Volkswagen Golf Service & Repair Manual: 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. |
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| Physical data of refrigerant R134a |
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| 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 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. |
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| 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. |
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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 ...
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Vapour pressure table for refrigerant R134a