HVAC Calculator
Subcooling Calculator
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.
Where this number comes fromIntry Verified
- Calculated from
- R-410A PT chart, TXV
- 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. 9547 automated checks re-derive and source-check the numbers against the manufacturer PT chart it came from 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.
Intry Verified · Build F65C2F9 · 2026-07-24
Target Subcooling by Refrigerant
| 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 | 10–16°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 such as R-407C, use the bubble point. The calculator above does this conversion for you.
- 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.
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.
superheat_subcooling tool 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.
Related Calculators
Superheat & Subcooling Calculator
The full charge check: superheat and subcooling read together with the four-quadrant diagnostic, 10 refrigerants, and the fixed-orifice target-superheat method.
Subcooling on a Heat Pump
A heat pump charges like an AC in cooling mode, but the reversing valve changes the rules in heating. Where to measure and when to weigh it in.
A2L Charge Limit Calculator
Maximum R-454B and R-32 charge for a room, or minimum room area for a charge, per UL 60335-2-40 and ASHRAE 15.2. Know the limit before you set the charge.
A2L Line Set Calculator
Before you charge, size the line set and check whether an existing R-410A set can be reused with R-454B. REUSE, FLUSH, or REPLACE verdict with the charge adjustment.
Subcooling is dialed in. Was the system sized right to begin with?
Chronic charge problems on a short-cycling unit often trace back to oversizing. The BTU calculator runs the load by climate zone, insulation, and windows so you can check the tonnage against the house, not the nameplate.