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Economizer Controls
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. 46 for
typical CO
2
sensor wiring schematic.
8
7
6
5
4
32
1
2
1
HG
24 VAC
OR
24 VDC
NC
ALARM
RELAY
CONTACTS
COM
NO
}
0-10VDC
SIG COM
4-20mA
+
+
-
+
-
J3 J4
C08635
Fig. 46 -- Indoor/Outdoor Air Quality (CO
2
)Sensor
(33ZCSENCO2) -- Typical Wiring Diagram
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. 46. Connect the 4--20 mA terminal to
terminal TB3--9 and connect the SIG COM terminal to
terminal TB3--11. See Fig. 47.
J4
J5-5
J5-3
9
11
TB3
TB3
IAQ Sensor
PL
24 VAC
4-20mA
SIG COM
C11156
Fig. 47 -- Indoor CO
2
Sensor (33ZCSENCO2)
Connections
Refer to Form 33CS--67SI, PremierLink Installation,
Start--up, and Configuration Instructions, for detailed
configuration information.
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. 48. The outdoor air CO
2
sensor must be located in the
economizer outside air hood.
COVER REMOVED SIDE VIEW
C07135
Fig. 48 -- Outdoor Air Quality Sensor Cover
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. 46. Connect the 4 to 20 mA
terminal to the TB3--13 terminal of the 48HC. Connect the
SIG COM terminal to the TB3--11 terminal of the 48HC.
See Fig. 49.
48HC