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Normally, air-cooled chillers such as YCAS chillers
should have the cutout set at 395 PSIG (27 bar) for R22
and R407C models. The micro will, however, accept val-
ues between 200 - 399 PSIG (14 - 28 bar). For this cutout
to be functional, the Discharge Pressure Read-out Option
must be installed (fitted as standard on 50 Hz models).
This programmable value is password protected.
To program the Discharge Pressure Cutout, key in the
desired value and press the Enter key to store the value
into memory and scroll to the next display.
High Discharge Pressure Unload Point
D I S C H A R G E
U N L O A D
=
3 6 0 . 0
The Discharge Pressure Unload point is used to avoid
a high pressure cutout shutdown by unloading a com-
pressor, if its discharge pressure approaches the cutout
value. The chiller can then continue to run automatically
at reduced capacity until the cause of the excessive pres-
sure is attended to (e.g. dirty condenser coils) or ceases
naturally (e.g. high ambient temperature).
For the first 60 seconds of operation, discharge pressure
limiting is disabled. After this time, if discharge pressure
exceeds the programmed limit, a 1 second unload pulse
will be sent to the slide valve of the affected compressor
every 5 seconds until the discharge pressure drops below
the programmed limit. The message will be removed
and reloading take place when discharge pressure has
dropped 60 PSIG (4 bar) below the threshold.
Typically the unload point should be set 20 - 25 PSIG
(1.4 - 1.7 bar) below the below the discharge pressure
cutout setting. The micro will accept a range of pro-
grammable values between 200 - 399 PSIG (14 - 28
bar). This programmable value is password protected.
To program the Discharge Pressure Unload, key in the
required setting and press the Enter key to store the value
into memory and scroll to the next display.
Low Suction Pressure Cutout
S U C T I O N
P R E S S U R E
C U T O U T
=
4 4 . 0
The Low Suction Pressure Cutout protects the evapora-
tor from damage due to ice build up caused by operation
at low refrigerant suction pressure.
JOHNSON CONTROLS
P R E S S U R E
P S I G
P S I G
After the compressor starts, and the pump down cycle
is completed (pump down to cutout or 30 seconds,
whichever comes first.), suction pressure is monitored
as long as the compressor runs. For the first 270 seconds
of running, suction pressure can be lower than the pro-
grammed cutout, but must be greater than:
Programmed
X
Cutout
Example: If programmed Cutout = 44 PSIG (3 bar)
and Run Time = 60 seconds
60/3 + 10
New Cutout = 44 X
100
This cutout value increases with time, until after 270 sec-
onds, it equals the programmed cutout value. If suction
pressure falls below the calculated cutout value before
270 seconds, the system will be shut down.
After 270 seconds, a transient timer system prevents
short term fluctuations in suction pressure from causing
shutdown as follows: If suction pressure drops below the
cutout point, a 90 second transient timer starts. During
the 90 second time period, the suction pressure must
be greater than:
Programmed
100 - transient time remaining
X
Cutout
Example:
If programmed Cutout = 44 PSIG (3 bar)
and the timer has run 30 seconds:
New Cutout = 44 PSIG X 100-60 = 17.6 PSIG (1.2 bar)
This cutout value increases with time, until after 90
seconds, it equals the programmed cutout value. If the
suction pressure rises to more than 5 PSI (0.3 bar) above
the programmed cutout value during the 90 second time
period, the timer will be reset. If the suction pressure
does not rise to more than 5 PSI (0.3 bar) above the
cutout, the timer will remain at zero and if the pressure
then falls below the cutout again, the system will shut
down on a low pressure fault.
If the Dip Switch on the microprocessor board is set
for "Water Cooling" (see Section 3.7), the cutout is
programmable between 44 - 70 PSIG (3-5 bar) for both
R22 and R-407c models. In this mode, settings of 44
PSIG (3 bar) for R22 and R-407C are recommended. If
the Switch is set for "Brine Cooling" (glycol) the cutout
is programmable between 5 - 70 PSIG (0.3 bar) for R22
and R-407c models. In this mode, the cutout should be
FORM 201.18-NM7
Run Time/3 + 10
100
= 13.2 PSIG (0.9 bar)
100
100
163
8
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