23
INSTALLATION AND SERVICE
Refrigerant charging
Oil sight glass
3
.
When the vacuum level of 500
micron is reached, the system must
be isolated from the vacuum pump.
Wait 30 minutes during which the
system pressure should not rise.
When the pressure rapidly increases,
the system is not leak tight. A new
leak detection must be performed
and the vacuum pull-down
procedure should be restarted from
step 1. When the pressure slowly
increases, this indicates the presence
of moisture. In this case step 2 and 3
should be repeated.
4.
If suction and discharge line valves
are used, connect the compressor to
the system by opening the valves.
5.
Break the vacuum with nitrogen or
the fi nal refrigerant.
6.
Repeat step 2 and 3 on the total
system. At commissioning, system
moisture content may be up to 100
ppm. During operation the fi lter drier
must reduce this to a level < 20 ppm.
Warning
: do not use a megohmmeter
or apply power to the compressor
while it is under vacuum, as this may
cause motor winding damage. Never
run the compressor under vacuum as
it may cause compressor motor burn-
out.
"Near-azeotropic" refrigerant mixtures
such as R404A must always be charged
in liquid phase. For the initial charge,
the compressor must not run. Charge
refrigerant as close as possible to the
nominal system charge before starting
the compressor. Then slowly add
refrigerant in the liquid phase, on the
low pressure side as far away as possible
from the running compressor.
The refrigerant charge quantity must
be suitable for both winter and summer
operation. Refer also to section
"Protection against fl ooded starts
and liquid fl oodback" for information
about refrigerant charge limits.
Warning
: when a liquid line solenoid
valve is used, the vacuum in the low
pressure side must be broken before
applying power to the system.
Suction gas superheat
The minimum suction gas superheat
measured on the suction tube 20 cm
far from the compressor body is 8K.
Lower super heat values increase the
risk of unwanted liquid fl oodback to
the compressor.
For very low superheat values an
electronically controlled expansion
valve is recommended.
High superheat can be accepted but in
these cases, tests have to be performed
to check that the maximum discharge
temperature of 130°C will not be
exceeded. Note that high superheat
values decrease the compressor
application envelope and system
performance.
Standard MPZ compressors are
delivered without oil sight glass. The
sight glass can be omitted in most
OEM applications which have run
approval tests to ensure correct oil
and refrigerant circulation.
However, the capacity of the MPZ
range off ers the possibility to use them
in locally constructed refrigeration
applications with remote evaporators,
oil separator and suction accumulator.
In such case, the MPZ with optional
sight glass allows for verifi cation of
the circuit after commissioning and
during maintenance.
The oil sight glass is welded in the
compressor shell. It does not allow for
any other connections.