Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 160

To connect the unit to the network:
1. Turn off power to the control box.
2. Cut the CCN wire and strip the ends of the red (+), white
(ground), and black (–) conductors. (Substitute appropriate
colors for different colored cables.)
3. Connect the red wire to (+) terminal on the COMM board,
the white wire to COM terminal on the COMM board, and
the black wire to the (-) terminal on the COMM board.
4. The RJ14 CCN connector on the COMM board can also
be used, but is only intended for temporary connection (for
example, a laptop computer running Service Tool).
Restore power to unit.
IMPORTANT: A shorted CCN bus cable will prevent some
routines from running and may prevent the unit from starting.
If abnormal conditions occur, unplug the connector. If condi-
tions return to normal, check the CCN connector and cable.
Run new cable if necessary. A short in one section of the bus
can cause problems with all system elements on the bus.
Through the Navigator display, the user can access all the inputs
and outputs to check on their values and status. Because the unit is
equipped with suction pressure transducers and discharge satura-
tion temperature sensors, the Navigator display can also display
pressures typically obtained from gages. The control includes a
full alarm history, which can be accessed from the display. In addi-
tion, through the Navigator display the user can access a built-in
test routine that can be used at start-up commission and to diag-
nose operational problems with the unit. The Navigator display is
located in the control box and is standard on all units.
SUPPLY FAN
The 48/50N units are equipped with a single air-foil type supply
fan. The units have an optional high and low fan that can be select-
ed to match the airflow requirements of the application. Addition-
ally, the motor horsepower size for the supply fan is also selected
to match the airflow requirements of the application. The fan sleds
are spring isolated and driven by a single 3-phase motor. The fan
is controlled directly by the ComfortLink controls.
VARIABLE FREQUENCY DRIVE (VFD)
Supply fans are powered and controlled with VFDs. The sup-
ply fan VFD is located in the supply fan section behind an ac-
cess door. Units equipped with optional power exhaust or re-
turn fans will also be powered and controlled with a VFD. The
VFD for the power exhaust or return fan is located in the return
section behind an access door.
The N Series units use ABB VFDs. The VFDs communicate to
the ComfortLink MBB over the local equipment network (LEN).
The VFD speed is controlled directly by the ComfortLink controls
over the LEN. The interface wiring for the VFDs is shown in
Fig. 38 and the terminal designations are shown in Table 108. The
VFD has a keypad display panel that can be used for service diag-
nostics and setting the initial VFD parameters required to allow
the VFD to communicate on the LEN. Additional VFD parame-
ters are set by the ComfortLink controls, and sent to the VFD over
the LEN at power up of the VFD. The VFD faults can be reset
with the VFD keypad or through the ComfortLink controls
(Alarms  R.CUR =Yes).
Table 108 — VFD Terminal Designations
TERMINAL
U1
V1 3-phase main circuit input power supply
W1
U2
3-Phase AC Output to Motor, 0 V to
V2
Maximum Input Voltage Level
W2
X1-11 (GND)
Factory-supplied jumper
X1-12 (D-COM)
X1-10 (+24 V)
Factory-supplied jumper
X1-13 (DI-1)
X1-10 (+24 V)
Start Enable 1 (Factory-supplied jumper). When
opened the drive goes to emergency stop.
X1-16 (DI-4)
X1-28 (SCR)
X1-29 (B+)
Factory wired for local equipment network LEN
X1-30 (B-)
communication
X1-31 (AGND)
X1-32 (SCR)
POWER EXHAUST
The units can be equipped with an optional power exhaust sys-
tem. The power exhaust fan is a belt-driven, forward-curved
fan. For modulating (CV or VAV) applications, the fan is con-
trolled by the ComfortLink controls based on building pressure
sensed by the building pressure transducer. The fan speed is
modulated to maintain the building pressure set point.
RETURN FAN
The return fan power exhaust assembly consists of one belt-
drive plenum fan. The return fan is a belt-driven backward-
curved fan. The plenum fan pressurizes the plenum fan section
so that the air can either be discharged horizontally out the
back of the unit or discharged through the return air section of
the economizer.
ECONOMIZER MOTOR(S)
The economizer outside air and return air dampers are motor
actuator-driven through linkages. Communicating economizer
motors controls their position. The motor position is controlled
by the MBB through the communication bus. This allows for
accurate control of the motors as well as feedback information
and diagnostics information. The control has a self-calibration
routine that allows the motor position to be configured at initial
unit start-up. The motors are located on the economizer and
can be reached through the filter access door.
THERMISTORS AND PRESSURE TRANSDUCERS
The unit is equipped with several thermistors for measurement
of temperatures. The thermistors are summarized in Table 109.
The units have 2 pressure transducers that are connected to the
low side of the system. These 2 pressure transducers measure
the low side pressure and are used for low pressure protection
and coil freeze protection.
The units also have 2 pressure transducers that are connected to
the high side of the system. These 2 pressure transducers mea-
sure the discharge pressure and are used to cycle the condenser
fans to maintain head pressure.
By using the high and low side pressure transducers, the Com-
fortLink controls display the high and low side pressures and
saturation temperatures and a normal gage set is not required.
160
FUNCTION