Filter
Top Products
6
by the freeze condition. Unit reset is automatic when the
contacts on the freeze protection switch close again. The
contacts on the freeze protection switch open below 37 F.
TOWER SUMP TEMPERATURE SENSOR (50XJ
PCB3) — This sensor is used for monitoring (only) the tower
sump temperature.
LEAVING WATER TEMPERATURE SENSOR (50XJ
PCB3) — This sensor is used for monitoring (only) the leav-
ing water temperature.
BUILDING STATIC PRESSURE SENSOR (50XJ
PCB3) — This sensor is used to control both the speed of the
building exhaust fan and the building static pressure.
INDOOR AIR QUALITY (CO
2
)SENSOR(50XJ
PCB3) — This sensor monitors CO
2
levels.
INDOOR RELATIVE HUMIDITY SENSOR (50XJ
PCB3) — This sensor monitors and controls the humidity
control relay.
OUTDOOR AIR TEMPERATURE SENSOR (50XJ
PCB3) — This sensor is used to monitor outdoor air and
broadcast the value over the Carrier Comfort Network (CCN).
STAGE HEAT RELAYS (50XJ PCB3) — These relays con-
trol up to four stages of electric heat, or other heating methods.
PUMP REQUEST RELAY (50XJ PCB3) — This relay turns
on a 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.
HUMIDITY CONTROL RELAY (50XJ PCB3) — This relay
controls a humidifier or dehumidification device.
Wiring Control Devices — Standard controls 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/Air Return/Air sensor (MA_RA).
NOTE: The MA_RA sensor will be located in the return 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
Supply Fan 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 descriptions below.
For the 50BV unit, optional controls are wired to field
terminal block TB2 as shown in Fig. 2B.
EXTERNAL 0 TO 10 VOLT DC RESET SIGNAL (RESET)
(50XJ PCB2) — 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. Wire the positive of the signal to the RESET
terminal and the negative to the C or common terminal.
SUPPLY AIR RESET (50BV) — Use a 5k ohm sensor
installed at the Entering Water Temperature sensor (EWT)
location on PCB1. For space temperature averaging, two 10k
ohm Space Temperature Sensors (SPT) can be wired in parallel.
SPACE TEMPERATURE SENSOR (50XJ PCB2) — The
space temperature sensor (33ZCT55SPT) is used in the follow-
ing cases:
• When using the optional water economizer and not using
Carrier’s ComfortID™ System.
• To determine the average temperature of the space being
served.
• To determine supply-air temperature reset, occupied
heating, unoccupied heating and cooling (refer to
Sequence of Operation in the Start-Up section.).
To wire the sensor, perform the following (see Fig. 3).
Identify which cable is for the sensor wiring.
1. Strip back the jacket from the cable for at least
3 inches. Strip
1
/
4
-in. of insulation from each conduc-
tor. Cut the shield and drain wire from the sensor end
of the cable.
2. Wire the sensor to the SPT and 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,
occupied heat, and unoccupied heating and cooling
See Fig. 4 for space temperature sensor averaging.
HOT WATER OR STEAM VALVE (HWV) (50XJ
PCB2) — The HWV terminal supplies the positive signal to
control a 4 to 20 mA hot water or steam valve for occupied and
unoccupied heat. Connect the common side of the valve to the
C terminal or an equipment ground.
Fig. 2A — Field Terminal Blocks for 50XJ Unit
Fig. 2B — Field Terminal Block for 50BV Unit