Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...
Air conditioner with refrigerant R134a - Edition 11.2018
⇒ “1 Warning instructions when working on vehicles with high-
voltage system”, page 1 .
2.5
Principles of air conditioning systems
⇒ “2.5.1 Physical principles”, page 7
⇒ “2.5.2 Pressure and boiling point”, page 7
⇒ “2.5.3 Vapour pressure table for refrigerant R134a”,
page 8
⇒ “2.7 Properties of refrigerant R134a”, page 11
2.5.1
Physical principles
The four familiar states of water apply to air conditioning refriger‐
ants, too.
1 - Gas (invisible)
2 - Vapour
3 - Liquid
4 - Solid
When water is heated in a vessel (heat absorption), water vapour
can be seen to rise. If the vapour is further heated through heat
absorption, the visible vapour turns into invisible gas. The process
is reversible. If heat is extracted from gaseous water -A-, it
changes first to vapour -B-, then to water and finally to ice.
A - Heat absorption
B - Heat emission
Heat always flows from a warmer to a 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 contin‐
ues until the molecules of both substances are moving at the
same speed. They are then at the same temperature and no fur‐
ther heat exchange takes place.
2.5.2
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.
2. General information on air conditioning systems
7
English 
