Bryant 548J*14D Series, Installation Instructions Manual

Page: 22 / 56

22
insulated wire [35
_
C (95
_
F) minimum]. For over 75 ft.
(23 m), use no. 14 AWG insulated wire [35
_
C (95
_
F)
minimum]. All wire sizes larger than no. 18 AWG cannot
be directly connected to the thermostat and will require a
junction box and splice at the thermostat.
X
C
G
W2
C
W2
G
W1
O/B/Y2
Y2
R
W1
R
Y1 Y1
T
H
E
R
M
O
S
T
A
T
(Note 1)
(Note 2)
Note 1: Typical multi-function marking. Follow manufacturer’s configuration
instructions to select Y2. Do not configure for O output.
Note 2: W2 connection not required on units without electric heating.
Field Wiring
Central
Terminal
Board
Typical
Thermostat
Connections
C09012
Fig. 34 -- 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. 35 for board arrangement.
The DFB is located in the 548J unit’s main control box (see
Fig. 36 on page 23). 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 for
details of DFB Inputs and Outputs.
DIP
Switches
Speed-Up
Jumpers
C09275
Fig. 35 -- Defrost Control Board Arrangement
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.
Compressor control — The DFB receives inputs indicating
Stage 1 Cooling, Stage 2 Cooling and Stage 1 Heating from
the space thermostat or unit control system (RTU Open
controller); it generates commands to start compressors with
or without reversing valve operation to produce Stage 1
Cooling (one compressor runs), Stage 2 Cooling (both
compressors run) or Stage 1 Heating (both compressors run).
Auxiliary (Electric) Heat control — The 548J unit can be
equipped with one or two auxiliary electric heaters to
provide a second stage of heating. The DFB will energize
this Heating System for a Stage 2 Heating Command
(heaters operate concurrently with compressor(s) in the Stage
1 Heating cycle), for an Emergency Heating sequence
(compressors are off and only the electric heaters are
energized) and also during the Defrost cycle (to eliminate a
“cold blow” condition in the space).
Defrost —
The defrost control mode is a time/temperature
sequence. There are two time components: The
continuous run period and the test/defrost cycle period.
The temperature component is provided by Defrost
Thermostat 1 and 2 (DFT1 and DFT2) mounted on the
outdoor coil.