Bentley Volkswagen.Golf.Jetta.R32.Official.Factory.Repair.Manual.1999-2005

General information for A/C system
Página 2 de 19
When water is heated in a vessel (heat absorption), water
vapor can be seen to rise. If the vapor is further heated
through heat absorption, the visible vapor turns into
invisible gas. The process is reversible. If heat is extracted
from water in gaseous form, it changes first to vapor, then
to water and finally to ice.
A - Heat absorption
B - Heat emission
Heat always flows from warmer to colder
substance
Every substance consists of a mass of moving molecules.
The fast moving molecules of a warmer substance give off
some of their energy to the cooler and thus slower
molecules. As a result, the molecular motion of the warmer
substance slows down and that of the colder substance is
accelerated. This process continues until the molecules of
both substances are moving at the same speed. They are
then at the same temperature and no further heat
exchange takes place.
Pressure and boiling point
The boiling point given in tables for a liquid is always
referenced to an atmospheric pressure of 1 bar. If the
pressure acting on a liquid changes, its boiling point also
changes.
For example, water boils at a lower temperature the lower
the pressure.
The vapor pressure curves for water and refrigerant R134a
show for example that, at constant pressure, reducing the
temperature changes vapor to liquid (in condenser) or that,
for instance, reducing pressure causes the refrigerant to
change from liquid to vapor state (evaporator).
Vapor pressure curve of water
A - liquid
B - gaseous
C - Vapor pressure curve of water
1 - Pressure acting on liquid in bar (absolute)
2 - Temperature in C
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13/2/2005