Specifications

44
Capacity Control Overrides — The following ca-
pacity control overrides (Active Capacity Override, CAP.S)
will modify the normal operation routine. If any of the override
conditions listed below are satisfied, the override will deter-
mine the capacity change instead of the normal control. Over-
rides are listed by priority order and are often linked to unit op-
erating modes. See Table 34 for a list of overrides. See the Op-
erating Modes section on page 58 for more information
regarding operating modes.
Override #1: Cooler Freeze Protection
— This override at-
tempts to avoid the freeze protection alarm. If the Leaving
Water Temperature is less than Brine Freeze Set Point (Brine
Freeze Setpoint, LOSP) + 2.0° F (1.1º C) then a stage of
capacity is removed.
NOTE: The freeze set point is 34 F (1.1 C) for fresh water
systems (Cooler Fluid Type, FLUD=1). The freeze set point
is Brine Freeze Set Point (Brine Freeze Setpoint, LOSP), for
Medium Temperature Brine systems (Cooler Fluid Type,
FLUD=2).
Override #2: Circuit A Low Saturated Suction Temperature
in Cooling
Override #3: Circuit B Low Saturated Suction Temperature
in Cooling — These overrides attempt to avoid the low suction
temperature alarms and are active only when the compressor is
running beyond the fully unloaded level. The slide valve in the
affected circuit will be decreased in position if the Saturated
Suction Temperature is less than Brine Freeze Set Point (Brine
Freeze Setpoint, LOSP) –18.0 F (–10 C) for 90 seconds, or the
Saturated Suction Temperature is less than –4 F (–20 C).
Override #5: Low Temperature Cooling and High Tempera-
ture Heating — This override decreases capacity when the dif-
ference between the Control Point (Control Point, CTPT) and
the Leaving Water Temperature (Cooler Leaving Fluid, LWT)
reaches a predetermined limit and the rate of change of the wa-
ter is 0º F per minute or still decreasing.
Override #6: Low Temperature Cooling and High Temperature
Heating — This override decreases capacity (approximately
5% of circuit capacity) when the Entering Water Temperature
(Cooler Entering Fluid, EWT) is less than the Control Point
(Control Point, CTPT).
Override #7: Ramp Loading
— No capacity stage increase
will be made if the unit is configured for ramp loading (Ramp
Loading Select, RL.S=ENBL) and the difference between the
Leaving Water Temperature and the Control Point is greater
than 4º F (2.2º C) and the rate of change of the leaving water is
greater than Cool Ramp Loading Rate (Cooling Ramp Load-
ing, CRMP). Operating mode 5 (MD05) will be in effect.
Override #8: Service Manual Test Override
— This over-
ride mode indicates the unit has been placed into Service Test
mode. The user can then use Service Test functions to test the
unit. All safeties and higher priority overrides are monitored
and acted upon.
NOTE: The user cannot activate this override mode.
Override # 9: Demand Limit
— This override mode is active
when a command to limit the capacity is received. If the
current unit capacity is greater than the active capacity limit
value, a stage is removed. If the current capacity is lower than
the capacity limit value, the control will not add a stage that
will result in the new capacity being greater then the capacity
limit value. Operating mode 4 (MD04) will be in effect.
Override #10: Cooler Interlock Override
— This override
prohibits compressor operation until the Cooler Interlock
(Cooler Flow Switch, LOCK) is closed.
Override #11: High Temperature Cooling and Low Temper-
ature Heating — This override algorithm runs once when the
unit is switched to ON. If the difference between the Leaving
Water Temperature (Cooler Leaving Fluid, LWT) and the
Control Point (Control Point, CTPT) exceeds a calculated
value and the rate of change of the water temperature is greater
than –0.1º F/min, a stage will be added.
Override #12: High Temperature Cooling and Low Temper-
ature Heating — This override runs only when Minimum
Load Control is Enabled, (Hot Gas Bypass Select, HGBP)
and is set to 1, 2 or 3. This override will add a stage of capacity
if the next stage is Minimum Load Control, when the differ-
ence between the Leaving Water Temperature (Cooler Leav-
ing Fluid, LWT) and the Control Point (Control Point, CTPT)
exceeds a calculated value and the rate of change of the water
temperature is greater than a fixed value.
Override #13: Minimum On/Off and Off/On Time Delay
—
Whenever a capacity change has been made, the control will
remain at this capacity stage for the next 90 seconds. During
this time, no capacity control algorithm calculations will be
made. If the capacity step is a compressor, an additional
90-second delay is added to the previous hold time (see Over-
ride #22). This override allows the system to stabilize before
another capacity stage is added or removed. If a condition of a
higher priority override occurs, the higher priority override will
take precedence. Operating Mode 10 (MD10) will be in effect.
Override #14: Slow Change Override
— This override pre-
vents compressor stage changes when the leaving temperature
is close to the control point and slowly moving towards it.
Override #15: System Manager Capacity Control
— If a
Chillervisor module is controlling the unit and multiple chill-
ers, the unit will increase capacity to attempt to load to the de-
mand limited value.
Override #16: Circuit A High Pressure Override
Override #17: Circuit B High Pressure Override — This
override attempts to avoid a high pressure failure. The algo-
rithm is run every 4 seconds. If the Saturated Condensing Tem-
perature for the circuit is above the High Pressure Threshold
(High Pressure Threshold, HP.TH) then the position of slide
valve will be unloaded.
Override #19: Standby Mode
— This override algorithm will
not allow a compressor to run if the unit is in Standby mode,
(Heat/Cool Status, HC.ST=2).
DESCRIPTION STATUS POINT
Alarm Routing 0 0 0 0 0 0 0 0 ALRM_CNT
ComfortView™, or ComfortWorks
TeLink
Unused
BacLink or DataLink™
Unused
®
Fig. 26 — Alarm Routing Control
a30-4485