Procedures of special vacuum drying are as
follows:
Vacuum drying for 1 hour.
Vacuum damage, filling nitrogen to reach
0.5Kgf/cm
2
.
Because nitrogen is dry gas, vacuum
damage could achieve the effect of
vacuum drying, but this method could not
achieve drying thoroughly when there is
too much moisture. Therefore, special
attention shall be drawn to prevent the
entering of water and the formation of
condensate water.
Vacuum drying again for half an hour.
If the pressure reaches -755mmHg, start
to pressure leakage test. If it cannot reach
the value, repeat vacuum damage and
vacuum drying again for 1 hour.
Leakage test: After the vacuum degree
reaches -755mmHg, stop vacuum drying
and keep the pressure for 1 hour. If the
indicator of vacuum gauge does not go up,
it is qualified. If going up, it indicates that
there is moisture or leak source.
12.7 Additional refrigerant charge
After the vacuum drying process is carried
out, the additional refrigerant charge
process needs to be performed.
The outdoor unit is factory charged with
refrigerant. The additional refrigerant
charge volume is decided by the diameter
and length of the liquid pipe between indoor
and outdoor unit. Refer the following
formula to calculate the charge volume.
Diameter of
liquid pipe
(mm)
V: Additional refrigerant charge volume (g).
L: The length of the liquid pipe (m).
Note:
Refrigerant may only be charged after
performed the vacuum drying process.
Always use gloves and glasses to protect
your hands and eyes during the charge
work.
Use electronic scale or fluid infusion
apparatus to weight refrigerant to be
recharged. Be sure to avoid extra
refrigerant charged, it may cause liquid
hammer of the compressor or protections.
Use supplementing flexible pipe to connect
refrigerant cylinder, pressure gauge and
outdoor unit. And the refrigerant should be
charged in liquid state. Before recharging,
the air in the flexible pipe and manifold
gauge should be exhausted.
After finished refrigerant recharge process,
check whether there is refrigerant leakage
at the connection joint part. (Using gas
leakage detector or soap water to detect).
12.8 Engineering of insulation
12.8.1 Insulation of refrigerant pipe
1 Operational procedure of refrigerant
pipe insulation
Cut the suitable pipe → insulation (except joint
section) → flare the pipe → piping layout and
connection→ vacuum drying → insulate the
joint parts
2 Purpose of refrigerant pipe insulation
During operation, temperature of gas pipe
and liquid pipe shall be over-heating or
over-cooling extremely. Therefore, it is
necessary to carry out insulation; otherwise
it shall debase the performance of unit and
burn compressor.
Gas pipe temperature is very low during
cooling. If insulation is not enough, it shall
form dew and cause leakage.
Temperature of gas pipe is very high
(generally 50-100 ℃ ) during heating.
Insulation work must be carried out to
prevent hurt by carelessness touching.
3 Insulation material selection for
refrigerant pipe
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