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4
At each system element, the shields of its communication
bus cables must be tied together. If the communication bus is
entirely within one building, the resulting continuous shield
must be connected to a ground at one point only. If the commu-
nication bus cable exits from one building and enters another,
the shields must be connected to grounds at the lightning
suppressor 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 SCN 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 TB3 of the plug,
the white wire to COM terminal, and the black wire to the
(–) terminal.
4. The RJ14 SCN connector on TB3 can also be used, but is
only intended for temporary connection (for example, a
laptop computer running Service Tool).
Table 2 — Thermistor Designations
LEGEND
Table 3 — Status Switches
Table 4 — Output Relays
Table 5 — SCN Communication Bus Wiring
OPERATING DATA
Sensors —
The electronic control uses 3 to 6 thermistors to
sense temperatures for controlling chiller operation. See
Table 2. These sensors are outlined below. Thermistors T1, T2,
T9 and accessory suction gas temperatures (T7,T8) are 5 kΩ at
77 F (25 C) and are identical in temperature versus resistance
and voltage drop performance. Thermistor T10 is 10 kΩ at
77 F (25 C) and has a different temperature vs. resistance and
voltage drop performance. See Thermistors section for
temperature-resistance-voltage drop characteristics.
T1 — COOLER LEAVING FLUID SENSOR — On 30RA010-
030 sizes, this thermistor is installed in a friction fit well at the
bottom of the brazed-plate heat exchanger on the control box
side. For 30RA032-055 sizes, this thermistor is installed in a
well in the factory-installed leaving fluid piping coming from
the bottom of the brazed-plate heat exchanger opposite the
control box side.
T2 — COOLER ENTERING FLUID SENSOR — On 30RA010-
030 sizes, this thermistor is installed in a friction fit well at the
top of the brazed-plate heat exchanger on the control box side.
For 30RA032-055 sizes, this thermistor is installed in a well in
the factory-installed entering fluid piping coming from the top
of the brazed-plate heat exchanger opposite the control box
side.
T7,T8 — COMPRESSOR RETURN GAS TEMPERA-
TURE SENSOR (ACCESSORY) — A well for this sensor
is factory installed in each circuit's suction line. If desired, a
5 kΩ thermistor (Sterling part number HH79NZ029) can be
installed in this well and connected to the Main Base Board
as shown in Table 2. Use the Scrolling Marquee display to con-
figure the sensor (Configuration mode, sub-mode OPT1 —
enable item RG.EN).
T9 — OUTDOOR-AIR TEMPERATURE SENSOR —
This sensor is factory-installed on a bracket at the left side of
compressor A1 on 30RA010-030 models. For models
30RA032-055, it is installed behind the panel below the
control box center door.
IMPORTANT: A shorted SCN bus cable will prevent some
routines from running and may prevent the unit from start-
ing. If abnormal conditions occur, unplug the connector. If
conditions return to normal, check the SCN 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.
THERMISTOR
NO.
PIN
CONNECTION
POINT
THERMISTOR INPUT
T1 J8-13,14 (MBB) Cooler Leaving Fluid
T2 J8-11,12 (MBB) Cooler Entering Fluid
T7
J8-1,2 (MBB) Circuit A Return Gas
Temperature (Accessory)
T8
J8-3,4 (MBB) Circuit B (032-055 only) Return
Gas Temperature (Accessory)
T9
J8-7,8 (MBB) Outdoor-Air Temperature
Sensor
T10
J8-5,6 (MBB)
TB5-5,6
Accessory Remote Space
Temperature Sensor or
Dual LWT Sensor
LWT — Leaving Water Temperature
MBB — Main Base Board
STATUS
SWITCH
PIN CONNECTION
POINT
Chilled Water Pump 1 J7-1,2
Chilled Water Pump 2 J7-3,4
Remote On/Off TB5-9,10
Cooler Flow Switch J7-9,10
Compressor Fault Signal, A1 J9-11,12
Compressor Fault Signal, A2 J9-5,6
Compressor Fault Signal, B1 J9-8,9
Compressor Fault Signal, B2 J9-2,3
RELAY
NO.
DESCRIPTION
K1
Energize Compressor A1 (010-030)
Energize Compressor A1 and Condenser Fan A1 (032-055)
K2
Energize Compressor B1 and Condenser Fan B1 at Low
Speed (032-040)
Energize Compressor B1 and Condenser Fan B1 (042-055)
K3 Energize Chilled Water Pump 1 Output
K4 Energize Chilled Water Pump 2 Output
K5 Energize Compressor A2 (all but 010, 015 60Hz)
K6 Energize Compressor B2 (042-055 only)
K7 Alarm Relay
K8 Cooler/Pump Heater
K9
Energize Condenser Fan at Low Speed (010-018)
Energize Condenser Fan A1 (022-030)
Energize Condenser Fan A2 (032-055)
K10
Energize Condenser Fan at High Speed (010-018)
Energize Condenser Fan A2 (022-030)
Energize Condenser Fan B1 at High Speed (032-040)
Energize Condenser Fan B2 (042-055)
K11 Minimum Load Valve
MANUFACTURER
PART NO.
Regular Wiring Plenum Wiring
Alpha 1895 —
American A21451 A48301
Belden 8205 884421
Columbia D6451 —
Manhattan M13402 M64430
Quabik 6130 —