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AGL_HP_ST_ZHK1P_EN_Rev00

situation and consequent damage to the compressor. The hysteresis of the low-pres sure c ontrol
dif ferential has to be reviewed since a relatively large volume of gas will re-expand f rom t he hig h
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 should not be set lower
than the minimum suction pressure allowed by the operating envelope.

5.11 Pump-out cycle

A pump-out cycle has been successfully used by some manufacturers of large rooftop units. Af t er
an extended off period, a typical pump-out cycle will energize the compressor for up to one second
f ollowed by an off time of 5 to 20 seconds. This cycle is usually repeated a second time, t he t hird
time the compressor stays on for the cooling cycle.

5.12 Minimum run time

Emerson recommends a maximum of 10 starts per hour. There is no minimum of f t ime b ecause
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 af t er s tart -up. To
establish the minimum run time, a sample compressor equipped with an external oil sight g las s is
available  f rom  Emerson.  The  minimum  on  time becomes the time required f or oil lost during
compressor start-up to return to the compressor sump and to restore a minimal o il lev el t hat  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.

5.13 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
ef f ect on compressor durability.

5.14 Supply frequency and voltage

There is no general release of standard Copeland scroll compressors for use with variable s peed
AC  drives.  There  are  numerous  issues  that  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 Hz to 60 Hz are acceptable. Operation
outside this frequency range is possible but should not  be d one without  s pecif ic A pplicat ion
Engineering review. The voltage must vary proportionally to the frequency.

If the inverter can only deliver a maximum voltage of 400 V, 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.

The last digit of the model motor code indicates which frequency and voltage must b e applied

–

see

section 2.2 "Nomenclature"

. The availability of codes per compressor model can be checked

section 2.1 "Compressor range"

50 Hz

60 Hz

Code

380

– 420 – 3 ph

460