Central Terminal Board; Commercial Defrost Control - Carrier 50TCQD14 Installation Instructions Manual

For wire runs up to 50 ft. (15 m), use no. 18 AWG
(American Wire Gage) insulated wire (35_C minimum).
For 50 to 75 ft. (15 to 23 m), use no. 16 AWG insulated
wire (35_C minimum). For over 75 ft. (23 m), use no. 14
AWG insulated wire (35_C 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.
Typical
Thermostat
Connections
C
G
W2
(Note 2)
W1
O/B/Y2
(Note 1)
Y1
R
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
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
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.
Central
Terminal
Board
X
C
T
H
G
E
R
W2
M
O
W1
S
T
Y2
A
T
Y1
R
C09012
Control Board (DFB)
Fig. 35 - - Defrost Control Board Arrangement
The DFB is located in the 50TCQ 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.
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 (PremierLinkt
controller or 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 50TCQ 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).
22
DIP
Switches
Speed-Up
Jumpers
C09275