York Millennium YCAS Series Installation Operation & Maintenance page 169

Normally, air-cooled chillers such as YCAS chillers
should have the cutout set at 27 bar (395 PSIG) for R22
and R407c models. The micro will, however, accept
values between 14 - 28 bar (200 - 399 PSIG). For this
cutout to be functional, the Discharge Pressure Read-
out Option must be installed (fitted as standard on 50Hz
models). This programmable value is password pro-
tected.
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 =
The Discharge Pressure Unload point is used to avoid a
high pressure cutout shutdown by unloading a compres-
sor, 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 pres-
sure limiting is disabled. After this time, if discharge
pressure exceeds the programmed limit, a 1 second un-
load pulse will be sent to the slide valve of the affected
compressor every 5 seconds until the discharge pres-
sure drops below the programmed limit. The message
will be removed and reloading take place when dis-
charge pressure has dropped 4 bar (60 PSIG) below the
threshold.
Typically the unload point should be set 1.4 - 1.7 bar
(20 - 25 PSIG) below the below the discharge pressure
cutout setting. The micro will accept a range of pro-
grammable values between 14 - 28 bar (200 - 399 PSIG).
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 = 3 . 0
The Low Suction Pressure Cutout protects the evapo-
rator from damage due to ice build up caused by opera-
tion at low refrigerant suction pressure.
YORK INTERNATIONAL
P R E S S U R E
2 4 . 8 B A R G
B A R 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 sec-
onds of running, suction pressure can be lower than the
programmed cutout, but must be greater than:
Programmed X
Cutout
Example: If programmed Cutout = 3 bar (44 PSIG)
and Run Time = 60 seconds
60/3 + 10
New Cutout = 44 X
100
This cutout value increases with time, until after 270
seconds, it equals the programmed cutout value. If suc-
tion 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 caus-
ing shutdown as follows: If suction pressure drops be-
low 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 = 3 bar (44 PSIG)
and the timer has run 30 seconds:
New Cutout = 44 PSIG X 100-60 = 1.2 bar (17.6 PSIG)
This cutout value increases with time, until after 90
seconds, it equals the programmed cutout value. If the
suction pressure rises to more than 0.3 bar (5 PSI) 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 0.3 bar (5 PSI) 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 pro-
grammable between 3-5 bar (44 - 70 PSIG) for both
R22 and R-407c models. In this mode, settings of 3 bar
(44 PSIG) for R22 and R-407c are recommended. If
the Switch is set for "Brine Cooling" (glycol) the cut-
out is programmable between 0.3 bar (5 - 70 PSIG) for
R22 and R-407c models. In this mode, the cutout should
FORM 201.18-NM4
Run Time/3 + 10
100
= 0.9 bar (13.2 PSIG)
100
100
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