid-line temperature, so it takes two readings and one conversion. Read the liquid-line pressure at the service valve, let the calculator above turn it into a saturation (condensing) temperature for your refrigerant, clamp a thermometer to the liquid line near the condenser outlet, and subtract the measured temperature from the saturation temperature. The tool does the pressure-to-temperature step for every refrigerant it supports, including the bubble-point handling a zeotropic blend needs.

What is a good subcooling?

On a TXV system the common target is 8 to 14 degrees F, and the table above lists the range for each refrigerant. The number that actually governs the job is the one on the equipment nameplate, and it always wins over a generic range. Subcooling is the primary charging check on a TXV because the valve holds superheat steady, so charge level shows up in the condenser as subcooling rather than at the suction line.

Is 16 degrees of subcooling too high?

On most TXV systems, yes: it sits above the usual 8 to 14 degrees F range and points toward an overcharge. Before you recover any refrigerant, rule out low or dirty condenser airflow, which stacks liquid in the condenser and inflates subcooling the same way a real overcharge does. If the airflow is fine, recover in small steps and recheck subcooling and superheat together against the nameplate target before you decide you are done.

What does low subcooling mean?

Low subcooling means the condenser is not holding enough liquid, and the reading next to it tells you why. If superheat is high alongside it, the system is low on charge, so find and repair the leak before adding refrigerant. If superheat is also low, the charge is not the problem and you are looking at a weak compressor or a TXV that is overfeeding. A liquid-line restriction raises subcooling rather than lowering it, so it is never behind a low reading.

Do you charge by superheat or subcooling?

The metering device decides. A thermostatic expansion valve holds superheat steady, so you charge it by subcooling and weigh in to the nameplate target. A fixed orifice or piston has no such regulation, so you charge it by superheat against the manufacturer charging chart set by indoor wet-bulb and outdoor dry-bulb. Identify the device on the coil first, then read both numbers together before you add or recover anything.

Where do you measure subcooling?

At the liquid line, the warm high-pressure line running from the condenser outlet to the metering device. Put a gauge on the liquid service valve for the pressure, convert it to a saturation temperature, and clamp a pipe thermometer on the liquid line close to the condenser outlet for the actual temperature. Subcooling is that saturation temperature minus the measured temperature.

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