York MILLENNIUM YCAS, Installation Operation & Maintenance

Page: 136 / 152

136 YORK INTERNATIONAL
8.2 PROGRAM KEY -
USER PROGRAMMABLE VALUES
High Discharge Pressure Cut-Out
The Discharge Pressure Cutout is a microprocessor
backup for the mechanical high pressure cutout located
in each refrigerant circuit. This safety is bypassed for the
first 5 seconds of operation after which if the cutout point
is exceeded for 3 seconds, the system will shut down.
Normally, air-cooled chillers such as YCAS chillers should
have the cutout set at 27 bar (395 PSIG) for R22 and
R-407C 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 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 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
4 bar (60 PSIG) below the threshold.
Typically the unload point should be set 1.4 to 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
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 causing
shutdown as follows: If suction pressure drops below
the cutout point, a 90 second transient timer starts. Dur-
ing the 90 second time period, the suction pressure must
be greater than:
Programmed
x
Run Time / 3 + 10
Cutout 100
Example: If Programmed Cutout = 3 bar (44PSIG)
and Run Time = 60 seconds
New Cutout = 3 x
60/3 + 10
= 0.9 bar (13PSIG)
100
D I S C H A R G E P R E S S U R E
C U T O U T = 2 7 . 2 B A R
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
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
Programmed
x
100 – transient time remaining
Cutout 100
Example: If Programmed Cutout = 3 bar (44PSIG)
and timer has run 30 seconds.
New Cutout = 3 x
100 – 60
= 1.2 bar (17.6PSIG)
100
Micropanel