Free · Refrigerant charging
Superheat & Subcooling Calculator
Pick the refrigerant, type your gauge pressures and line temperatures, and get superheat, subcooling and a charge verdict against the target. PT charts for R-410A, R-454B, R-32, R-22 and R-134a are built in.
Suction side (superheat)
Clamp the probe 6 in. from the service valve, insulated, after 15 minutes of run time.
Liquid side (subcooling)
Metering device
Use the outdoor unit's data plate. 8–12°F is typical when it is missing.
Subcooling
9.9°F
On target
Superheat
12.4°F
Sat 39.6°F at 118 psig
Subcooling
9.9°F
Sat 99.9°F at 318 psig
Evap saturation
39.6°F
Saturated
Cond saturation
99.9°F
Saturated
R-410A pressure-temperature chart
| °F | psig |
|---|---|
| -40 | 10.8 |
| -30 | 17.8 |
| -20 | 26.3 |
| -10 | 36.5 |
| 0 | 48.4 |
| 10 | 62.4 |
| 20 | 78.7 |
| 30 | 97.4 |
| 40 | 118.8 |
| 50 | 143.1 |
| 60 | 170.7 |
| 70 | 201.7 |
| 80 | 236.5 |
| 90 | 275.3 |
| 100 | 318.5 |
| 110 | 366.5 |
| 120 | 419.5 |
| 130 | 478.0 |
| 140 | 542.6 |
| 150 | 613.9 |
Turn the repair into a signed ticket
EstimateKit builds the repair estimate on your phone, gets the customer's signature, and invoices the job when you close the panel. $49/month, 14-day free trial.
How to read superheat and subcooling
Superheat is how many degrees the suction vapor is above its saturation temperature. It tells you the evaporator is fully boiling off the refrigerant and no liquid is heading to the compressor. Subcooling is how many degrees the liquid leaving the condenser is below its saturation temperature. It tells you there is a solid column of liquid feeding the metering device.
The calculator converts gauge pressure to saturation temperature from the PT chart above, then subtracts. Fixed-orifice systems (pistons and capillary tubes) are charged to a target superheat that moves with conditions. TXV and EEV systems hold superheat on their own, so they are charged to the subcooling on the data plate.
Target superheat for fixed-orifice systems
This is the field approximation of the manufacturer's charging chart. It needs a real wet bulb reading from the return air, not a guess. When the result drops under 5°F the chart says the conditions are too cold to charge accurately; wait for a warmer day or weigh the charge in.
Before you add or remove refrigerant
- Run the system at least 15 minutes with the indoor temperature near normal.
- Confirm airflow first: clean filter, coil, blower speed and a temperature split near 18–22°F. Half of "low charge" calls are airflow.
- Take line temperatures with a clamp probe, insulated, on clean copper 6 in. from the service valve.
- Charge in small steps and let readings settle for 5–10 minutes between them.
R-454B and R-32 notes
Both are A2L refrigerants, so use A2L-rated gauges, recovery equipment and leak detectors. R-454B is a blend with about 1.5°F of glide: the calculator uses the dew point for superheat and the bubble point for subcooling, which is how the manufacturer charts are published. R-32 is a single-component refrigerant with no glide. Neither is a drop-in for R-410A.
Pricing the repair? Run the numbers through the service call pricing calculator before you write the ticket.
Frequently asked questions
What should superheat be on an R-410A system?
On a fixed-orifice system the target moves with indoor wet bulb and outdoor temperature, typically 5–25°F. On a TXV system superheat should sit around 8–14°F at the evaporator and you charge to subcooling instead. Always use the target from the manufacturer's chart or nameplate when you have it.
What is a normal subcooling reading?
Most residential TXV systems specify 8–12°F of subcooling at the outdoor unit. The exact number is on the data plate or the installation manual. Readings 3°F or more off the target usually mean the charge is off, but check for restrictions and non-condensables before adding refrigerant.
Why does the calculator say the pressure is out of range?
Each refrigerant's PT table covers a fixed range, roughly −20°F to 130°F saturation. A pressure outside that range usually means the wrong refrigerant is selected or the gauge is reading a different port. R-32 and R-454B run higher than R-410A at the same temperature; R-22 and R-134a run much lower.
Does the R-454B glide matter for charging?
Slightly. R-454B has about 1.5°F of temperature glide, so superheat uses the dew-point column and subcooling uses the bubble-point column. The calculator does that automatically when R-454B is selected. Manufacturer charging charts for R-454B are published the same way.
Can I charge by superheat on a TXV system?
No. A TXV adjusts to hold its own superheat, so superheat only tells you whether the valve is working. Charge a TXV system to the nameplate subcooling and use superheat as a check that the valve is not stuck or starved.