6
by the freeze condition. Unit reset is automatic when the
contacts on the freeze protection switch close again. The
contactson the freezeprotect ions witch open below 37 F.
TOWER SUMP TEMPERATURE SENSOR (50XJ
PCB3) — This sensor is used for monitoring (only) the tower
sumpte mperature.
LEAVING WATER TEMPERATURE SENSOR (50XJ
PCB3) — This sensor is used for monitoring (only) the leav-
ingwater t emperature.
BUILDING STATIC PRESSURE SENSOR (50XJ
PCB3) — This sensor is used to control both the speed of the
buildingexhaust fan and the building static pressure.
INDOOR AIR QUALITY (CO2)SENSOR(50XJ
PCB3) — This sensor monitors CO2levels.
INDOOR RELATIVE HUMIDITY SENSOR (50XJ
PCB3) —This sensor monitors and controls the humidity
controlrelay.
OUTDOOR AIR TEMPERATURE SENSOR (50XJ
PCB3) —This sensor is used to monitor outdoor air and
broadcastthe value ove r the Carrier Comfort Network (CCN).
STAGE HEATRE LAYS (50XJ PCB3) — These relays con-
trolup to four stages of el ectric heat, or other heating methods.
PUMPREQUEST R ELAY(50XJ PCB3) — This relay turns
ona tower pump when requested.
TOWER REQUEST/CONTROL RELAY(50XJ PCB3 ) —
This relay is used to activate a tower fan.
BUILDING EXHAUST FAN SPEED CONTROL (50XJ
PCB3) — This output controls building exhaust fan speed.
HUMIDITYCO NTROL RELAY(50XJ PCB3) — This relay
controls a humidifier or dehumidification device.
Wiring Control Devices— Standard c ontrols for the
50XJ require no field-wiring. Standard 50XJ controls include:
Supply Air Temperature (SAT),Duct Static Pressure (DSP),
Duct High Static Limit Switch (DHS), Filter Status Switch
(FLTS),Entering Water Temperature (EWT), Compressor Sta-
tus (CSMUX), Supply Fan Start/Stop(SF), Supply Fan Speed
(SPEED),and Mixed/A ir Return/Air sensor (MA_RA).
NOTE: The MA_RA sensor will bel ocated in thereturn air
steam if the unit does not have a water economizer,and in
the mixed airstream if the unit is equipped with a water
economizer.
For the 50BV unit, standard controls include: Duct Static
Pressure (DSP), Duct High Static Limit Switch (DHS), Com-
pressor Status (CSMUX), Supply Fan Start/Stop (SF), and
SupplyFan Speed (SPEED).
For the 50XJ unit, optional controls will be wired to the
field terminal blocks (TB5 and TB6) provided. Refer to
Fig.2A and the desc riptions below.
For the 50BV unit, optional controls are wired to field
terminalblock TB2 as shown in Fig. 2B.
EXTERNAL0 TO 10 VOLT DC RESET SIGNAL (RESET)
(50XJPCB2) — This field-supplied 0 to 10 vdc signal is used
to reset the 50XJ supply-air temperature. The controller will
scale the signal to provide 0 reset at 0 volts and 20 degrees of
reset at 10 volts. Wirethe positive of the signal to the RESET
terminaland the negative tothe C or common terminal.
SUPPLYAIR RESET (50BV) — Use a 5k ohm sensor
installed at the Entering Water Temperature sensor (EWT)
location on PCB1. For space temperature averaging, two 10k
ohmSpace Temperature Sensors (SPT)can be wired in parallel.
SPACETEMPERATURE SENSOR (50XJ PCB2) — The
spacetemperature sensor (33ZCT 55SPT)is used in the follow-
ingcas es:
• When using the optional water economizer and not using
Carrier’sComfortID™ System.
• To determine the average temperature of thespace being
served.
• To determine supply-air temperature reset, occupied
heating, unoccupied heating and cooling (refer to
Sequenceof Operation in the Start-Up section.).
Towire the sensor, perform the following (see Fig. 3).
Identifywhich cable i s for the sensor wiring.
1. Strip back the jacket from the cable for at least
3 inches. Strip 1/4-in. of insulation fromeach conduc-
tor. Cut the shield and drain wire from the sensor end
ofth e cable.
2. Wire the sensor to the SPTand C terminals on the field
terminal block (TB5). A typical 10K thermistor such
as the 33ZCT55SPT sensor may be used. If the SPT
sensor is not installed and the MA_RA (mixed air/
return air)sensor is configured for return air, the 50XJ
unit will use this sensor to control supply air reset,
occupiedheat, and unoccupied heating and cooling
SeeFig. 4 for space temperature sensor averaging.
HOT WATER OR STEAM VALVE (HWV) (50XJ
PCB2) — The HWV terminal supplies the positive signal to
controla 4 to 20 mA hot water or steam valve for occupied and
unoccupied heat. Connect the common side of the valve to the
Cterminal or anequipment ground.
Fig. 2A — Field Terminal Blocks for 50XJ Unit
Fig. 2B — Field Terminal Block for 50BV Unit