26
C09276
Fig. 34 − Defrost Control Board Location
Table 8 – 50TCQ Defrost Board I/O and Jumper Configurations
Inputs
Point Name Type of I/O Connection Pin Number Unit Connection Note
G Fan DI, 24Vac P2-3 LCTB-G
Y1 Cool 1 DI, 24Vac P2-5 LCTB-Y1
Y2 Cool 2 DI, 24Vac P2-4 LCTB-Y2
W1 Heat 1 DI, 24Vac P2-7 LCTB-W1
W2 Heat 2 DI, 24Vac P2-6 LCTB-W2
R Power 24Vac P3-1 CONTL BRD-8
C Common 24Vac P3-2 CONTL BRD-4
DFT1 DI, 24Vac DFT-1 to DFT-1
DFT 2 DI, 24Vac DFT-2 to DFT-2
Outputs
Point Name Type of I/O Connection Pin Number Unit Connection Note
IFO Fan On DO, 24Vac P3-9 REHEAT-2
OF OD Fan On DO, 24Vac OF OFR
RVS1 DO, 24Vac P3-7 to P3-5 Energize in COOL
RVS2 DO, 24Vac P3-6 to P3-4 Energize in COOL
COMP 1 DO, 24Vac P3-10 FPT - REHEAT-6
COMP 2 DO, 24Vac P3-8 REHEAT-8
HEAT 2 DO, 24Vac E-HEAT HC-1 (TB4-1)
COM 24Vac P3-3 HC-1 (TB4-3)
Configuration
Point Name Type of I/O Connection Pin Number Unit Connection Note
Select Jumper 24Vac P1-1
2 Compressor 24Vac P1-3 Use for 50TCQD
Speed−Up Configuration
Point Name Type of I/O Connection Pin Number Unit Connection Note
Speed-Up Jumper JMP17
Speed-Up Jumper JMP18
Jumper for 1−3 seconds: Factory Test, defrost runs for 9 seconds
Jumper for 5−20 seconds: Forced Defrost, defrost runs for 30 seconds if DFT2 is open
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 (sizes 08 −
14) and Stage 1 Heating from the space thermostat or unit
control system (PremierLink® or RTU−OPEN); it
generates commands to start compressors with or without
reversing valve operation to produce Stage 1 Cooling (one
compressor), Stage 2 Cooling (both compressors run) or
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