Volkswagen Polo Service & Repair Manual: Critical Point

Volkswagen Polo Service & Repair Manual / Refrrigerant R134a Servicing / A/C System, General Information / Refrigerant R134a / Critical Point

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 → 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.

Refrigerant R134a Physical Data

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 ref ...

Refrigerant R134a Environmental Information

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 ref ...

Other materials:

Introduction
This chapter contains information on the following subjects: → Warning and indicator lamps → Handbrake → Parking → Information on the brakes → Brake support systems → Switching the TCS on and off → Brake flu ...

Replacing the battery
Fig. 21 Vehicle key: opening the battery case cover Fig. 22 Vehicle key: removing the battery First read and observe the introductory information and safety warnings Volkswagen recommends having the battery changed at a Volkswagen dealership or by a qualified workshop. The battery is l ...

Information stored in the control units
First read and observe the introductory information and safety warningsYour vehicle is factory fitted with electronic control units which are responsible for engine and gearbox management. The control units also monitor the function of the exhaust system and the airbags. These electronic con ...