6
EN
General Information VARC Chiller Controls
2.2 Inputs and Outputs
The VARC allows you to monitor analog inputs, digital inputs, and relay outputs to determine the status of the system.
2.2.1 Analog Inputs
I
If a temperature sensor is defective or not connected, the VARC generates an alarm for that sensor.
Input I/O #
Board
I/O
Description
Chilled Water Return
Temperature Sensor
AI-1 B1 The chilled water supply sensor is continuously monitored whether in Cooling, Reverse Cycle,
or Electric Heat mode. It detects a high-temperature condition in the supply water from the
chiller. If the chilled water temperature is greater than or equal to 125°F (52°C), the following
occurs:
• In Reverse Cycle mode, all enabled compressor relays are de-energized, turning off the
compressors.
• In Electric Heating mode, all enabled heater relays are de-energized, turning off the
heating elements.
• A high temperature fault is generated.
• The compressor or electric heat relay re-energizes when the temperature drops to 110°F
(43°C).
You must acknowledge and clear the fault prior to re-enabling the VARC or the disabled
stage. See “Viewing Alarms for Each Stage” on page 28.
Freeze Temperature
Setpoint
AI-2 B2 The chilled water supply sensor is continuously monitored whether in Cooling, Reverse Cycle,
or Electric Heat mode. It detects a freeze condition in the supply water of the chiller. If the
chilled water temperature is equal to or less than 36°F (2°C), the following occurs:
• The compressor relay is de-energized, shutting off the compressor.
• A low temperature fault is generated.
• The compressor relay re-energizes when the temperature reaches 42°F (6°C).
You must acknowledge and clear the fault prior to re-enabling the VARC or the disabled
stage. See “Viewing Alarms for Each Stage” on page 28.
Condenser Freeze
Protection
AI-3 B3 The condenser outlet refrigerant temperature sensor monitors the condenser coil
temperature. In Heat mode, if the coil temperature drops below 30°F (-1°C), the VARC
automatically lowers the speed of the compressor to half the speed that it was currently
running. While performing this operation, the display indicates Freeze Defrost.
Suction Pressure
1
AI-6 B6 The VARC continuously monitors the suction pressure. If the suction pressure is below the
alarm setpoint for longer than the programmed time delay, a Low Suction Pressure fault is
generated.
You must acknowledge and clear the fault prior to re-enabling the VARC or the disabled stage
See “Viewing Alarms for Each Stage” on page 28.
Discharge Pressure
1
AI-7 B7 The VARC continuously monitors the discharge pressure. If the discharge pressure is above
the alarm setpoint for longer than the programmed time, a High Discharge Pressure fault is
generated.
You must acknowledge and clear the fault prior to re-enabling the VARC or the disabled
stage. See “Viewing Alarms for Each Stage” on page 28.
Pump Current
Monitoring
(Optional)
1
AI-9
(CW)
AI-10
(SW)
B-9 (CW)
B-10 (SW)
Pump current monitoring for the chilled water and Sea Water Pump (SWP) is an optional
feature. It requires the medium-sized PLC, instead of the standard smaller version. With this
option, you can view the current draw from each pump on the PGD1 display and the touch
screen.
1
The VARC has a proprietary algorithm that keeps the system from turning off immediately for low pressure or high pressure. The VARC gradually reduces its speed
to compensate for low or high pressure conditions.
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