Midea MUE-48HRFN1-M, Service Manual

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75
Ice-blockage shall cause abnormal
operation of system, while copper oxide
shall damage compressor.

Eliminating the non-condensable gas (air)
in system to prevent the components
oxidizing, pressure fluctuation and bad heat
exchange during the operation of system.
12.6.2 Selection of vacuum pump

The ultimate vacuum degree of vacuum
pump shall be -756mmHg or above.

Precision of vacuum pump shall reach
0.02mmHg or above.
12.6.3 Operation procedure for vacuum
drying
Due to different construction environment, two
kinds of vacuum drying ways could be chosen,
namely ordinary vacuum drying and special
vacuum drying.
1 Ordinary vacuum drying

When conduct first vacuum drying,
connect pressure gauge to the infusing
mouth of gas pipe and liquid pipe, and
keep vacuum pump running for 1hour
(vacuum degree of vacuum pump shall be
reached -755mmHg).

If the vacuum degree of vacuum pump
could not reach -755mmHg after 1 hour of
drying, it indicates that there is moisture or
leakage in pipeline system and need to go
on with drying for half an hour.

If the vacuum degree of vacuum pump still
could not reach -755mmHg after 1.5 hours
of drying, check whether there is leakage
source.

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.
2 Special vacuum drying
The special vacuum drying method shall be
adopted when:

Finding moisture during flushing refrigerant
pipe.

Conducting construction on rainy day,
because rain water might penetrated into
pipeline.

Construction period is long, and rain water
might penetrated into pipeline.

Rain water might penetrate into pipeline
during construction.
Procedures of special vacuum drying are as
follows:

Vacuum drying for 1 hour.

Vacuum damage, filling nitrogen to reach
0.5Kgf/cm2 .
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