What Pressure Should R-454C Be?
Updated October 20, 2026
R-454C A2L Lower toxicity, lower flammability
You are on an R-454C system — a low-GWP A2L blend now going into new commercial refrigeration — with gauges connected and a big gap between the two saturation temperatures on the dial. That gap is the glide, and it is large.
Read superheat off the wrong curve on a blend that glides this much and you can be off by more than ten degrees — enough to flood or starve the evaporator while the gauge looks fine.
This page gives R-454C suction by application at the AHRI walk-in coil temperatures, head pressure by outdoor temperature, and the wide dew-to-bubble standing range.
R-454C suction is about 5.7–8.8 psig at a −20°F freezer coil and 40–46 psig at a 25°F cooler coil, with head around 239–311 psig at 95°F outdoors. It is a high-glide, low-GWP A2L blend, so read suction on the dew curve and treat standing pressure as a wide dew-to-bubble range.
R-454C pressures for walk-in coolers and freezers
Suction is set by the evaporator coil temperature. The AHRI 1250-2020 walk-in rating points — a 25°F cooler coil and a −20°F freezer coil — give the two suction bands you check most. Read suction on the dew curve.
| Application | Suction (psig / kPa) |
|---|---|
| Walk-in cooler (25°F coil) | 40–46 psig 273–319 kPa |
| Walk-in freezer (−20°F coil) | 5.7–8.8 psig 39–61 kPa |
Head pressure by outdoor temperature
Head is set by the condenser and climbs with the outdoor air, the same on a cooler or a freezer. Find your outdoor temperature down the left column.
| Outdoor | Head (psig / kPa) |
|---|---|
| 65°F 18.3°C | 153–207 psig 1,055–1,429 kPa |
| 70°F 21.1°C | 166–223 psig 1,142–1,534 kPa |
| 75°F 23.9°C | 179–239 psig 1,232–1,645 kPa |
| 80°F 26.7°C | 193–255 psig 1,328–1,761 kPa |
| 85°F 29.4°C | 207–273 psig 1,429–1,883 kPa |
| 90°F 32.2°C | 223–292 psig 1,534–2,010 kPa |
| 95°F 35.0°C | 239–311 psig 1,645–2,143 kPa |
| 100°F 37.8°C | 255–331 psig 1,761–2,282 kPa |
| 105°F 40.6°C | 273–352 psig 1,883–2,427 kPa |
| 110°F 43.3°C | 292–374 psig 2,010–2,578 kPa |
| 115°F 46.1°C | 311–397 psig 2,143–2,736 kPa |
Reading gauges on a high-glide blend
R-454C evaporates and condenses across a wide temperature range, so every pressure has a lower dew temperature and a much higher bubble temperature. Use the dew curve for suction and(/superheat-calculator/); use the bubble curve for the liquid line and(/subcooling-calculator/). Because the glide is large, an A2L-rated manifold that shows both scales — or a calculator that does the lookup — saves you from reading the glide as superheat.
Standing pressure: a wide dew-to-bubble range
Once the system has been off long enough for the pressures to equalize, R-454C reads across a wide dew-to-bubble band at the temperature of the coolest part of the system (indoor or outdoor) — for example 108–137 psig at 68°F (20°C). Treat standing pressure as a range, not a single number; the spread is the glide.
| Off temperature | Standing (dew–bubble, psig / kPa) |
|---|---|
| 65°F 18.3°C | 102–130 psig 706–896 kPa |
| 70°F 21.1°C | 112–141 psig 773–973 kPa |
| 75°F 23.9°C | 123–153 psig 845–1,055 kPa |
| 80°F 26.7°C | 134–166 psig 922–1,142 kPa |
| 85°F 29.4°C | 145–179 psig 1,003–1,232 kPa |
| 90°F 32.2°C | 158–193 psig 1,089–1,328 kPa |
| 95°F 35.0°C | 171–207 psig 1,180–1,429 kPa |
| 100°F 37.8°C | 185–223 psig 1,277–1,534 kPa |
| 105°F 40.6°C | 200–239 psig 1,378–1,645 kPa |
| 110°F 43.3°C | 216–255 psig 1,486–1,761 kPa |
| 115°F 46.1°C | 232–273 psig 1,599–1,883 kPa |
When R-454C readings are off
These are refrigeration faults; match a suspect reading to the pattern below, reading suction on the dew curve, then confirm with a calculator before adding refrigerant.
A healthy R-454C system at 95°F outdoors reads about 40–46 psig suction on a 25°F cooler coil, 5.7–8.8 psig on a −20°F freezer coil, and 239–311 psig head.
| Fault | Suction | Head | Superheat | Subcooling | First thing to check |
|---|---|---|---|---|---|
| Likely undercharge | low | low | high | low | Find and fix the leak, then recharge by weight |
| Likely overcharge | high | high | low | high | Verify condenser airflow, then recover to target |
| Likely restriction | low | normal–low | high | high | Look for a temperature drop across the filter-drier or liquid line, then check the metering device. |
| Likely metering device overfeeding | high | low | low | low | A TXV or EEV stuck open or with a loose sensing bulb; on a fixed-orifice system, the piston size. |
Confirm a reading before adjusting the charge: the pressure diagnostic tool, low suction pressure and high head pressure guides walk a reading to its cause.
Frequently asked questions
What pressures does R-454C run at in a walk-in freezer?
About 5.7–8.8 psig suction at the AHRI −20°F freezer coil temperature, read on the dew curve, with head near 239–311 psig at 95°F outdoors. Suction is set by the box, not the weather: it runs higher while a warm box pulls down and settles into this band once the box is at temperature. A reading well below it on a cold box points to an undercharge, a restriction, or a coil needing defrost.
What is R-454C standing pressure?
A range, not one number — once the pressures have equalized, R-454C reads across its dew-to-bubble band, about 108–137 psig at 68°F (20°C). The standing-pressure table above gives the band from 65 to 115°F. The wide spread is R-454C's glide.
What is R-454C saturation pressure at 20°C (68°F)?
About 108–137 psig at 68°F (20°C), given as a dew-to-bubble range because R-454C glides. The lower (dew) end is the saturated-vapor pressure; the higher (bubble) end is the saturated-liquid pressure. Use the dew end when comparing to a suction reading.
What is R-454C discharge pressure?
About 239–311 psig at 95°F outdoors, rising on hotter days because the condensing temperature sits above the outdoor air. Head is set by the condenser and ambient, not the box, so it is the same on a cooler or a freezer. Read the head chart above for your outdoor temperature.
How these numbers are calculated
Every pressure here is R-454C's saturation pressure at the stated temperature, calculated with CoolProp 7.2.0. Suction (low side) uses the saturated-vapor (dew) pressure; head (high side) uses the saturated-liquid (bubble) pressure.
Suction uses the AHRI 1250-2020 walk-in coil temperatures — 25°F for a cooler, −20°F for a freezer — read on the dew curve at the coil ±3°F; head is a condenser running 10–30°F above the outdoor air. We use 95°F as the reference because it is one of the AHRI 1250 outdoor rating temperatures for condensing units.
Sources: CoolProp 7.2.0; AHRI 1250-2020 (walk-in ratings). Your equipment maker's charging chart or the unit data plate overrides these reference values for that specific system.