Carrier 48PG24, Controls, Start-Up, Operation, Service And Troubleshooting Instructions, Page: 80 / 112

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Scrolling Marquee Display —
This device is the key-
pad interface used to access rooftop information, read sensor
values, and test the unit. See Fig. 26. The Scrolling Marquee
display is a 4-key, 4-character, 16-segment LED (light-emitting
diode) display. Eleven mode LEDs are located on the display
as well as an Alarm Status LED. See Scrolling Marquee
section on page 2 for further details.
Accessory Navigator™ Display —
The accessory
hand-held Navigator display can be used with the 48/50PG
series units. See Fig. 27. The Navigator display operates the
same way as the Scrolling Marquee device. The Navigator
display plugs into the LEN port on either TB2 or the ECB
board.
Carrier Comfort Network® (CCN) Interface —
The 48/50PG units can be connected to the CCN if desired.
The communication bus wiring is a shielded, 3-conductor
cable with drain wire and is field supplied and installed. The
system elements are connected to the communication bus in a
daisy chain arrangement. See Fig. 28. The positive pin of each
system element communication connector must be wired to the
positive pins of the system elements on either side of it. This is
also required for the negative and signal ground pins of each
system element. Wiring connections for CCN should be made
at TB2. See Fig. 14-17. Consult the CCN Contractor’s Manual
for further information.
NOTE: Conductors and drain wire must be 20 AWG (Ameri-
can Wire Gage) minimum stranded, tinned copper. Individual
conductors must be insulated with PVC, PVC/nylon, vinyl,
Teflon, or polyethylene. An aluminum/polyester 100% foil
shield and an outer jacket of PVC, PVC/nylon, chrome vinyl, or
Teflon with a minimum operating temperature range of –20 C
to 60 C is required. See the table below for acceptable wiring.
It is important when connecting to a CCN communication
bus that a color-coding scheme be used for the entire network
to simplify the installation. It is recommended that red be used
for the signal positive, black for the signal negative and white
for the signal ground. Use a similar scheme for cables contain-
ing different colored wires.
At each system element, the shields of its communication
bus cables must be tied together. The shield screw on TB2 can
be used to tie the cables together. If the communication bus is
entirely within one building, the resulting continuous shield
must be connected to a ground at one point only. The shield
screw on TB2 is not acceptable for grounding. If the communi-
cation bus cable exits from one building and enters another,
the shields must be connected to grounds at the lightning sup-
pressor in each building where the cable enters or exits the
building (one point per building only). 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 appropri-
ate colors for different colored cables.)
3. Connect the red wire to (+) terminal on TB2, the white
wire to COM terminal, and the black wire to the (–)
terminal.
4. The RJ14 CCN connector on TB2 can also be used, but is
only intended for temporary connection (for example, a
laptop computer running Carrier network software).
5. Restore power to unit.
Subcooler Heat Exchanger (SHX) —
The purpose
of the subcooler heat exchanger (SHX) and the subcooler TXV
is to increase the capacity of the evaporator by sending sub-
cooled liquid refrigerant into the evaporator. Normally, the
condenser subcools the liquid refrigerant by approximately
10 F. The SHX adds another 10 F to 15 F degrees of subcooling
before the refrigerant reaches the evaporator. This allows the
refrigerant to absorb more heat from the mixed air, thereby pro-
viding more cooling capacity.
The subcooler functions by taking a small percentage of the
high pressure, medium temperature liquid refrigerant which
exits the condenser and converting it into a low pressure, low
temperature gas. This is accomplished by using the subcooler
TXV. The gas is then routed through a reverse-flow heat
exchanger (SHX), which transfers heat from the remaining
liquid refrigerant in the liquid line to the reverse flow gas
refrigerant. The moderate temperature gas is then sent to the
compressor to complete the loop and the cooler liquid refriger-
ant continues its normal path to the main TXV and the
evaporator. See Fig. 29.
MANUFACTURER PART NO.
Alpha 2413 or 5463
Belden 8772
Carol C2528
West Penn 302
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 connec-
tor. If conditions return to normal, check the CCN connec-
tor and cable. Run new cable if necessary. A short in one
section of the bus can cause problems with all system ele-
ments on the bus.
Run Status
Service Test
Temperature
Pressures
Setpoints
Inputs
Outputs
Configuration
Time Clock
Operating Modes
Alarms
Alarm Status
ENTER
MODE
ESCAPE
Fig. 26 — Scrolling Marquee
Run S
tatus
Service T
est
Temperature
s
Pressures
Setpoints
Inputs
Outputs
Configura
tion
Time C
lock
Operating M
odes
Alarm
s
E NTE
R
E S C
M O D
E
Alarm Status
TIME
EWT
LWT
SETP
1 2 . 5 8
5 4 . 6
°
F 4 4 . 1
°
F 4 4 . 0
°
F
N A V
I G A
T O R
C o m f o
r t
L i n k
Fig. 27 — Accessory Navigator™ Display
a39-2239
30-650f