Bryant 548J*17 D Series, Installation Instructions Manual

Page: 24 / 56

24
larger than no. 18 AWG cannot be directly connected to
the thermostat and will require a junction box and splice
at the thermostat.
C
W2
G
W1
R
Y1
Typical
Thermostat
Corrections
O/B/Y2
(see Note)
Note: Typical multi-function marking. Follow manufacturer’s configuration
instructions to select Y2. Do not configure for O output.
Field Wiring
Central
Terminal
Board
W1
Y2
Y1
R
W2
G
C
X
W1
Y2
Y1
R
W2
G
C
X
T–STAT
See
Caution
UNIT DAMAGE HAZARD
Failure to follow this caution may cause a short circuit.
CAUTION
!
Carefully check the connection of control coductor
for indoor fan control at terminal G. Connecting the
indoor fan lead to terminal C will cause a short circuit
condition which can cause component damage inside
the unit or at thermostat.
C14067
Fig. 27 -- Typical Low--Voltage Control Connections
Central Terminal Board
The Central Terminal Board (CTB) is a pass through
connection point. The CTB provides the capability to add
factory--installed options and field--installed accessories to
the units by cutting jumper wires without having to change
or reroute wires through the structure of the unit. The CTB
does not provide any microprocessor control; it is simply a
basic multifunction wiring terminal configuration.
Commercial Defrost Control
The Commercial Defrost Control Board (DFB)
coordinates thermostat demands for supply fan control, 1
or 2 stage cooling, 2 stage heating, emergency heating and
defrost control with unit operating sequences. The DFB
also provides an indoor fan off delay feature (user
selectable). See Fig. 28 for board arrangement.
DIP
Switches
Speed-Up
Jumpers
C09275
Fig. 28 -- Defrost Control Board Arrangement
The DFB is located in the 548J unit’s main control box (see
Fig. 29 on page 25). All connections are factory--made
through harnesses to the unit’s CTB, to IFC (belt--drive
motor) or to ECM (direct--drive motor), reversing valve
solenoids and to defrost thermostats. Refer to Table 5 (on
page 25) for details of DFB Inputs and Outputs.
Reversing valve control — The DFB has two outputs for
unit reversing valve control. Operation of the reversing
valves is based on internal logic; this application does not
use an “O” or “B” signal to determine reversing valve
position. Reversing valves are energized during the
cooling stages and the defrost cycle and de--energized
during heating cycles. Once energized at the start of a
cooling stage, the reversing valve will remain energized
until the next heating cycle demand is received. Once
de--energized at the start of a Heating cycle, the reversing
valves will remain de--energized until the next cooling
stage is initiated.