111
Factory-Installed Components
MAIN BASE BOARD (MBB)
See Fig 30. The MBB is the center of the ComfortLink control
system. The MBB contains the major portion of the operating
software and controls the operation of the unit. The MBB has
22 inputs and 11 outputs. See Table 100 for the inputs and out-
put assignments. The MBB also continuously monitors addi-
tional data from the optional ECB1, ECB2, SCB, SCB2, EXV,
and CEM boards through the LEN communications port. The
MBB also interfaces with the Carrier Comfort Network
®
sys-
tem through the CCN communications port. The board is locat-
ed in the main control box.
ECONOMIZER BOARD (ECB1)
The ECB1 controls the economizer actuator and the power ex-
haust fans. The ECB1 operates the economizer motor using a
digital communication signal that also provides status and di-
agnostics for the economizer motor. See Fig. 31. The ECB1
also controls the operation of the power exhaust motors and
provides up to 6 stages of digitally sequenced power exhaust
either based on the economizer motor position or the building
pressure. The board has 4 inputs and 6 outputs. Additionally,
ECB1 provides an output that will send a 4 to 20 mA signal to
a field-installed VFD power exhaust accessory. Details can be
found in Table 101. The ECB1 board is located in an auxiliary
box located at the end of the unit behind the filter access door.
The board also contains a second LEN port than can be used
with the accessory Navigator™ display.
VAV BOARD (ECB2)
The VAV board (which is the same hardware as the ECB1) is
used to control the supply fan on VAV units. See Fig. 31. It
sends a 4 to 20 mA signal to the VFD based on a supply duct
pressure sensor connected to the board. The board also accepts
a signal from another pressure sensor that monitors building
pressure and controls the operation of the optional modulating
power exhaust motors. The board will also be used on CV units
with the optional building pressure control feature and modu-
lating power exhaust. This board is also used to control a digi-
tally controlled hot gas bypass solenoid with an integral orifice
for use in low load applications. This board is located in the
auxiliary control box. Input and output assignments are sum-
marized in Table 102.
STAGED GAS HEAT BOARD (SCB)
When optional staged gas heat is used on CV and VAV units, the
SCB board is installed and controls operation of the gas valves.
See Fig. 32. The SCB also provides additional sensors for moni-
toring of the supply-air temperature. This board is located in the
gas heat section of the unit. The inputs and outputs are summa-
rized in Table 103.
ROOFTOP CONTROL BOARD (RXB)
The RXB is used in place of ECB2 on all unit sizes with op-
tional digital scroll compressor and or optional Humidi-MiZer
system. The board has additional inputs to sense the digital
compressor discharge temperature. The board has additional
outputs to control digital scroll modulation. This board is locat-
ed in the auxiliary control box. Input and output assignments
are summarized in Table 104.
CONTROL EXPANSION MODULE (CEM)
The optional CEM (also available as an accessory) is used to
accept inputs for additional sensors or control sequence switch-
es, including:
• smoke control mode field switches
• VAV supply air temperature setpoint reset using an exter-
nal 4 to 20 mA signal
• outdoor air CO
2
sensor (for supply duct pressure reset us-
ing an eternal 4 to 20 mA signal)
• external fan status pressure switch input (CV units)
• demand limit sequence proportional signal or discrete
switches
The CEM board is located in the main control box. See Fig. 33.
The inputs and outputs are summarized in Table 105.
COMPRESSOR PROTECTION CURRENT SENSOR
BOARD (CSB)
This board monitors the status of the compressor by sensing
the current flow to the compressors and then provides digital
status signal to the MBB.
EXPANSION VALVE CONTROL BOARD (EXV)
The EXV is used on Humidi-MiZer
®
equipped units only. It is
used to provide control of the condenser and bypass modulat-
ing valves, as well as having additional inputs to sense the
evaporative discharge temperature. See Fig. 34 and Table 106.
INTEGRATED GAS CONTROL (IGC)
One IGC is provided with each bank of gas heat exchangers (2
used on the size 020-050 units and 3 on size 060 units). The
IGC controls the direct spark ignition system and monitors the
rollout switch, limit switches, and induced-draft motor Hall Ef-
fect switch. The IGC is equipped with an LED (light-emitting
diode) for diagnostics. See Table 107.
LOW AMBIENT SCREW COMPRESSOR BOARD (SCB2)
The SCB2 is used on optional low ambient Motormaster
®
equipped units only. It is used to provide control of the VFD to
the condenser fans.
PHASE LOSS PROTECTION MONITOR OPTION (PLP)
If all 3 phases of electrical supply are relatively equal and in
proper sequence, the normally open contacts (Y/Y-OUT) will
close when 24 volts is applied between C and Y terminals. If
the phases are out of sequence, or if one is missing, the con-
tacts will never close. If a phase is lost while the phase monitor
is energized, the contacts will open immediately and will re-
main open until the error is corrected.
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