C6.2.44/0219/E
23
consideration is the minimum run time required to return oil to the compressor after start-up. To
establish the minimum run time obtain a sample compressor equipped with a sight tube (available
from Emerson) and install it in a system with the longest connecting lines that are approved for
the system. The minimum on time becomes the time required for oil lost during compressor start-
up to return to the compressor sump and 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 Sound characteristics
For the Copeland Scroll Digital compressor the sound spectrum of the loaded state and that of the
unloaded state are quite different. The unloaded sound power is normally 2 dB(A) higher than the
loaded sound power. If sound variability is an issue, we recommend the use of a sound cover.
5.15 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.
5.16 Frequency
There is no general release of standard Copeland scroll compressors for use with variable speed
AC drives. There are numerous issues that must be considered when applying Scroll compressors
with variable speed, including system design, inverter selection, and operating envelopes at
various conditions. Only frequencies from 50 Hz to 60 Hz are acceptable. Operation outside this
frequency range is possible but should not be done without specific Application Engineering
review. The voltage must vary proportionally to the frequency.
If the inverter can only deliver a maximum voltage of 400V, the amps will increase when the speed
is above 50 Hz, and this may give rise to nuisance tripping if operation is near the maximum power
limit and/or compressor discharge temperature limit.
5.17 Oil level
The oil level should be maintained at mid-point of the sight glass. If an oil regulator is used the
level should be set within the top half of the sight glass.
5.18 Digital system control
Due to the pulsing characteristic of Copeland Scroll Digital compressors superheat control needs
to be performed by qualified solutions in order to ensure the stability, reliability and good
performance of the system.
NOTE: For further information about these solutions see Technical Information C7.8.3
"Refrigeration
– Controlling Digital Scroll".
5.19 Power factor
During the loaded state, when the Copeland Scroll Digital compressor operates at full capacity,
the power factor is almost the same as with a standard scroll. However, when the scrolls are
unloaded, the power factor is lower.
