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Form 201.23-NM2
Issue date: 12/19/2023
Due to the short duration of the open and close step-
per pulses, LED lighting will be difficult to observe.
In rare cases where validation of the controller output
and valve movement needs to be checked, the valves
can be operated in Service Mode. When operated in
Service Mode, visual indication of the LED's lighting
will be more obvious. Generally, no audible noise is
evident as the valves open and close unless the valve
is being run against its stop. It is possible to obtain an
indication of valve movement by touch, when a valve
is opening or closing.
Manually operating the Feed and Drain
Valves in Service Mode can drain or over-
fill the flash tank. This could cause valve
movements and levels in the flash tank
to act out of the ordinary when a system
first starts, until the Chiller Control Board
brings the flash tank level and superheat
under control. This may also be evident in
the flash tank level and open/close % on
the displays. It may also cause the liquid
line or flash tank sight glasses to empty or
the flash tank sight glass to fill.
Careless use of manual control could
cause liquid damage to the compressor
when it is started.
Economizer control
The Economizer Solenoid controls a vapor feed to the
economizer port on the compressor from the top of the
flash tank. When the valve is open, refrigerant gases
off in the flash tank providing additional subcooling to
the liquid in the tank. The subcooled liquid is then fed
to the evaporator resulting in additional system capac-
ity and efficiency.
In normal operation, the Economizer Solenoid on a
compressor will be turned on whenever the VSD fre-
quency is more than 120 Hz, the flash tank level is less
than 75%, motor current less than 80%FLA, motor
temperature sensors are all less than less than150°F,
and the economizer timer is timed out. Whenever the
Economizer Solenoid is turned on, the compressor load
timer is set to 35 seconds and economizer timers for
every system are set to 30 seconds, unless they are al-
ready above 30 seconds.
Johnson Controls
In low ambient temperatures less than 40°F, run time
on the respective compressor is less than 5 minutes,
and the flash tank level is less than75%, the system
Economizer Solenoid is turned on. Under these con-
ditions, the VSD frequency and the motor temp sen-
sor readings are not factors that could overload the
compressor. Energizing the Economizer Solenoid also
helps start a system in low ambients and prevents low
suction pressure and low oil differential faults by in-
creasing the load.
At ambients above 40°F, once on, the Economizer So-
lenoid will remain energized until the VSD frequency
drops below 90 Hz. Below 90 Hz, the solenoid will
be turned off, regardless of the time remaining on the
economizer timers. Under these conditions, the econo-
mizer timers will be set to "0" when the solenoids are
de-energized. Below 100 Hz, if the economizer timer
has timed out, the Economizer Solenoids will be turned
off, the unload timer will be set to 30 seconds, the
economizer timer will be set to 30 seconds if less than
30 sec.
If a motor temperature sensor exceeds 240°F, the
Economizer Solenoid will de-energize to avoid over-
heating the hot motor. When the economizer solenoid
is de-energized, the compressor unload timer is set to
30 seconds and the economizer solenoid timer is set
to 60 seconds. All other economizer timers for other
systems are set to 30 seconds, if they are already less
than 30 seconds.
The Economizer Solenoid timer prevents the solenoid
from cycling too often.
Whenever a compressor is to be turned off, all sys-
tem Economizer Solenoids will be de-energized when
the compressor(s) ramp down. The solenoids on the
compressors that will be ramped back up, if any, will
remain off for 30 seconds before the Chiller Control
Board allows the solenoids to re-energize. Once on,
the economizer solenoid(s) must remain on for 30 sec-
onds as determined by the economizer timer for each
system.
Section 7 - Operation
7
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