22
(c) Ensure that the compressor is not exposed to open air for more than the recommended time specied
by its manufacturer (typically less than 10 minutes). Remove the seal-plug only when the compressor is
about to be brazed.
(d) The system should be thoroughly vacuumed to 1.0 Pa (-700mmHg) or lower. This vacuuming level is more
stringent then R22 system so as to ensure no incompressible gas and moisture in the system.
(e) When charging R407C, ensure that only liquid is being withdrawn from the cylinder or can. This is to en-
sure that only the original composition of R407C is being delivered into the system. The liquid composition
can be different from the vapour composition.
R32/R125/R134
23% / 25% / 52%
33% / 33% / 34%
Composition of R407C in vapour phase
is different from liquid phase.
(f) 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
Liquid withdrawal
Invert cylinder
without dip-pipe
(g) When servicing leaks, the top-up method, commonly practiced for R22 system, is not recommended for
R407C systems. Unlike R22 where the refrigerant is of a single component the composition of R407C
(which is 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 the original composition. This composition
shift may adversely affect the system performance. It is recommended that the system by evacuated
thoroughly before recharging with R407C.
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