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SCXG-SVX01B-EN 97
Owner
Sequence of
Operation
Figure O-SO-2. Typical pulldown curve for unit operating properly within control band.
Figure O-SO-3. Typical pulldown curve for unit operating improperly outside control band.
band according to the desired unit
performance. Increasing the control band
reduces the equipment cycle rate and
increases the maximum potential supply
air temperature deviation from setpoint.
Conversely, decreasing the control band
reduces the maximum potential tem-
perature deviation, but increases the
compressor cycle rate.
Follow these recommendations concern-
ing the supply air temperature control
band settings based on expected unit
sizing:
2 Cooling stage unit: 9 F
3 Cooling stage unit: 7 F
4 Cooling stage unit: 6 F
Low Ambient Compressor Lockout
This function will lock out the compressor
if the outdoor air temperature sensor
reads an outdoor temperature below the
low ambient compressor lockout
temperature setpoint. This setpoint is
adjustable at the human interface panel.
Compressors will lock out when outdoor
air temperature falls below that selected
temperature and will start again when
the temperature rises 5 F above the
setpoint.
Evaporator Coil Frost Protection
FROSTAT
™
The FROSTAT
™
system eliminates the
need for hot gas bypass. It utilizes an
evaporator temperature sensor mounted
on the suction line near the TXV bulb of
each circuit to protect the evaporator
from freezing.
If the evaporator temperature ap-
proaches the specified setpoint (adjust-
able between 25 and 35 F at the HI) the
compressor(s) will cycle off. The supply
fan remains on to help de-ice the coil. The
compressors will restart when the
evaporator temperature has risen 10 F
above the specified cutout temperature
and when the compressor(s) have been
off a minimum of three minutes. This
prevents rapid cycling of the compres-
sors.
Service Valves
Service valves are factory installed on
each circuit before and after the
compressor to allow compressor
isolation for servicing.