82
48/50HC 17-28 Units — Low Voltage Terminal
Boards (TB A and TB B)
There are two terminal boards with 16 terminals each, and ori-
ented one mounted above the other. The front have screw ter-
minals and the back have spade connectors. These terminal
boards provide a connection point for the thermostat or space
sensor and for most field-installed accessories. See Table 33.
Communication Interface Board (CIB)
This circuit board provides a field connection point for unit
communications. The Local Equipment Network (LEN) RJ-11
connector allows a hand-held Navigator to be plugged in to ac-
cess the unit’s menus. The Carrier Comfort Network
®
(CCN)
RJ-11 connector or the CCN screw terminals allow building
communication connections. See Fig. 35.
Fig. 35 — Communications Interface Board (CIB)
Central Terminal Board (CTB)
This circuit board is a simple trace board that serves as a junc-
tion point between components and the ComfortLink system. It
is the distribution center for transformer 1’s power. The inte-
grated gas controller (IGC), electric heater control, compressor
control, and unit shutdown all feed through this trace board.
See Fig. 36 and Table 34 for the connections through this
board.
Fig. 36 — Central Terminal Board (CTB)
*Point name displayed on the scrolling marquee or Navigator™ display.
1
2
3
4
LEN CCN
CCN
(+) (-)(com) shield
Table 33 — Upper and Lower Field Connection Terminal (TB A and TB B) Board Connections (17-28 Size Units)
TERMINAL
BLOCK
TERMINAL
LABEL
DISPLAY
NAME*
DESCRIPTION
SENSOR
LOCATION
TYPE OF I/O
TERMINAL
NUMBER
Upper
(TB A)
C- 2 Transformer 2 Common 24 VAC common 1,3,4
R- 2 24 VAC power Transformer 2 24 VAC 13,15,16
SPT+ SPT Space temperature (T55/56) space 10k thermistor 8
SPT- SPT Space temperature (T55/56) space 10k thermistor 7
SPTO SPTO Space temperature offset (T56) space 10k thermistor 5
FDWN FDWN Fire shutdown switch input
supply/return/
space
24 VAC input 11
X ALRM Alarm output (normally open) space 24 VAC output 2
G G Thermostat G (Fan) space 24 VAC input 6
W1 W1 Thermostat W1 (1st stage heat) space 24 VAC input 8
W2 W2 Thermostat W2 (2nd stage heat) space 24 VAC input 10
Y1 Y1 Thermostat Y1 (1st stage cool) space 24 VAC input 12
Y2 Y2 Thermostat Y2 (2nd stage cool) space 24 VAC input 14
Lower
(TB B)
RAT RAT Return Air Temperature Sensor return duct 10k thermistor 1,3
SAT SAT Supply Air Temperature Sensor Blower or duct 10k thermistor 5,7
HUM HUM Humidistat switch input
supply/return/
space
switch input 9
LPWR
Analog Sensor Loop power
(24vdc)
24 VDC 8
COM Analog sensor common Ground 4
IAQ IAQ Indoor air quality sensor return/space 4- 20 mA input 6
SPRH SP.RH or OAQ
Relative humidity sensor or
Outdoor air quality sensor
field installed 4-20 mA input 2
RMOC RM.OC Remote occupancy switch field installed 24 VAC input 10
ENTH ENTH or IAQ.S
Outdoor enthalpy switch, or
Indoor air quality switch
economizer, or
return/space
24 VAC input 12
R- 2 24 VAC power Transformer 2 24 VAC 15
C- 2 Transformer 2 Common 24 VAC common 16
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