Dometic VARC 48, Operation Manual

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5
GENERAL
The VARC chiller is a PLC based control system that uses a PID control loop to manage the capacity requirements of the system.
This control loop allows for finite control to match the capacity of the chiller to the thermal load demand on the system. Th is system
differs greatly from the on/off control of a standard chiller system, as it will modulate the speed of the compressor to increase or
decrease its capacity allowing for reduced current consumption by the electrical system.
The chiller system will come programmed from the factory with the options enabled for that system. Although the system offers
flexibility, these options can only be enabled by a factory representative.
The user will be able to select between Normal, Econo and Boost mode operation in single stage configuration. In a multistage
configuration the user will also be able to select between Normal or Accelerated startup to bring the system chilled water temperature
down faster or in the case of heat mode temperature higher.
The VARC controller is internally grounded with isolation between inputs and outputs. Additionally, the output relays offer double
isolation so that different voltages can be used for groups of relays.
The system will utilize various sensor types for measuring analog temperatures and pressures. For temperature measurements, the
system will use NTC type 10K@77° thermistors. Pressure transducers are ratiometric 0-650 PSI (45 bar) range for both suction and
discharge monitoring.
DIGITAL INPUTS
Digital inputs are used to monitor the status of the protection circuits for the system.
Safety Inputs
All discrete inputs will be checked before the system will be enabled. Any faults detected on start-up must be verified and cleared
via the VARC before system will start normal operation.
Chilled Water Flow Switch
With the system in either heating or cooling mode the Flow switch must be closed prior to system starting or a stage being enabled.
In operation if Flow is lost for more than 10 consecutive seconds, the compressor or heat relay will be disabled. A flow switch fault
will be recorded and displayed.
A CW Flow fault will be recorded and system will be in lockout and a manual restart will be required. The VARC will not allow the
compressor or electric heat relay to be energized for the stage that has lost flow or the whole system if a common flow switch is being
used.
Fault must be manually acknowledged via the VARC and cleared prior to re-enabling the system or stage.
Refrigerant High Side Pressure Limit
The VARC will immediately acknowledge an open circuit if the HI pressure switch is tripped and de-energize the compressor. It will
record and display high pressure fault on the alarm screen. If the VARC detects a high pressure fault during operation, a HP fault will be
displayed and recorded. The VARC will not allow the compressor relay to be re-energized, until switch is in the closed position.
The fault must be manually acknowledged via the VARC and cleared prior to re-enabling the system or stage.
ANALOG INPUTS
High Limit Temperature Setpoint
The high limit temperature sensor is continuously monitored whether in Cooling, Reverse Cycle or Electric Heat mode.
This sensor is used to detect a high temperature condition in the supply water from the chiller. If the chilled water temperature is sensed
to be greater or equal to 125°F (51.7°C), all enabled compressor relays will be de-energized, turning off the compressor(s) if operating
in reverse cycle mode. If electric heat is being used, all enabled heater relays will be de-energized, turning off the heating element(s).