Critical Point

WARNING: This page is about a different car, the 2016 Volkswagen Beetle, 2015 Volkswagen Beetle, 2014 Volkswagen Beetle, and 2013 Volkswagen Beetle. However, it is still accessible from the selected car via links, so may be relevant.

Vehicle air conditioning systems make use of the vaporization and condensation process. In this case, one works with a substance which boils easily, designated as refrigerant.

The refrigerant employed is tetrafluoroethane R134a, which boils at -26.5 °C (-15.7 °F) at a vapor pressure of 1 bar (14.5 psi).

The critical point (critical temperature and critical pressure) is that above which there is no longer a boundary between liquid and gas.

A substance above its critical point is always in the gaseous state.

At temperatures below the critical point, all types of refrigerant in pressure vessels exhibit both a liquid and a gas phase, i.e. there is a layer of gas above the liquid.

As long as there is still gas present in the container next to the fluid, pressure is dependent on ambient temperature, refer to REFRIGERANT R134A VAPOR PRESSURE TABLE .

NOTE:

Different types of refrigerant are never to be mixed. Only the refrigerant designated for the corresponding A/C system may be used.