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than reciprocating compressor discharge reeds, normally used with pumpdown, causing the scroll
compressor to recycle more frequently. Repeated short cycling of this nature can result in a low oil
situation and consequent damage to the compressor. The hysteresis of the low-pressure control
differential has to be reviewed since a relatively large volume of gas will re-expand from the high side
of the compressor into the low side after shutdown.
For pressure control setting, never set the low-pressure limiter to shut off outside of the
operating envelope. To prevent the compressor from running into problems during such
faults as loss of charge or partial blockage, the low-pressure limiter shall not be set lower
than the minimum suction pressure allowed by the operating envelope.
5.13 Minimum run time
Emerson recommends a maximum of 10 starts per hour. There is no minimum off time because
scroll compressors start unloaded, even if the system has unbalanced pressures. The most critical
consideration is the minimum run time required to return oil to the compressor after start-up. To
establish the minimum run time, a sample compressor equipped with an external oil sight glass is
available from Emerson. The minimum on time becomes the time required for oil lost during
compressor start-up to return to the compressor sump and to restore a minimal oil level that will
ensure oil pick-up through the crankshaft. Cycling the compressor for a shorter period than this, for
instance to maintain very tight temperature control, will result in progressive loss of oil and damage
to the
compressor.
5.14 Shut-off sound
Scroll compressors incorporate a device that minimizes reverse rotation. The residual momentary
reversal of the scrolls at shut-off will cause a clicking sound, but it is entirely normal and has no effect
on compressor durability.
5.15 Supply frequency and voltage
There is no general release of standard Copeland scroll compressors for use with variable speed AC
drives. A number of considerations must be taken into account when applying scroll compressors
with variable speed, including system design, inverter selection, and operating envelopes at various
conditions. Only frequencies from 50 to 60 Hz are acceptable.
The last letter of the motor code indicates which frequency and voltage must be applied – see
section 2.2 "Nomenclature".
50 Hz
220-240 V / 1 ph
380-420 V / 3 ph
460 V / 3 ph
Table 12: Electrical code for motors
5.16 Oil level
There is no oil sight glass on ZH*KCU compressors.
Some systems may contain higher than normal refrigerant charges. Systems with large coils, low
ambient condenser flooding, or systems with multiple heat exchangers are some of the
configurations that may require additional lubricant.
During the system development phase, adequate oil return from the system to the compressor should
be evaluated and qualified. For this purpose, a sample compressor for lab testing, equipped with an
external oil sight tube, is available from Emerson. See also section 3.16 "Compressor oil return,
oil balancing, refrigerant floodback and oil dilution tests".
BOM versions 434 and 424 contain a stub tube connection 7/8" (22.2 mm) for paralleling on the
compressor housing at oil level height.
If an oil regulator is used the oil level should be set within the top half of the oil regulator sight glass.
A sample compressor is shown in Figure 21 below. The dimensions of the level glass are shown in
Table 13.
AGL_HP_ST_ZHKCU_EN_Rev01
60 Hz
Code
-
Z
D
27
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