York MILLENIUM YCAS Series, Установка, эксплуатация и обслуживание, Страница: 138 / 156

138
YORK INTERNATIONAL
Normally, air-cooled chillers such as YCAS chillers
should have the cutout set at 27 bar (395 PSIG) for
R-22 and R-407c models. The micro will, however, ac-
cept 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
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
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 cut-
out setting. The micro will accept a range of program-
mable 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
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.
After the compressor starts, and the pump down cycle
is completed (pump down to cutout or 30 seconds, which-
ever 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:
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:
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
R-22 and R-407c models. In this mode, settings of 3
bar (44 PSIG) for R-22 and R-407c are recommended.
If the Switch is set for “Brine Cooling” (glycol) the cut-
out is programmable between 0.3 - 4.8 BARG (5 - 70
PSIG) for R-22 and R-407c models. In this mode, the
Programmed 100 - transient time remaining
Cutout 100
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)
100
S U C T I O N P R E S S U R E
C U T O U T = 3 . 0 B A R G
D I S C H A R G E P R E S S U R E
U N L O A D = 2 4 . 8 B A R G
Programmed X Run Time/3 + 10
Cutout 100
Example: If programmed Cutout = 3 bar (44 PSIG)
and Run Time = 60 seconds
60/3 + 10
100
New Cutout = 44 X = 0.9 bar (13.2 PSIG)
X
Micro Panel Contents