AE4-1312 R2
© 2010 Emerson Climate Technologies
Printed in the U.S.A.
6
There is no negative impact on durability caused by
operating three phase Copeland Scroll compressors in
the reversed direction for a short period of time (under
one hour) but oil may be lost. After several minutes of
reverse operation, the compressor’s internal protector
will trip. If allowed to repeatedly restart and run in
reverse without correcting the situation, the compressor
will be permanently damaged because of oil loss to
the system. Oil loss can be prevented during reverse
rotation if the tubing is routed at least six inches (15
cm) above the compressor. All three-phase scroll
compressors are wired identically internally. As a result,
once the correct phasing is determined for a specific
system or installation, connecting properly phased
power leads to the identified compressor electrical
(Fusite) terminals will maintain proper rotation direction.
See
Fig 4.
It should be noted that all three phase scrolls
will continue to run in reverse until the protector opens
or the phasing is corrected.
Brief Power Interruptions
Brief power interruptions (less than 1/2 second) may
result in powered reverse rotation of single-phase
Copeland Scroll compressors. This occurs because
high-pressure discharge gas expands backward through
the scrolls during power interruption, causing the scroll
to orbit in the reverse direction. When power is reapplied
while reverse rotation is occurring, the compressor may
continue to run in the reverse direction for some time
before the compressor’s internal protector trips. This
has no effect on durability. When the protector resets,
the compressor will start and run normally.
To avoid disruption of operation, an electronic control
that can sense brief power interruptions may be used
to lock out the compressor for a short time. This control
could be incorporated in other system controls (such
as defrost or thermostat), or be a stand-alone control.
Functional specifications for this control as well as a
suggested wiring diagram are shown in
Figure 3
.
Because three-phase models have high enough torque
to prevent reverse rotation after power interruptions no
time delay is necessary.
ASSEMBLY LINE PROCEDURES
Installing the compressor
Scroll compressors leave the factory dehydrated with
a positive dry air charge. Plugs should not be removed
from the compressor until the compressor has had
sufficient time to warm up if stored outside and is ready
for assembly to the unit. It is suggested that the larger
suction plug be removed first to relieve the internal
pressure. Removing the smaller discharge plug could
result in a spray of oil out of this fitting since some oil
would accumulate in the head of the compressor after
Emerson test runs the compressor. The inside of both
fittings should we wiped with a lint free wipe to remove
residual oil prior to brazing. A compressor containing
mineral oil should never be left open longer than 15
minutes or 5 minutes if it contains POE oil.
Assembly Line Brazing Procedure
Figure 6
discusses the proper procedures for brazing
the suction and discharge lines to a 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 resulting
blockage of oil or refrigerant may do damage resulting
in compressor failure.
Pressure Testing
The pressure used on the line to meet the UL burst
pressure requirement
can not
be higher than
400 psig.
Higher pressure might result in permanent deformation
of the compressor shell and possibly cause rotor slip.
Assembly Line System Charging Procedure
Systems should be charged on both the high and low
sides simultaneously. The majority of the charge should
be placed in the high side of the system to prevent low
volt start difficulties, Hipot failures, and bearing washout
during first-time start on the assembly line. It is best to
charge only vapor into the low side of the system.
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 disabled.
Allowing pressure to drop below 7 psig
(0.5 kg/cm2) for more than a few seconds may overheat
scrolls and cause early drive bearing damage. Do not
use compressor to test opening set point of a high
pressure cutout. Bearings are susceptible to damage
before they have had several hours of normal running
for proper break in.
“Hipot” (AC High Potential) Testing
Copeland Scroll compressors are configured with the
motor down and the pumping components at the top
of the shell. As a result, the motor can be immersed
in refrigerant to a greater extent than hermetic
reciprocating compressors when liquid refrigerant is
present in the shell. In this respect, the scroll is more like
