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:

A/C Pressure/Temperature Sensor -G395
Note For switching pressures, removing and installing switches and switch arrangement and version, see vehicle-specific refrigerant circuit. Refer to → Rep. Gr.87. ...

Seat belt protection
Fig. 49 Driver restrained by a properly positioned seat belt during a sudden braking manoeuvre First read and observe the introductory information and safety warnings Correctly fastened seat belts can make a major difference. When fastened properly, seat belts hold the vehicle occupants in ...

Single Wire Seals, Installing
Note Single wire seals prevent the penetration of water and dirt into the contact housing. They are installed, for example, in the engine compartment and must be reinstalled after a repair. Single wire seal is crimpe ...