Carrier AQUAFORCE 30XW150-400 User Manual

Page 44

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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 Satu-

rated 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.

Table 33 — Capacity Control Overrides

CAPACITY CONTROL OVERRIDES

Cooler Freeze Protection

Circuit A Low Saturated Suction Temperature in Cooling

Circuit B Low Saturated Suction Temperature in Cooling

—

Low Temperature cooling and High Temperature Heating (LWT)

Low Temperature cooling and High Temperature Heating (EWT)

Ramp Loading

Service Manual Test Override

Demand Limit

Cooler Interlock Override

High Temperature Cooling and Low Temperature Heating

High Temperature Cooling and Low Temperature Heating
(minimum load control in effect)

Minimum On/Off and Off/On Time Delay

Slow Change Override

System Manager Capacity Control

Circuit A High Pressure Override

Circuit B High Pressure Override

—

Standby Mode

—

Minimum On Time Delay

Circuit A Low Saturated Suction Temperature in Cooling

Circuit B Low Saturated Suction Temperature in Cooling

—

Circuit A Low Refrigerant Charge

Circuit B Low Refrigerant Charge

—

Circuit A High Current Override

Circuit B High Current Override

—

Circuit A High Suction Superheat at Part Load

Circuit B High Suction Superheat at Part Load

—

Circuit A Delay for Unloading the Slide Valve

Circuit B Delay for Unloading the Slide Valve

—

Circuit A Low Oil Level

Circuit B Low Oil Level

—

Circuit A High Motor Temperature Override

Circuit B High Motor Temperature Override

—

Circuit A High Discharge Gas Override

Circuit B High Discharge Gas Override

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