19
Perform the following steps if state or local code requires
the use of conduit, or if your installation requires a cable length
of more than 8 ft:
1. Secure the probe to the fan coil unit with two field-
supplied self-drilling screws.
2. If you are extending cable length beyond 8 ft, use ple-
num rated, 20 AWG, twisted pair wire.
3. Connect the sensor leads to the fan coil controller’s
wiring harness terminal board at the terminals labeled
SAT (RED) and GND (BLK).
4. Neatly bundle and secure excess wire.
INDOOR AIR QUALITY SENSOR INSTALLATION —
The indoor air quality (IAQ) sensor accessory monitors carbon
dioxide levels. This information is used to monitor IAQ levels.
Three types of sensors are provided. The wall sensor can be
used to monitor the conditioned air space. Sensors use infrared
technology to measure the levels of CO
2
present in the air. The
wall sensor is available with or without an LCD readout to dis-
play the CO
2
level in ppm. See Fig. 23.
Sensor accessory descriptions and part numbers are shown
in Table 2. To mount the sensor, refer to the installation instruc-
tions shipped with the accessory kit.
Table 2 — CO
2
Sensor Accessories
The CO
2
sensors listed in Table 2 are all factory set for a
range of 0 to 2000 ppm and a linear voltage output of 0 to
10 vdc. Refer to the instructions supplied with the CO
2
sensor
for electrical requirements and terminal locations.
To accurately monitor the quality of the air in the condi-
tioned 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 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
air-stream.
Indoor Air Quality Sensor Wiring — To wire the sensors
after they are mounted in the conditioned air space or outdoor
location, see Fig. 24 and the instructions shipped with the sen-
sors. For each sensor, use two 2-conductor 18 AWG twisted-
pair cables (unshielded) to connect the separate isolated 24 vac
power source to the sensor and to connect the sensor to the con-
trol board terminals. To connect the sensor to the control board,
identify the positive (0-10 VDC) and ground (SIG COM) ter-
minals on the sensor. Connect the 1-10 VDC terminal to termi-
nal IAQ and connect the SIG COM terminal to terminal GND.
HUMIDITY SENSOR (WALL-MOUNTED) INSTALLA-
TION — The accessory space humidity sensor is installed on
an interior wall to measure the relative humidity of the air with-
in the occupied space. See Fig. 25.
The use of a standard 2- x 4-in. electrical box to accommo-
date the wiring is recommended for installation. The sensor can
be mounted directly on the wall, if acceptable by local codes.
If the sensor is installed directly on a wall surface, install the
humidity sensor using 2 screws and 2 hollow wall anchors
(field-supplied);
do not overtighten screws.
See Fig. 15.
The sensor must be mounted vertically on the wall. The
Carrier logo should be oriented correctly when the sensor is
properly mounted.
DO NOT mount the sensor in drafty areas such as near heat-
ing or air-conditioning ducts, open windows, fans, or over heat
sources such as baseboard heaters, radiators, or wall-mounted
light dimmers. Sensors mounted in those areas will produce in-
accurate readings.
Avoid corner locations. Allow at least 4 ft between the sen-
sor and any corner. Airflow near corners tends to be reduced,
resulting in erratic sensor readings.
Sensor should be vertically mounted approximately 5 ft up
from the floor, beside the space temperature sensor.
For distances up to 500 feet, use a 3-conductor, 18 or
20 AWG cable. A CCN communication cable can be used,
although the shield is not required. The shield must be removed
from the sensor end of the cable if this cable is used. See
Fig. 26 for wiring details.
The power for the sensor is provided by the control board.
The board provides 24 vdc for the sensor. No additional power
source is required.
To wire the sensor, perform the following:
1. At the sensor, remove 4-in. of jacket from the cable.
Strip
1
/
4
-in. of insulation from each conductor. Route
the cable through the wire clearance opening in the
center of the sensor.
2. Connect the RED wire to the sensor screw terminal
marked (+).
3. Install one lead from the resistor (supplied with the
sensor) and the WHITE wire, into the sensor screw ter-
minal marked (–). After tightening the screw terminal,
test the connection by pulling gently on the resistor
lead.
4. Connect the remaining lead from the resistor to the
BLACK wire and secure using a field-supplied closed
end type crimp connector or wire nut.
CO
2
SENSOR
ACCESSORY
PART NUMBERS
DESCRIPTION
33ZCSENCO2
Wall Mount Sensor (with display)
33ZCT55CO2
Wall Mount Sensor with
33ZCT55SPT space temperature
sensor (no display)
33ZCT56CO2
Wall Mount Sensor with
33ZCT56SPT space temperature
sensor and set point adjustment (no
display)
Do NOT clean or touch the sensing element with chemical
solvents; they can permanently damage the sensor.
3.25
(8.3)
5.625
(14.3)
1.125
(2.9)
0.25
(0.8)
5
(12.7)
NOTE: Dimensions are in inches.
Dimensions in ( ) are in centimeters.
Fig. 23 — Indoor Air Quality (CO
2
) Sensor
(33ZCSENCO2)
→
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