Installation manual

51
RCT Models, 16 Feb 2012D Roth
COMBINATION UNIT CONTROLS
The hot water (combination unit) control board
prioritizes unit operation even when there are
simultaneous calls from the thermostat and aqua-
stat. Inputs to the board include thermostat signals
as well as an aqua-stat input. The hot water board
acts as a “traffi c director,” since all inputs are sent to
the hot water board fi rst. Then, based upon priority
selection, signals are directed to the lockout board,
hot water mode outputs (pump relay, direction
valve, 3-way valve), and/or the ECM control board.
If there is a simultaneous heating and hot water call,
by default, hot water will take priority in the default
dip switch setting. Hot water priority DIP switches will
allow the choice of four priority modes (see below).
In default (hot water) mode, any time there is an
input from the aqua-stat, water heating is priority. If
there is a call from the thermostat for reversing valve
(“O”), the call will be ignored until the hot water call
has been satisfi ed. If there is a simultaneous call for
hot water and hot air (“Y1,” “G,” and “HW”), the
thermostat inputs will be ignored. An “HW” call by
itself will cause an output on “Y1C” to the lockout
board, and an output to the hot water mode
components (pump relay, direction valve, 3-way
valve) on terminal “HW.”
PRIORITY SELECTION
Priority selections are defi ned as follows:
• Hot water priority (default mode): In hot water
priority mode, the aqua-stat input always takes
priority, regardless of the thermostat inputs.
Once the hot water call is satisfi ed, and there is
still a thermostat call, the unit attempts to satisfy
the thermostat call.
• Hot water priority with electric heat: In hot
water priority with electric heat mode, the
aqua-stat input always takes priority, regardless
of the thermostat inputs. However, if there is
a simultaneous thermostat call for heating
(reversing valve is not energized), the control
will energize the fan and electric heat outputs,
allowing electric heat to satisfy the thermostat
call. Once the hot water call is satisfi ed, and
there is still a thermostat call, the unit will then
attempt to satisfy the thermostat’s force air call
after a fi ve-minute anti-short cycle time delay
(i.e. compressor). The thermostat inputs will
determine the operating mode.
• Forced air priority: In forced air priority mode, the
thermostat input always takes priority, regardless
of the aqua-stat input. Once the thermostat call
is satisfi ed, and there is still an aqua-stat call, the
unit attempts to satisfy the hot water call after a
fi ve-minute anti-short cycle time delay.
• Shared priority: In shared priority mode, the unit
operates in the hot water priority mode and
in forced air priority mode in an alternating
sequence. There is a fi eld selectable timer,
which will allow settings of 20, 30, or 40 minutes
for switch over time. The unit will always start
in hot water priority mode at the fi rst call for
hot water (aqua-stat input). Then, based upon
the timer setting, the unit will switch to forced
air priority for the selected amount of time. For
example, if the timer is set for 20 minutes, and
the unit has a simultaneous call for hot water
and thermostat, the control will operate the hot
water mode for 20 minutes and switch over to
forced air priority for 20 minutes. The unit can
switch back to hot water priority for 20 minutes,
and so on until the calls are satisfi ed. If the
aqua-stat call is satisfi ed, forced air operation is
allowed at any time; likewise if the thermostat is
satisfi ed, hot water operation is allowed at any
time. There is a fi ve-minute anti-short cycle timer
between modes.
Section 14b: Combination Unit Controls
HW HW HW Y2C W Y1F O Y1C Y2F G
REF REV PMP OUT OUT OUT OUT OUT OUT OUT
R
C
HW
Y2
Y1
G
W
O
ON
HW HW STATUS
POWER OUT IN 2 1
Combination
Board
Figure 16: Combination Unit Control Board