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of start assist devices in most applications. However,
if low voltage conditions exist at start up, protector
trips can result. Therefore, start assist devices (start
capacitors and relays) are available to maximize starting
characteristics under abnormal conditions.
Fusite
Fusite pin orientation for single-phase and three- phase
refrigeration scroll compressors are shown in Figure 4
and inside the terminal box.
Shell Temperature
CAUTION
System component failure may cause the top shell and
discharge line to briefl y reach temperatures above 300°F.
Wiring or other materials, which could be damaged by
these temperatures, should not come in contact with
the shell.
Connection Fittings
Scroll compressors are provided with either braze
connections or roto-lock adapters depending on the bill
of material selected (reference AE4-1219 for roto-lock
torque values). Consult your District Sales Manager or
Application Engineer for details.
All ZBKC/E models have copper plated steel suction
and discharge fi ttings for a more rugged, leak resistant
connection.
See section on New Installation (see Figure 6) for
suggestions on how to properly braze these fi ttings.
Three-Phase Rotation Direction
Scroll compressors are directional dependent: i.e., they
will compress in one rotational direction only. On single-
phase compressors, this is not an issue since they will
only start and run in the proper direction (except as
described in the Labeled Brief Power Interruptions).
Three-phase scrolls, however, will rotate in either
direction depending on the power of the phasing. So
there is a 50/50 chance of connected power being
"backwards." Contractors should be warned of this.
Appropriate instructions or notices should be provided
by the Original Equipment Manufacturer.
Verifi cation of proper rotation can be made by observing
that the suction pressure drops and the discharge
pressure rises when the compressor is energized.
Additionally, if operated in reverse the compressor is
noisier and its current draw is substantially reduced
compared to tabulated values.
Although operation of scroll in reverse direction for brief
© 2014 Emerson Climate Technologies, Inc.
Printed in the U.S.A.
Application Engineering
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periods of time is not harmful, continued operation could
result in failure.
All three-phase compressors are wired identically
internally. Once the correct phasing is determined for
a specifi c system or installation, connecting properly
phased power leads to the same fusite terminals will
maintain the proper rotation.
Brief Power Interruptions
Brief power interruptions (less than ½ second) may
result in powered reverse rotation of single-phase
refrigeration scroll compressors. High-pressure
discharge gas expands backward through the scrolls
at power interruption causing the scroll to orbit in
the reverse direction. If power is reapplied while this
reversal is occurring, the compressor may continue to
run noisily in the reverse direction for several minutes
until the compressor internal protector trips. This has no
negative effect on durability. When the protector resets,
the compressor will start and run normally.
Emerson strongly encourages the use of a timer
which can sense brief power interruptions and lock the
compressor out of operation for two minutes. A typical
timer circuit is shown in Figure 5.
No time delay is required on three phase models to
prevent reverse rotation due to power interruptions
Deep Vacuum Operation
WARNING
Do not run a refrigeration scroll compressor in a
vacuum. Failure to heed this advice can result in
permanent damage to the compressor.
A low-pressure control is required for protection against
vacuum operation. See the section on pressure controls
for the proper set points. (See Table 5)
Scroll compressors (as with any refrigeration compressor)
should never be used to evacuate refrigeration or air
conditioning systems. See AE24-1105 for proper system
evacuation procedures.
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
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