Porsche P-80 2005, Руководство пользователя

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Climate Control Systems Diagnosis & Repair
Air Conditioning Basics
1. Heat always flows from hot to cold.
Heat is a form of energy. Cold is a term that means less
heat is present. Cold materials contain less heat energy
than hot materials and heat always flows from the hotter
material to the colder.
For example, if you hold an ice cube, your hand will feel
cold. The ice removes heat from your hand and you sense
the loss of heat. If you touch something warm, you feel the
heat flowing into your hand. If a large amount of heat
transfers, you may be burned and feel pain.
Practical Application
• Heat energy contained in the passenger compartment
air is absorbed by the cold refrigerant in the A/C evapo-
rator.
• Hot refrigerant gives off heat and is cooled by cooler
ambient air flowing through the A/C condenser.
In both cases, heat moves from hotter to cooler.
Notes:
2. Materials absorb or give off large amounts of
heat when changing state.
Sweating makes us feel cooler. As liquid water on our skin
evaporates, it removes body heat. In a similar way, refrig-
erant vaporizing (changing from liquid to gas) inside the
A/C evaporator absorbs heat from the warmer air around
the evaporator.
Practical Application
• In the evaporator, liquid refrigerant boils at
temperatures below the temperature of the air in the
passenger compartment. The refrigerant absorbs large
quantities of heat, far more heat than it would if it
remained a liquid.
• In the condenser, the reverse takes place. Here, hot
refrigerant gas condenses back to liquid and gives off
large amounts of heat to the cooler atmosphere. The
refrigerant gives up far more heat than it would if it
remained a gas.
To explain, we need to look at two kinds of heat energy:
Sensible Heat and Latent Heat.
Sensible Heat – is measurable heat - a measurable
change in the temperature of a material. Adding heat
energy raises the measurable temperature of a material
and increases Sensible Heat. If we heat a pot of water on
a stove, the temperature of the water will increase and we
can measure this change with a thermometer (see illustra-
tion, below).
Latent Heat – is heat energy that is added to a material
Sensible Heat
Heat energy
increases
temperature
of liquid
No change
of state