Refrigerant Vapor Pressure Table

WARNING: This page is about a different car, the 2022 Volkswagen ID.4 and 2021 Volkswagen ID.4. However, it is still accessible from the selected car via links, so may be relevant.

The vapor pressure table for each refrigerant is published in the literature for the refrigeration system technicians. This table makes it possible to determine the vapor pressure acting on the column of liquid in a reservoir if the temperature of the reservoir is known.
Since each refrigerant has its own specific vapor pressure table, refrigerant can be identified by measuring the pressure and temperature, for example. However, the pressure values of certain refrigerants are very similar (such as refrigerants R134a and R1234yf), and it is only possible to differentiate them via a chemical analysis. Refer to A/C TECHNOLOGY BASIC PRINCIPLES .
At absolute pressure, "0 bar (0 psi)" corresponds to absolute vacuum. Normal ambient pressure (positive pressure) corresponds to "1 bar (14.5 psi)" absolute pressure. "0 bar (0 psi)" pressure corresponds to an absolute pressure of one bar on most pressure gauges (indicated by "-1 bar (-14.5 psi)" below "0").
Pressure is measured in different units: 1 MPa (mega Pascal) corresponds to 10 bar (145.04 psi) positive pressure or 145 psi. 1 bar (14.5 psi) absolute pressure corresponds to 0 bar (0 psi) positive pressure and thus to the ambient pressure (atmospheric pressure).
Depending on the density, there is a distinct correlation between the pressure and temperature in the refrigerant circuit up to a critical temperature of 31.1 °C (88 °F). If the temperature of the refrigerant is greater than the critical temperature, then the refrigerant circuit pressure will change with the density (amount of refrigerant added).

Temperature in °C

Pressure in bar (positive pressure) of R744 depending on density in kg/m⁽¹⁾

200 kg (440.92 lbs)/m⁽¹⁾

225 kg (496.04 lbs)/m⁽¹⁾

250 kg (551.16 lbs)/m⁽¹⁾

300 kg (661.39 lbs)/m⁽¹⁾

-10

-5

31.1 (critical temperature)

102

100

111

102

108

121

107

116

130

⁽¹⁾

The density specifies how many kilograms of refrigerant R744 per m of available internal refrigerant circuit volume are added. The capacity for refrigerant R744 was calculated for a particular available internal refrigerant circuit volume. For example, if there is too much refrigerant oil in the refrigerant circuit, the available internal volume is reduced and the refrigerant circuit may be overfilled, even though the added amount of refrigerant is OK.

⁽²⁾	A density of approximately 250 kg (551.16 lbs)/m of available internal volume is designed for the refrigerant circuit in vehicles.

⁽³⁾

If the density is exceeded, the static pressure in the refrigerant circuit increases sharply and the pressure relief valve on the low-pressure side activates (at a density of 400 kg (881.85 lbs)/m , for example, the static pressure will already start to increase to 144 bar (2, 088.55 psi) at an ambient temperature of 80 °C (176 °F)).

To protect the components belonging to the refrigerant circuit, the A/C system is no longer switched on (the A/C compressor is no longer activated) when the static pressure (pressure before first activating) in the refrigerant circuit is less than 30 bar (435.11 psi) (due to underfilling) at an ambient temperature greater than 0 °C (32 °F) or greater than 95 bar (1, 377.86 psi) regardless of the ambient temperature (for example, in a paint shop drying oven or because of a too high of density).