York YCAS0130 - Manual (Page 161)

161 YORK INTERNATIONAL
FORM 201.19-NM1 (204)
8
cooling mode, the saturated suction temperature unload
point is 24ºF (-4.42ºC). In glycol cooling mode, the
control is inactive. The load limiting thresholds are
shown in the following table:
Temperature Difference
Between Saturated Suc-
tion Temperature and the
Unload Temperature
Maximum Steps of
Loading After Load
Timer Counts to "0"
< 7.0 3
< 4.5 2
< 2.5 1
< 1.0 0
ANTICIPATORY UNLOADING CONTROLS
The purpose of these controls is to prevent the system
from ever reaching a point where pressure or tempera-
ture safety threshold would be exceeded shutting down
a system. This is accomplished by forcibly unloading
the compressor.
Anticipatory unloading controls monitor motor current,
discharge pressure, and saturated suction temperature
every 2 seconds and compare the values with the user
or internally programmed unload points. When the
system exceeds the unload point, the micro unloads
the compressor based upon the difference between the
actual pressure/temperature and the unload point. This
action is taken even through there may be a need for
additional cooling.
In the case of both the Motor Current and Discharge
Pressure, the micro unloads the compressor as follows
based on the user programmed unload threshold. The
amount of unloading based upon the deviation versus
the number of steps of unloading which will take place
is outlined in the following table:
Percentage of Motor
Current or Discharge
Pressure Unload Point
Maximum Steps of
Unloading After Load
Timer Counts to "0"
> 100 % 1
> 102 % 2
> 104 % 3
> 106% 4
> 108 % 5
> 115 % 10
In the case of Saturated suction temperature, the unload-
ing is based on saturated suction temperature dropping
below the internally programmed unload threshold. In
the water cooling mode, the saturated suction tempera-
ture unload point is 24ºF (-4.42ºC) In the glycol cooling
mode, the saturated suction temperature unload point is
equal to the leaving chilled liquid setpoint -11ºF (6.1ºC).
The unload limiting thresholds are shown in the table
below:
Temperature Difference
Between Saturated Suc-
tion Temperature and the
Unload Temperature
Maximum Steps of
Unloading After Load
Timer Counts to "0"
< 0.0 1
< -0.5 2
< -1.0 3
< -1.5 4
< -2.0 5
< -3.5 10
Whenever these controls are active, a STATUS Message
will appear on the display indicating the condition. See
displays below:
DISCHARGE TEMPERATURE ANTICIPATORY
SHUTDOWN CONTROL
If the discharge temperature nears the safety shutdown
point, the micro may turn off the compressor to avoid a
high discharge temperature fault.
If the discharge temperature rises above 255ºF (123ºC),
the micro will pump down the compressor and shut it off.
The micro will not allow the affected system to restart
for a period of 15 minutes. A message indicating the
compressor start inhibit will be displayed. An example
of the display is shown below:
OIL TEMPERATURE ANTICIPATORY SHUTDOWN
CONTROL
If the oil temperature nears the safety shutdown point,
the micro may turn off the compressor to avoid a high
oil temperature fault.
S Y S # D S C H L I M I T I N G
S Y S # D S C H L I M I T I N G
S Y S # C U R R L I M I T I N G
S Y S # C U R R L I M I T I N G
S Y S # S U C T L I M I T I N G
S Y S # S U C T L I M I T I N G
S Y S # D S C H / O I L I N H I B
S Y S # D S C H / O I L I N H I B