Volkswagen Golf Service & Repair Manual: Refrigerant R134a

Volkswagen Golf Service & Repair Manual / Air conditioning system with refrigerant R134a / General notes on air conditioning systems / Refrigerant R134a

Air conditioners in vehicles use the evaporation and condensation process. The system contains a liquid with a low boiling point, called the refrigerant.

The refrigerant used is tetrafluoroethane R134a, which boils at -26.5°C with vapour pressure of 1 bar.

Physical data of refrigerant R134a

Chemical formula	CH2F–CF3 or CF3–CH2F
Chemical designation	Tetrafluoroethane
Boiling point at 1 bar	-26.5°C
Freezing point	-101.6°C
Critical temperature	100.6°C
Critical pressure	40.56 bar (technical) pressure equates to 39.5 bar (standard) pressure

Critical point

Critical point (critical temperature and critical pressure) means the point above which there is no longer a surface of separation between liquid and gas.

Above its critical point, a substance is always gaseous.

At temperatures below the critical point, all types of refrigerant contained within a pressure tank exhibit a liquid phase and a gas phase, so that there is a gas cushion above the liquid.

As long as there is gas in the pressure vessel alongside the liquid, the pressure depends directly on the ambient temperature → Chapter.

Note

Different types of refrigerants must not be mixed with each other. Only refrigerants specified for the respective air conditioning system may be used.

Environmental aspects of refrigerant R134a

R134a is a fluorocarbon and contains no chlorine.

R134a has a shorter atmospheric persistence than refrigerant R12.

R134a does not damage the ozone layer, the potential to reduce the amount of ozone is zero.

The Global Warming Potential (GWP) of R134a lies by approx. 1430 (the GWP for carbon dioxide lies by 1).

The contribution of R134a to the greenhouse effect is less by a factor of 10 than that of refrigerant R12.

Vapour pressure table for refrigerant R134a

The vapour pressure table for each refrigerant is published in the literature for refrigeration engineers. This table shows the vapour pressure exerted on the liquid ...

Characteristics of refrigerant R134a

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