Carrier 38APS025 - Aux Board (Aux); Compressor Expansion Module (Cxb); Main Base Board (Mbb); Switch Number;Position

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the thermostat contacts and other status switches. See Table 6.
The MBB also controls several outputs. Information is trans-
mitted between modules via a 3-wire communication bus or
LEN. The CCN (Carrier Comfort Network
®
) bus is also sup-
ported. Connections to both LEN and CCN buses are made at
the LVT (low voltage terminal) terminal strip.
The Instance Jumper must be on “1.”
AUX BOARD (AUX) — This control board is used with
both the digital compressor and low ambient head pressure
control factory-installed option or field-installed accessory.
For the digital compressor option, it provides the additional in-
put for the discharge temperature thermistor (DTT) as well as
the output for the digital compressor unloader solenoid. For the
load ambient head pressure control option/accessory it pro-
vides the analog signal to the head pressure control device for
fan speed determination. See Fig. 20.
Addressing
— The board address is set by the DIP switch S1
as follows:
COMPRESSOR EXPANSION MODULE (CXB) — The
CXB is used only on unit sizes 070-130 to provide additional
inputs and outputs for fans and compressors when the unit has
more than 4 compressors. Additionally, if required refrigerant
control for the second solenoid per circuit is provided from the
CXB, a field-supplied 24-volt transformer to power the sole-
noids is required. See Fig. 21.
Addressing
— The board address is set by the DIP switch S1
as follows:
SWITCH NUMBER/POSITION
12345678
OFF ON OFF OFF ON OFF ON OFF
SWITCH NUMBER/POSITION
1234
ON ON ON ON
CEPL130346-01
STATUS
LEN
J1
J2
J4
J3
J5
J6
J7
J8
J9
J10
CCN
RED LED - STATUS GREEN LED -
LEN (LOCAL EQUIPMENT NETWORK)
YELLOW LED -
CCN (CARRIER COMFORT NETWORK)
INSTANCE JUMPER
K11
K10 K9
K8
K7
K6
K5
K4
K3 K2
K1
Fig. 19 — Main Base Board