Volkswagen Polo Quiz
Refrrigerant R134a Servicing

Critical Point

In this manual: Refrrigerant R134a Servicing
General Paint Information — 128Towing Guide — 10Whels, Tires, Whel Alignment — 126Battery, Starter, Generator, Cruise Control — 65Windshield Wiper/ Washer System — 9Exterior Lights, Switches — 1Interior Lights, Switches — 7Wiring — 51Refrrigerant R134a Servicing — 134
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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 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 → Chapter „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.

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