A normally closed solenoid valve is required in the
interstage line feeding each compressor on a par-
allel rack as shown in the refrigerant piping
schematic. This valve is required to eliminate inter-
stage to suction pressure leak back during the off
cycle of any compressor. When any compressor
on the rack turns off, its respective interstage
solenoid valve must close and when it turns on its
respective interstage solenoid valve must open.
The solenoid valve must be properly wired to the
Carlyle module (per installation instructions) of the
compressor it is controlling.
Check valves are also required in the interstage
line feeding each compressor on a parallel rack as
shown. The check valve must be located
upstream of the motor cooling valve for each
compressor and downstream of the solenoid valve.
The check valves are used to eliminate the possibility
of reverse flow from any compressor economizer
port.
Carlyle also recommends that separate subcoolers be
used for each different saturated suction tempera-
ture group. Compressors operating with different sat-
urated suction temperatures will have a significant
difference in interstage pressure. The resulting
amount of subcooling will be lower than stated in the
rating tables and overall rack capacity will reduce.
Individual subcoolers will also result in more stable
subcooler control as compressors cycle (which would
significantly vary the interstage pressure, causing the
subcooler expansion valve
to hunt).
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