McQuay MWM 007F, Manual

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b) Ensure that the compressor is not expose to open air for more than the recommended time
specified by its manufacturer (typically less than 10 minutes). Removed the seal-plugs only when
the compressor is about to be brazed.
c) The system should be thoroughly vacuumed to 1.0 Pa (-700mmHg) or lower. This vacuuming level
is more stringent than R22 system so as to ensure no incompressible gas and moisture in the
system.
d) When charging R407C, ensure that only liquid is being withdrawn from the cylinder or can. This is
to ensure that only the original composition of R407C is being delivered into the system. The liquid
composition can be different from the vapor composition.
R32/R125/R134
33% / 33% / 34%
23% / 25% / 52%
Composition of R407C in vapour phase
is different from liquid phase.
e) Normally, the R407C cylinder or can is being equipped with a dip-pipe for liquid withdrawal.
However, if the dip-pipe is not available, invert the cylinder or can so as to withdraw liquid from the
valve at the bottom.
Dip-pipe Invert cylinder
without dip-pipe
Liquid
withdrawal
f) When servicing leak, the top-up method, commonly practiced for R22 system, is not recommended
for R407C system. Unlike R22 where the refrigerant is of a single component, the composition of
R407C, which made-up of three different components, may have changed during the leak.
Consequently, a top-up may not ensure that the R407C in the system is of original composition.
This composition shift may adversely affect the system performance. It is recommended that the
system should be evacuated thoroughly before recharging with R407C.
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