Major System Components; General; Factory-Installed Components - Carrier Weathermaster 48P030-100 Controls, Start-Up, Operation, Service, And Troubleshooting

MAJOR SYSTEM COMPONENTS

General

The 48/50P Series package rooftop units with electric cooling and
with gas heating (48P units) or electric cooling and electric or hy-
dronic heating (50P units) contain the ComfortLink electronic
control system that monitors all operations of the rooftop. The
control system is composed of several components as listed below.
See Fig. 18-27 for typical control and power component schemat-
ics. Figures 28-30 show the layout of the control box.

Factory-Installed Components

MAIN BASE BOARD (MBB)
The MBB is the center of the ComfortLink control system. See
Fig 31. The MBB contains the major portion of the operating soft-
ware and controls the operation of the unit. The MBB has 22 in-
puts and 11 outputs. See Table 107 for the inputs and output as-
signments. The MBB also continuously monitors additional data
from the EXB, RXB, SCB, and CEM boards through the LEN
communications port. The MBB also communicates with and
controls the actuator motors, economizer, power exhaust dampers,
VFDs, IGVs, hydronic valves, and humidifier valves. The MBB
also interfaces with the Carrier Comfort Network
the CCN communications port located on the COMM3 board.
The COMM3 board has permanent terminals as well as a J11 jack
for temporary connections. The board is located in the main con-
trol box.
ROOFTOP CONTROL BOARD (RXB)
The RXB has additional inputs and outputs required for the con-
trol of the unit. All units have an RXB board. See Fig. 32. The
board has 9 inputs and 8 outputs. Details can be found in
Table 108. The RXB board is located in the main control box.
ECONOMIZER CONTROL BOARD (EXB)
The EXB is used on units with optional return fan, optional digital
scroll compressor, or accessory humidifier. See Fig. 32. The board
has inputs to sense the return fan cfm and supply fan cfm. This
board is located in the main control box. Input and output assign-
ments are summarized in Table 109.
STAGED GAS HEAT BOARD (SCB)
When optional staged or modulating gas heat is used, the SCB
board is installed and controls additional stages of gas heat. See
Fig. 33. The SCB also provides additional sensors for monitoring
of the supply-air and limit switch temperatures. For units equipped
with modulating gas heat, the SCB provides the 4 to 20 mA signal
to the SC30 board that sets the modulating gas section capacity.
This board is located in the main unit control box. The inputs and
outputs are summarized in Table 110.
CONTROL EXPANSION MODULE (CEM)
The optional CEM is used to provide inputs for demand limiting,
remote set point, and other optional inputs typically needed for en-
ergy management systems. See Fig. 34. On CCN systems, these
inputs can be interfaced through the CCN communications. It is
located in the main control box. The CEM has inputs for accesso-
ry relative humidity sensors. This board is also used on units
equipped with optional outdoor air CFM monitoring. The inputs
and outputs are summarized in Table 111.
The optional (or accessory) CEM is used to accept inputs for addi-
tional sensors or control sequence switches, including:
• Smoke control mode field switches.
• VAV supply air set point reset using an external 4 to 20 mA
signal.
• Outdoor air CO
• Space, return and/or outdoor air relative humidity sensors.
• IAQ function discrete switch.
• Demand limit sequence proportional signals or discrete
switches.
The CEM is factory-installed when the outdoor air cfm control op-
tion is installed.
COMPRESSOR EXPANSION BOARD (CXB)
The CXB is used on size 090 and 100 units only to provide addi-
tional compressor outputs and CSB inputs. See Table 112.
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 modulating valves.
See Table 113.
LOW VOLTAGE TERMINAL STRIP
This circuit board provides a connection point between the ma-
jor control boards and a majority of the field-installed accesso-
ries. See Table 114. The circuit breakers for the low voltage con-
trol transformers, interface connection for the Carrier Comfort
® system through
Network
the Local Equipment Network (LEN) communication are also
located on the low voltage terminal strip.
INTEGRATED GAS CONTROL (IGC)
One IGC is provided with each bank of gas heat exchangers. One
is used on low heat size 030-050 units. Two are used on high heat
size 030-050 units and low heat 055-100 units. Three are used on
high heat 055-100 units. The IGC controls the direct spark ignition
system and monitors the rollout switch, limit switches, and in-
duced-draft motor Hall Effect switch.
For units equipped with Modulating Gas heat, the IGC in the
Modulating Gas section uses a Pressure Switch in place of the
Hall Effect sensor. The IGC is equipped with a LED (light-emit-
ting diode) for diagnostics. See Table 115.
CURRENT SENSOR BOARD (CSB)
This board monitors the status of the compressor by sensing the
current flow to the compressors and then providing digital status
signal to the MBB and CXB.
TIMER RELAY CONTROL BOARD (TR1)
The TR1 is used on modulating gas heat equipped units only. It is
located in the Gas Heat section and is used in combination with
the SC30 to provide control of the Modulating Gas Heat section.
The TR1 receives an input from the IGC, initiates a start-up se-
quence, powers the SC30, sets the induced-draft motor speed, and
provides the main gas valve high fire input. When the start-up se-
quence is complete, the TR1 checks the input from the SC30 to
determine which state to command the induced-draft motor and
main gas valve. See Table 116.
SIGNAL CONDITIONER CONTROL BOARD (SC30)
The SC30 is used on modulating gas heat equipped units only. It is
located in the Gas Heat section and is used in combination with
the TR1 to provide control of the Modulating Gas Heat section.
The SC30 is powered by an output from the TR1. It receives a ca-
pacity input from the SCB, provides a capacity output to the mod-
ulating gas valve, and provides an output to the TR1 to determine
which state to command the induced-draft motor and main gas
valve. See Table 117.
133
sensor.
2
® (CCN) communication, and interface connection for