Ddc Controls • Introduction Ddc Features; Overview; System Inputs - Dometic DDC Operation Manual

DDC Controls • Introduction
DDC Features
DDC software revision A32 (or newer) supports
PCB-270 OOP (or newer) with the following up-grades:
• Multi-layer PC board for improved noise immunity.
• SMT (surface mount technology) reduces component
size and frees up space for hardware improvements.
• New AC Voltmeter (± 2 volt accuracy) for brownout
protection.
• Low Freon Pressure Failsafe locks out after four (4)
consecutive faults.
• Pilot duty relays for compressor and heater outputs
when the load requires contactors.
• "Euro signal terminals" eases wiring and reduces board
space requirement.
• User-friendly push button programming interface
replaces the trim pots and allows parameter viewing
without disrupting settings.
• Universal 115/220-volt switch mode power supply
eliminates large AC transformer, requires less board
space and improves 115-volt brownout operation.
• Independent Freeze-Stat and High-Pressure failsafe
hardware for protection during Bimini Jumper operation.

Overview

The DDC Module is designed for use with single or
multiple stage modular chiller assemblies to provide
hot or cold water to air handlers while maintaining
circulating water temperature at desired setpoint. The
display alternates between the return and supply water
temperatures unless a fault is detected or one of the
settings is being adjusted. The circuit board includes the
following inputs and outputs:

System Inputs

1. Mode Switch
The mode switch (DDC remote switch is sold separately)
allows heating, cooling or off mode to be selected.
Cooling Mode - The compressor will turn on when the
return water temperature is two or more degrees
(2°F/1.1°C) above the setpoint and will turn off when the
water temperature is equal or below the cooling setpoint.
Heating Mode - In heating the compressor and reversing
valve will be turned on when the water temperature falls
two degrees (2°F/1.1°C) below the heating setpoint unless
L-2281 Introduction
the system is programmed for electric heat. When electric
heat is selected the heater pilot relay and valve relay are
turned on and the compressor remains off. The compressor
or heater will be turned off when the return water is equal
to or above the heating setpoint.
Off Mode - All outputs are turned off. The power indicator
LED will remain on when the AC power to the board is on.
2. High Freon Pressure Switch
High Freon pressure fault HiP is indicated in the display
during a cooling cycle. The compressor shuts down for a
minimum time equal to its staging delay or until the fault is
cleared. The compressor will automatically restart. However,
after the fourth failure within a single cooling cycle the
compressor will lockout. To clear the lockout condition turn
the mode switch to off then back to cool or heat mode.
During the the compressor shuts down and
heat mode
restarts after the time delay but does not lockout and HiP
is not indicated.
3. Optional Low Freon Pressure Switch
When the system is equipped with a low Freon pressure
switch, low Freon pressure detection should be enabled
(see section "Program Low Freon Pressure Detection").
The LoP low Freon pressure fault is displayed if the switch
opens and remains open for more than ten (10) minutes
while the compressor is running. The LoP fault will shut
down the compressor for a minimum time equal to the
compressor staging delay or until the fault is cleared. The
compressor will automatically restart. However, after the
fourth failure within a single cooling cycle the compressor
will lockout. To clear the lockout condition turn the mode
switch to off then back to cool or heat mode.
4. Flow Switch
Detects circulating water failure if the flow switch remains
open for ten (10) seconds. This fault shuts down the
compressor for a minimum time equal to the staging delay
and FLO is shown in the display. The compressor will
restart after the staging delay and the flow fault is cleared.
5. Return Water Sensor
This sensor is required for proper operation. The heating
or cooling cycle requirement is based on return water
temperature. Should the sensor become shorted or open a
Sen sensor fault is displayed and the system shuts down
until the problem is corrected.
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