Bar to kPa - Refrigerant Gauge Pressure Conversion

Manifold Gauges in Bar, Pressure-Temperature Charts in kPa

Refrigeration work is full of split units. The analogue manifold set hanging off the service ports is graduated in bar, the digital gauge in the toolbag may be switched to either, and the pressure-temperature data you are checking against — the manufacturer's charging table, the commissioning sheet, the fault-code appendix — is very often printed in kilopascals. Nothing about the job is difficult once the two numbers line up, which is the whole point of this pair.

The factor: 1 bar = 100 kPa exactly, so the decimal point simply moves two places. R-410A saturating at 0 °C reads 7.0 bar on the low side, which the chart writes as 700 kPa. Both figures are gauge pressure; add about 101 kPa for absolute.

Where the Two Units Meet on a Service Call

The manifold in your hand

Blue low side, red high side, both dials in bar with a saturation scale printed around the rim for one or two refrigerants — rarely the one you are working on.

The chart on the panel

Manufacturer charging tables and service manuals lean on kPa because the rest of the document is in SI, so the target pressures never match your dial's units.

Saturation is the real reading

Pressure only matters because it fixes the boiling temperature of the refrigerant. Superheat and subcooling both start with turning a pressure into that saturation figure.

The report you leave behind

Commissioning records and warranty claims usually want SI, so field readings taken in bar are written up in kPa before the paperwork goes anywhere.

Checking a Charge Against the Manufacturer's Table

On site the sequence is short, because the arithmetic itself is trivial — what matters is not mixing up which side of the system, or which unit, a number came from.

Enter what the manifold shows

Type the bar reading straight in — 7, 9.9, 23.2 — and the kilopascal value lands beside it as you type. Decimal commas are accepted, so a reading noted in a European format needs no cleaning up first.

Look the kPa value up on the chart

Read across to the saturation temperature for that refrigerant, then compare it with your line temperature to get superheat on the suction side or subcooling on the liquid side.

Copy the value into the service report

Each field carries its own copy button and hands over the number alone, with no unit or spacing to delete afterwards. Pressing Ctrl + C in a field does the same.

Reverse it for a target from the manual

The swap arrows (↔) turn the page into kPa → bar, which is what you want when the manual states a target of 1 850 kPa and you need 18.5 bar on the dial. That direction is a multiply by 0.01.

Check the reference before you trust the number: service gauges read above ambient, but thermodynamic property tables are usually absolute. A table listing 800 kPa absolute and a manifold showing 800 kPa are about 101 kPa apart, which on R-410A is worth several degrees of saturation temperature.

Refrigerant Saturation Pressures at Working Temperatures

Saturation pressures for four common refrigerants, at an evaporating condition and a summer condensing condition. Every figure is gauge pressure, which is what a manifold set actually displays.

Refrigerant	Typical duty	Saturation temp.	Gauge pressure (bar)	Gauge pressure (kPa)
R-134a	Chiller or vehicle evaporator	0 °C	1.91 bar	191 kPa
R-134a	Condensing on a hot day	40 °C	9.10 bar	910 kPa
R-404A	Medium-temperature cold room	−10 °C	3.38 bar	338 kPa
R-404A	Condensing on a hot day	40 °C	17.28 bar	1 728 kPa
R-410A	Split-system evaporator	0 °C	7.00 bar	700 kPa
R-410A	Condensing on a hot day	40 °C	23.20 bar	2 320 kPa
R-32	Split-system evaporator	0 °C	7.10 bar	710 kPa
R-32	Condensing on a hot day	40 °C	23.80 bar	2 380 kPa

Two things jump out. R-410A and R-32 sit within a few tenths of a bar of each other across the working range, while R-134a runs at roughly a quarter of their pressure at the same temperature — which is why the same manifold set and hoses are not automatically suitable for every job. Always confirm the figures against the chart for the exact refrigerant in front of you, since blends carry glide and published tables differ slightly between sources.

Handy Details for Field Work

A factor you can also do in your head

Both fields update live, and because the factor is a flat hundred the page mostly serves as a second pair of eyes on a decimal point you moved on a ladder.

Swap to chase a target pressure

Flip the direction when the manual gives kPa and you need the dial equivalent, then flip back to record what you measured.

psi and MPa are one search away

Both unit lists hold all 26 pressure units, which covers North American charts printed in psi and compressor datasheets that quote discharge pressure in MPa.

Clean figures for the job sheet

Thousands are spaced apart so 2 320 kPa stays readable, and the copy button strips the formatting back to bare digits for the report.

Charging and Diagnostic Questions

Why does R-410A sit at several times the pressure of R-134a?

Because it boils at a much lower temperature at any given pressure. At 0 °C R-134a saturates around 1.91 bar (191 kPa) while R-410A needs about 7.00 bar (700 kPa) to stay at the same temperature, and by 40 °C the gap has widened to roughly 9.1 bar against 23.2 bar. That is a property of the fluids, not a fault. It is also why R-410A equipment uses heavier tubing, higher-rated service valves and a manifold set with a suitable full-scale range.

R-32 reads almost the same as R-410A — can I share one chart?

They are genuinely close, since R-410A is roughly half R-32 by mass, and the tables sit within a few tenths of a bar over normal operating temperatures — 7.00 against 7.10 bar at 0 °C, 23.20 against 23.80 bar at 40 °C. Close is not the same as correct, though: on a fine superheat call those tenths shift the saturation temperature by around half a degree, which is a real slice of your target. Use the chart for the refrigerant on the nameplate, and remember the two are not interchangeable in a system.

Bubble point or dew point — which column applies to a blend like R-404A?

Blends change temperature as they evaporate or condense, and the chart lists both ends of that glide. The convention is dew point for suction-side superheat, because the refrigerant is fully vapour there, and bubble point for liquid-line subcooling, where it is fully liquid. R-404A is close to azeotropic so the two columns barely separate, but on a wide-glide blend picking the wrong one skews the answer by several degrees. Whatever a chart gives you, note which column you read on the service sheet.

How does a suction pressure in bar turn into superheat?

Three steps. Read the low-side pressure, convert it to the chart's units if they differ — 9.9 bar is 990 kPa — and look up the saturation temperature for that refrigerant. Then clamp a pipe probe on the suction line near the compressor and measure the actual temperature there. The difference between the measured temperature and the saturation temperature is superheat. Subcooling is the mirror image on the liquid line: saturation temperature from the high-side pressure, minus the measured line temperature.

Why is a standing vacuum test quoted in microns rather than bar or kPa?

Because the numbers that matter are far too small for a bar scale. A 500 micron target is about 0.067 kPa, or 0.00067 bar — the last thin sliver at the very bottom of a manifold's compound dial, where the needle simply cannot resolve anything useful. Micron gauges use a different sensing principle for that decade. The rise during the standing test tells you whether moisture is still boiling off or the system is leaking, and neither answer is visible on a gauge scaled for 25 bar of R-410A.

Bar to Kilopascals