A/C System Principles - Audi 100 1991 Repair Manual

Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A2 2001 ➤ , A ...
Refrigerant R134a Servicing - Edition 01.2011
1.3

A/C System Principles

⇒ "1.3.1 Physical Principles", page 18
⇒ "1.3.2 Pressure and Boiling Point", page 18
⇒ "1.3.3 Comfort", page 19
⇒ "1.3.4 A/C System Operation", page 20
1.3.1 Physical Principles
The four known states of water also apply to air conditioning sys‐
tem refrigerants.
1 - Gaseous (invisible)
2 - Vapor
3 - Liquid
4 - Solid
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 -A-,
it changes first to vapor -B-, then to water and finally to ice.
A - Heat absorption
B - Heat emission
Heat Transfer
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.
1.3.2 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
fluid changes, its boiling point also changes.
Note
Pressure is measured in different units: 1 MPa (mega Pascal)
corresponds to 10 bar positive pressure or 145 psi, 1 bar absolute
pressure corresponds to 0 bar positive pressure and thus to the
ambient pressure (atmospheric pressure).
18
Rep. Gr.00 - General, Technical Data
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