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:

Extraction System Group Classifications
At this time, A/C service units for extracting, cleaning and filling refrigerant for motor vehicle A/C systems are available from various manufacturers. Group 3: Mobile extraction and charging systems for filling c ...

Checking the coolant level and refilling coolant
Fig. 139 In the engine compartment: mark on the coolant expansion tank Fig. 140 In the engine compartment: coolant expansion tank cap First read and observe the introductory information and safety warningsThe warning lamp for the engine coolant will light up if the engine coolant level i ...

Wheel bolt caps
Fig. 165 Removing the wheel bolt caps First read and observe the introductory information and safety warnings Take the wire hook from the vehicle toolkit . Insert the hook through the opening in the cap and pull off in the direction of the arrow. The caps protect the wheel b ...