What is superheat in HVAC?

Superheat is the number of degrees above the refrigerant's saturation (boiling) point at a given pressure. It is measured at the suction line to confirm that all liquid refrigerant has evaporated before entering the compressor — protecting the compressor from liquid slugging.

What is a normal superheat reading?

For fixed-orifice (piston or cap tube) systems the target suction superheat is typically 8–12 °F measured at the evaporator outlet. TXV/EEV systems are usually set for 10–15 °F at the valve bulb. Always consult the manufacturer's specifications first — targets vary by system design.

Why is high superheat a problem?

High superheat (above ~15–20 °F) typically indicates undercharge or a restricted metering device, meaning not enough refrigerant is flowing through the evaporator. The coil is being starved, reducing cooling capacity and efficiency.

Why is low superheat a problem?

Low superheat (below ~5 °F) or negative superheat means liquid refrigerant is reaching the compressor suction. Liquid cannot be compressed and can dilute or wash the compressor oil, causing premature compressor failure.

Does this tool work for R-32 or R-454B systems?

Not yet — R-32 and R-454B are not in the current table. For those refrigerants, use a dedicated P/T chart app or the manufacturer's data sheet. The principle is identical: superheat = suction line temperature minus saturation temperature at suction pressure.

Should I measure pressure and temperature at the same location?

Yes. For accurate superheat, take the pressure reading and the temperature reading at the same physical point on the suction line — ideally at the evaporator outlet before the line runs to the condenser. Temperature drops along a warm suction line can add false superheat if you measure far from the metering device.

Superheat Calculator

Enter suction pressure and actual suction line temperature to calculate superheat for R-22, R-410A, R-404A, or R-134a systems.

Inputs

Refrigerant Type

Suction Pressure (PSIG)

Gauge pressure from manifold gauge set

Suction Line Temperature (°F)

Measured at the same point as the pressure gauge

Results

Enter pressure and temperature to see results

Pressure (PSIG)	R-410A (°F)	R-22 (°F)	R-404A (°F)	R-134a (°F)

Summary

Superheat is the difference between the actual suction line temperature and the saturation (boiling) temperature of the refrigerant at the measured suction pressure. This tool looks up the saturation temperature from built-in pressure-temperature tables for R-22, R-410A, R-404A, and R-134a, then subtracts it from the measured line temperature to give you the superheat in degrees Fahrenheit. Proper superheat — typically 8–12 °F at the evaporator outlet for fixed-orifice systems — indicates correct refrigerant charge and system health.

How it works

Select the refrigerant type your system uses (R-22, R-410A, R-404A, or R-134a).
Enter the suction pressure reading from your gauge manifold in PSIG.
Enter the actual suction line temperature measured at the same point with an electronic thermometer.
The tool looks up the saturation temperature for the refrigerant at that pressure using a built-in P/T table.
Superheat = Suction Line Temperature − Saturation Temperature.
The result is displayed with a status indicator showing whether charge is low, normal, or high based on typical field targets.

Use cases

Diagnose low refrigerant charge on a residential split system.
Verify correct charge after adding refrigerant during a service call.
Check evaporator performance — low superheat suggests a flooding evaporator, high superheat suggests starved coil.
Train HVAC technicians on pressure-temperature relationships.
Quick field calculations without carrying a P/T chart card.
Compare superheat readings before and after TXV adjustment.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu