R-454B PT Chart (Pressure-Temperature)

How do you read an R-454B PT chart?

Find the temperature in the left column, then read across. The bubble (liquid) column is the pressure where liquid R-454B starts to boil. The dew (vapor) column is the pressure where the last drop has boiled off. For a single-component refrigerant like R-32 or R-22 those are the same number. For R-454B they differ by several psi, so you have to pick the right column for the side of the system you're measuring.

1. 1

   Suction side: use dew.

   Read suction pressure at the service valve, look up the dew (vapor) saturation temperature, and subtract it from the suction line temperature. That's superheat.

2. 2

   Liquid side: use bubble.

   Read liquid line pressure, look up the bubble (liquid) saturation temperature, and subtract the liquid line temperature from it. That's subcooling.

3. 3

   Compare with the target.

   The target superheat or subcooling comes from the unit's charging chart or nameplate, not from the PT chart. Fixed-orifice systems usually charge by superheat and TXV/EEV systems by subcooling, but follow the manufacturer.

What is temperature glide in R-454B?

Glide is the temperature difference between the bubble point and the dew point at one pressure. R-454B's two components boil at different temperatures, so as it evaporates the remaining liquid gets richer in the less volatile one and the boiling temperature climbs. In this table that works out to about 2.7°F at 110 psig and 2.6°F at 330 psig. For example, at 118.3 psig the dew point is 45.0°F and the bubble point is 42.3°F.

In pressure terms the gap is larger: at 100°F the bubble pressure is 303.3 psig and the dew pressure is 291.9 psig. Reading the wrong column overstates or understates superheat and subcooling by roughly the glide, which is enough to push a charge decision the wrong way. Because the blend can fractionate, charge it as liquid unless the manufacturer says otherwise.

Is R-454B flammable? A2L safety notes

R-454B carries the ASHRAE safety classification A2L: lower toxicity (A) and lower flammability (2L). Under ASHRAE Standard 34, a 2L refrigerant has a maximum burning velocity of 10 cm/s or less when tested at 23°C and 101.3 kPa. 2L is the lowest flammability class above nonflammable (class 1), but a 2L refrigerant can still burn.

• EPA lists R-454B as acceptable with use conditions for new residential and light commercial air conditioning and heat pumps, with a GWP of 470 (EPA SNAP). The use conditions are in the May 6, 2021 rule.
• Per EPA SNAP approvals, A2L refrigerants go in new equipment designed for them only. Don't retrofit R-454B into an R-410A system and never mix refrigerants (Daikin A2L PT chart).
• Use recovery equipment, cylinders and leak detectors rated for A2L refrigerants, keep ignition sources away from the work area, and ventilate before brazing.
• The equipment manufacturer's installation instructions and your local code set the rules for leak detection, charge limits and labeling on a given unit.

Where these numbers come from

We compute the table ourselves with CoolProp 8.0.0, an open-source thermophysical property library, using its Helmholtz-energy equations of state for an R-32/R-1234yf mixture at the ASHRAE 34 composition (68.9/31.1% by mass). Pressures are gauge (psig), relative to a standard atmosphere of 14.696 psia; at altitude your gauge reads differently for the same saturation temperature.