Compressor Replacement After Motor Burn; System Charging Procedure; Unbrazing System Components - Emerson ZB Copeland Scroll Product Manual

ZB
Series
Application Guide
Field Service

Unbrazing System Components

CAUTION!
If the refrigerant charge is removed from a scroll unit by bleeding the
high side only, it is sometimes possible for the scrolls to seal preventing
pressure equalization through the compressor. This may leave the low
side shell and suction line tubing pressurized. If a brazing torch is then
applied to the low side, the pressurized refrigerant oil mixture could
ignite as it escapes and contacts the brazing flame. It is important to
check both the high and low sides with manifold gauges before unbrazing.
In the case of an assembly line repair, remove the refrigerant from both
the high and low sides. Instructions should be provided in appropriate
product literatures and assembly areas
• To disconnect: Reclaim refrigerant from both the high and low side of
the system. Cut tubing near compressor.
• To reconnect. Recommended brazing material is Silfos with minimum
5% silver or silver braze material with flux. Insert tubing stubs into
fitting and connect to the system with tubing connectors. Follow New
Installation brazing instructions.
Brazing Procedure
Figure 2 discusses the proper procedures for brazing the suction and
discharge lines to a Copeland Scroll compressor. It is important to flow
nitrogen through the system while brazing all joints during the system
assembly process. Nitrogen displaces the air and prevents the formation
of copper oxides in the system.
If allowed to form, the copper oxide flakes can later be swept through
the system and block screens such as those protecting capillary tubes,
thermal expansion valves, and accumulator oil return holes. The blockage
- whether it is of oil or refrigerant - is capable of doing damage resulting
in compressor failure.

6.2 Compressor Replacement after Motor Burn

In the case of a motor burn, the majority of contaminated oil will be
removed with the compressor. The rest of the oil is cleaned through use
of suction and liquid line filter dryers. A 100% activated alumina suction
filter drier is recommended but must be removed after 72 hours. Separate
bulletins are available on request for clean up procedures and for liquid
line filter drier recommendations. AE Bulletin 24-1105 for clean up
procedures AE Bulletin 11-1297 for liquid line filter drier recommendations.
It is highly recommended that the suction accumulator be replaced if
the system contains one. This is because the accumulator oil return
orifice or screen may be plugged with debris or may become plugged
shortly after a compressor failure. This will result in starvation of oil to
the replacement compressor and a second failure.

6.3 System Charging Procedure

Systems should be charged with liquid on the high side to the extent
possible. The majority of the charge should be pumped into the high side
of the system to prevent hi pot failures, and bearing washout during first
time start. If additional charge is needed, it should be added as liquid, in
a controlled manner, to the low side of the system with the compressor
operating. Pre-charging on the high side and adding liquid on the low side
of the system are both meant to protect the compressor from operating
with abnormally low suction pressures during charging.
Do not start the compressor while the system is in a deep vacuum. Internal
arcing may occur when a compressor is started in a vacuum Do not operate
compressor without enough system charge to maintain at least 7 psig
(0.5Kg/cm²) suction pressure. Do not operate with a restricted suction.
Do not operate with the low pressure cut-out jumpered. Allowing pressure
to drop below 2°F(-16°C) for more than a few seconds may overheat scrolls
and cause early drive bearing damage or cause the scroll temperature
protection to activate. Do not use compressor to test opening set point
of high pressure cutout. Bearings are susceptible to high load damage
before they have had several hours of normal running for proper break in.
Never install a system in the field and leave it unattended with no charge,
or with the service valves closed without securely locking out the system.
This will prevent unauthorized personnel from accidentally operating the
system and potentially ruining the compressor by operating with no
refrigerant flow.
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