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© 2015 Emerson Climate Technologies, Inc.
AE4-1331 R7
Reversing Valves
Since Copeland Scroll compressors have very high
volumetric efficiency, their displacements are lower
than those of comparable capacity reciprocating
compressors.
CAUTION
Reversing valve sizing must
be within the guidelines of the valve manufacturer.
Required pressure drop to ensure valve shifting
must be measured throughout the operating range
of the unit and compared to the valve manufacturer's
data. Low ambient heating conditions with low flow
rates and low pressure drop across the valve can
result in a valve not shifting. This can result in a
condition where the compressor appears to be
not pumping (i.e. balanced pressures). It can also
result in elevated compressor sound levels.
During
a defrost cycle, when the reversing valve abruptly
changes the refrigerant flow direction, the suction
and discharge pressures will go outside of the normal
operating envelope. The sound that the compressor
makes during this transition period is normal, and the
duration of the sound will depend on the coil volume,
outdoor ambient, and system charge. The preferred
method of mitigating defrost sound is to shut down the
compressor for 20 to 30 seconds when the reversing
valve changes position going into and coming out of
the defrost cycle. This technique allows the system
pressures to reach equilibrium without the compressor
running. The additional start-stop cycles do not
exceed the compressor design limits, but suction and
discharge tubing design should be evaluated.
The reversing valve solenoid should be wired so
that the valve does not reverse when the system is
shut off by the operating thermostat in the heating
or cooling mode. If the valve is allowed to reverse at
system shutoff, suction and discharge pressures are
reversed to the compressor. This results in pressures
equalizing through the compressor which can cause
the compressor to slowly rotate backwards until the
pressures equalize. This condition does not affect
compressor durability but can cause unexpected sound
after the compressor is turned off.
Low Ambient Cut-Out
A low ambient cut-out is not required to limit air-to air
heat pump operation. Air-to-water heat pumps must
be reviewed since this configuration could possibly run
outside of the approved operating envelope (
Figure 7
)
causing overheating or excessive wear.
Oil Type
Polyol ester (POE) oil is used in these compressors.
See the compressor nameplate for the original oil
charge. A complete recharge should be approximately
four fluid ounces (118 ml) less than the nameplate
value. If additional oil is needed in the field, Copeland
™
Ultra 32-3MAF, Lubrizol Emkarate RL32-3MAF, Parker
Emkarate RL32-3MAF/(Virginia) LE32-3MAF, or Nu
Calgon 4314-66 (Emkarate RL32-3MAF) should be
used. Copeland
™
Ultra22 CC, Hatcol EAL22CC, and
Mobil EAL Arctic 22 CC are acceptable alternatives.
CAUTION! POE must be handled carefully and
the proper protective equipment (gloves, eye
protection, etc.) must be used when handling POE
lubricant. POE must not come into contact with any
surface or material that might be harmed by POE,
including without limitation, certain polymers (e.g.
PVC/CPVC and polycarbonate).
Contaminant Control
Copeland Scroll
compressors leave the factory with
a miniscule amount of contaminants. Manufacturing
processes have been designed to minimize the
introduction of solid or liquid contaminants. Dehydration
and purge processes ensure minimal moisture levels
in the compressor and continuous auditing of lubricant
moisture levels ensure that moisture isn’t inadvertently
introduced into the compressor.
It is generally accepted that system moisture levels
should be maintained below 50 ppm.
A filter-drier is
required on all R-410A and POE lubricant systems
to prevent solid particulate contamination, oil
dielectric strength degradation, ice formation, oil
hydrolysis, and metal corrosion.
It is the system
designer’s responsibility to make sure the filter-drier is
adequately sized to accommodate the contaminants
from system manufacturing processes that leave
solid or liquid contaminants in the evaporator coil,
condenser coil, and interconnecting tubing plus any
contaminants introduced during the field installation
process. Molecular sieve and activated alumina are
two filter-drier materials designed to remove moisture
and mitigate acid formation. A 100% molecular sieve
filter can be used for maximum moisture capacity. A
more conservative mix, such as 75% molecular sieve
and 25% activated alumina, should be used for service
applications.
Long Line Sets/High Refrigerant Charge
Some system configurations may contain higher-than-
normal refrigerant charges either because of large
internal coil volumes or long line sets. If such a system
also contains an accumulator then the permanent
loss of oil from the compressor may become critical.
If the system contains more than 20 pounds (9 kg) of
refrigerant, it is our recommendation to add one fluid
ounce of oil for every 5 pounds (15 ml/kg) of refrigerant
