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:

Welding and Soldering on Refrigeration Systems
Before performing welding or soldering work on vehicles near the air conditioning system components, extract the refrigerant and remove the residue by flushing with compressed air and nitrogen. The products of refrigerant decomposition d ...

Changing gear using Tiptronic
Fig. 113 Selector lever in Tiptronic position (left-hand drive) The controls are mirrored for right-hand drive vehicles Fig. 114 Steering wheel with paddles for Tiptronic First read and observe the introductory information and safety warnings Using Tiptronic, the gears can be shifted u ...

Underseal
First read and observe the introductory information and safety warningsThe underside of the vehicle is coated to protect it from corrosion and damage. The protective coating on the underside of the vehicle could be damaged when driving. Volkswagen therefore recommends that the protective coati ...