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:

Changing bulbs in the front headlights (halogen H4)
Fig. 178 Rear view of the right-hand H4 headlight with plastic covers: ① dipped beam and main beam, ② turn signal and ③ side light Fig. 179 Rear view of the right-hand H4 headlight with rubber cover: ① dipped beam and main beam, ② turn signal and ③ side light First read and o ...

Switching lights on and off
Fig. 68 Next to the steering wheel: examples of the various light switches First read and observe the introductory information and safety warnings Observe any country-specific regulations when using vehicle lighting. In vehicles with a factory-fitted towing bracket, the vehicle's rear fog ...

General Information
Perform a road test to determine if a vehicle pulls to one side and if so, when and to which side. If the vehicle pulls to one side. Refer to → Chapter „Corrective Action When Vehicle Pulls to One Side“. If the vehicle ali ...