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To wire the return air enthalpy sensor, perform the
following:
1. Use a 2--conductor, 18 or 20 AWG, twisted pair cable
to connect the return air enthalpy sensor to the enthal-
py controller.
2. Connect the field--supplied RED wire to (+) spade
connector on the return air enthalpy sensor and the
(+) terminal on the enthalpy controller. Connect the
BLK wire to (--) spade connector on the return air en-
thalpy sensor and the (--) terminal on the enthalpy
controller.
Indoor Air Quality (CO
2
sensor) —
The indoor air quality sensor accessory monitors space
carbon dioxide (CO
2
) levels. This information is used to
monitor IAQ levels. Several types of sensors are available,
for wall mounting in the space or in return duct, with and
without LCD display, and in combination with space
temperature sensors. Sensors use infrared technology to
measure the levels of CO
2
present in the space air.
The CO
2
sensors are all factory set for a range of 0 to
2000 ppm and a linear mA output of 4 to 20. Refer to the
instructions supplied with the CO
2
sensor for electrical
requirements and terminal locations. See Fig. 38 for
typical CO
2
sensor wiring schematic.
To accurately monitor the quality of the air in the
conditioned air space, locate the sensor near a return--air
grille (if present) so it senses the concentration of CO
2
leaving the space. The sensor should be mounted in a
location to avoid direct breath contact.
Do not mount the IAQ sensor in drafty areas such as near
supply ducts, open windows, fans, or over heat sources.
Allow at least 3 ft (0.9 m) between the sensor and any
corner. Avoid mounting the sensor where it is influenced
by the supply air; the sensor gives inaccurate readings if
the supply air is blown directly onto the sensor or if the
supply air does not have a chance to mix with the room air
before it is drawn into the return airstream.
Wiring the Indoor Air Quality Sensor: For each sensor,
use two 2--conductor 18 AWG (American Wire Gage)
twisted--pair cables (unshielded) to connect the separate
isolated 24 vac power source to the sensor and to connect
the sensor to the control board terminals.
To connect the sensor to the control, identify the positive
(4 to 20 mA) and ground (SIG COM) terminals on the
sensor. See Fig. 38. Connect the 4--20 mA terminal to
RTU--MP J4--2 and connect the SIG COM terminal to
RTU--MP J4--3. See Fig. 53.
SEN
COM
J4-2
J4-3
IAQ Sensor
24 VAC
C08462
Fig. 53 -- RTU--MP / Indoor CO
2
Sensor
(33ZCSENCO2) Connections
Outdoor Air Quality Sensor
(PNO 33ZCSENCO2 plus weatherproof enclosure) —
The outdoor air CO
2
sensor is designed to monitor carbon
dioxide (CO
2
) levels in the outside ventilation air and
interface with the ventilation damper in an HVAC system.
The OAQ sensor is packaged with an outdoor cover. See
Fig. 40. The outdoor air CO
2
sensor must be located in the
economizer outside air hood.
Wiring the Outdoor Air CO
2
Sensor — A dedicated power
supply is required for this sensor. A two--wire cable is
required to wire the dedicated power supply for the sensor.
The two wires should be connected to the power supply
and terminals 1 and 2.
To connect the sensor to the control, identify the positive
(4 to 20 mA) and ground (SIG COM) terminals on the
OAQ sensor. See Fig. 38. Connect the 4 to 20 mA
terminal to RTU--MP J4--5. Connect the SIG COM
terminal to RTU--MP J4--6.
SEN
COM
J4-5
J4-6
OAQ Sensor/RH Sensor
24 VAC
C08463
Fig. 54 -- RTU--MP / Outdoor CO
2
Sensor
(33ZCSENCO2) Connections
On 50HCQ units equipped with factory--installed Smoke
Detector(s), the smoke detector controller implements the
unit shutdown through its NC contact set connected to the
unit’s CTB input. The FSD function is initiated via the
smoke detector’s Alarm NO contact set. The RTU--MP
controller communicates the smoke detector’s tripped
status to the BAS building control. See Fig. 49, the
RTU--MP system control wiring schematic.
The Fire Shutdown Switch configuration,
MENU
→
Config
→
Inputs
→
input 5, identifies the
normally open status of this input when there is no fire
alarm.
Connecting Discrete Inputs —
Filter Status: The filter status accessory is a
field--installed accessory. This accessory detects plugged
filters. When installing this accessory, the unit must be
configured for filter status by setting
MENU
→
Config
→
Inputs
→
input3,5,8,or9to Filter
Status and normally open (N/O) or normally closed (N/C).
Input 8 or 9 is recommended for easy of installation. Refer
to Fig. 47 and Fig. 49 for wire terminations at J5.
Fan Status: The fan status accessory is a field--installed
accessory. This accessory detects when the indoor fan is
blowing air. When installing this accessory, the unit must
be configured for fan status by setting
MENU
→
Config
→
Inputs
→
input3,5,8,or9to Fan
Status and normally open (N/O) or normally closed (N/C).
50HCQA