Volkswagen Polo Service & Repair Manual: Physical Principles

Volkswagen Polo Service & Repair Manual / Refrrigerant R134a Servicing / A/C System, General Information / A/C Technology Basic Principles / Physical Principles

The four known states of water also apply to air conditioning system refrigerants.

1 -	gaseous (invisible)

2 -

vapor

3 -

fluid

4 -

solid

Physical Principles

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. The warmth is extracted from gaseous water, vapor forms first, then water and then ice.

A -	Heat absorption

B -	Heat emission

Physical Principles

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 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.

A/C Technology Basic Principles

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Pressure and Boiling Point

The boiling point given in tables for a liquid is always referenced to an atmospheric pressure of 1 bar (14.5 psi). If the pressure acting on a fluid changes, its boi ...

Other materials:

Checking the electrolyte level of the vehicle battery
Fig. 141 In the engine compartment: removing the vehicle battery cover First read and observe the introductory information and safety warningsThe electrolyte level of the vehicle battery should be checked regularly in high-mileage vehicles, in hot countries and in older vehicle batteries. ...

Information stickers and plates
First read and observe the introductory information and safety warningsSafety certificates, stickers and plates showing important vehicle operation information are factory-fitted in the engine compartment and on certain parts such as the tank flap, front passenger sun visor, the driver door ...

Curtain airbags
Fig. 61 On the left-hand side of the vehicle: location and deployment zone of the curtain airbag First read and observe the introductory information and safety warnings In the interior, a curtain airbag is fitted above the doors on both the driver and front passenger sides . The airbag loca ...