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Installation

Leak detection

Leak detection must be carried out using a
mixture of nitrogen and refrigerant or nitrogen
and helium, as indicated in the table below.
Never use other gasses such as oxygen, dry air
or acetylene as these may form an inflammable
mixture.

Pressurize the system on HP side first then LP
side.

Leak detection

with refrigerant

Leak detection

with a mass spectrometer

Nitrogen & R410A

Nitrogen & Helium

Vacuum pump down and

moisture removal

Refrigerant charging

Moisture obstructs the proper functioning
of both the compressor and the refrigeration
system. Air and moisture reduce service life and
increase condensation pressure, which causes
abnormally high discharge temperatures that
are then capable of degrading the lubricating
properties of the oil. The risk of acid formation
is also increased by air and moisture, and this
condition can also lead to copper plating. All

these phenomena may cause both mechanical
and electrical compressor failures. The typical
method for avoiding such problems is a vacuum
pump-down executed with a vacuum pump, thus
creating a minimum vacuum of 500 microns (0.67
mbar). Please refer to News bulletin
Tl1-026-0302 “Vacuum pump down and
dehydration procedure”.

For the initial charge the compressor must not
run and eventual service valves must be closed.
Charge refrigerant as close as possible to the
nominal system charge before starting the
compressor. This initial charging operation must
be done in liquid phase as far away as possible
from the compressor. The best location is on the
liquid line between the condenser outlet and the
filter drier. Then during commissioning, when
needed, a complement of charge can be done

in liquid phase: slowly throttling liquid in on the
low pressure side as far away as possible from the
compressor suction connection. The refrigerant
charge quantity must be suitable for both
summer and winter operations.

Refer to news bulletin FRCC.EN.050 “Danfoss
Commercial Compressors recommended
refrigerant system charging practice” for more
details.

Loss of charge protection

Customer need to protect compressor against
loss of charge. Compared with fix speed
compressor, loss of charge could be more severe
to variable speed compressors. When loss of
charge occurs, variable speed compressors will
speed up to compensate capacity reduction,
Further drive will active derating function to
slow compressor heating up. Thus compressors

will run longer time at high temperature but
low oil viscosity than fixed speed and will lead
to compressor damage eventually. Low pressure
switch and discharge gas thermostat could
protect loss of charge somehow. But it is highly
recommended to protect compressor from high
superheat.

System pressure test

Always use an inert gas such as nitrogen for
pressure testing. Never use other gasses such as
oxygen, dry air or acetylene as these may form

an inflammable mixture. Do not exceed the
following pressures:

Pressurize the system on HP side first then LP side
to prevent rotation of the scroll. Never let the

pressure on LP side exceed the pressure on HP
side with more than 5 bar.

Maximum compressor test pressure (low side)

33.3 bar(g) for VZH088 & 117
30.2 bar(g) for VZH170

Maximum compressor test pressure (high side)

45 bar (g)

Maximum pressure difference between high and low side

of the compressor

37 bar