Tadano TR-800XXL4, Service Manual

Page: 190 / 402

K - 2 K - 2
Air Conditioner
7 W701-0220E
3.3 Refrigerant
1. The substance that circulates through the
refrigeration cycle, and functions to transmit heat,
is known as the refrigerant. In our air conditioning
system, HFC134a is used. It is a freon-based
refrigerant, but does not contain chlorine.
2. As shown in the figure below, the refrigerant
HFC134a remains in liquid form at relatively high
temperatures when it is strongly compressed.
However, at low pressures it vaporizes at
temperatures as low as 0°C (32°F) or
-10°C (14°F).
3. This means, for example, that if the refrigerant
vaporizes at 0°C (32°F), then the evaporator is
also at 0°C (32°F). The air that passes through
this evaporator should be cooled.
4. If the pressure is reduced so that the refrigerant
evaporates at -5°C (23°F), the evaporator is also
maintained at -5°C (23°F). This results in the
formation of frost, which inhibits the flow of air
through the evaporator and prevents cooling.
5. The vaporized refrigerant must then be liquefied.
However, it is impossible to obtain a temperature
as low as 40°C (104°F) in a hot summer
environment.
6. If 60
°
C (140°F) is possible, HFC134a will become
a liquid at 60°C (140°F) if the pressure is
approximately 1.7 MPa (246.5 psi) or above.
When the gaseous refrigerant is compressed to
1.7 MPa (246.5 psi) (by the compressor), the gas
temperature rises to approximately 80°C (176°F).
7. Therefore, the temperature of the gas as it enters
the condenser is 80°C (176°F). The curve above
shows that when the refrigerant gas is cooled by
20°C (68°F), it becomes a liquid at approximately
60°C (140°F) by the time it reaches the condenser
outlet.