Carrier 48HC D17 Series Service And Maintenance Instructions page 31

housing with a single captive screw for easy access to the
wiring terminals. The controller has three LEDs: Power,
Trouble and Alarm. A manual test/reset button is located
on the cover face.
DUCT SMOKE SENSOR
CONTROLLER
CONTROLLER HOUSING
AND ELECTRONICS
CONDUIT COUPLINGS
(SUPPLIED BY INSTALLER)
FASTENER (2X)
ALARM
Fig. 37 - - Controller Assembly
Sensor
The sensor includes a plastic housing, a printed circuit
board, a clear plastic cover, a sampling tube inlet and an
exhaust tube. See Fig. 38. The sampling tube, when used,
and exhaust tube are attached during installation. The
sampling tube varies in length depending on the size of
the rooftop unit. The clear plastic cover permits visual
inspections without having to disassemble the sensor. The
cover attaches to the sensor housing using four captive
screws and forms an airtight chamber around the sensing
electronics. Each sensor includes a harness with an RJ45
terminal for connecting to the controller. Each sensor has
four LEDs: Power, Trouble, Alarm and Dirty. A manual
test/reset button is located on the left- - side of the housing.
Air is introduced to the duct smoke detector sensor's
sensing chamber through a sampling tube that extends into
the HVAC duct and is directed back into the ventilation
system through a shorter exhaust tube. The difference in
air pressure between the two tubes pulls the sampled air
through the sensing chamber. When a sufficient amount of
smoke is detected in the sensing chamber, the sensor
signals an alarm state and the controller automatically
takes the appropriate action to shut down fans and
blowers, change over air handling systems, notify the fire
alarm control panel, etc.
The sensor uses a photoelectric (light scattering principle)
process called differential sensing preventing gradual
environmental changes from triggering false alarms. A
rapid change in environmental conditions, such as smoke
CONDUIT NUTS
(SUPPLIED BY INSTALLER)
CONDUIT SUPPORT PLATE
TERMINAL BLOCK COVER
COVER GASKET
(ORDERING OPTION)
CONTROLLER
COVER
TROUBLE
POWER
TEST/RESET
SWITCH
C08208
from a fire, causes the sensor to signal an alarm state, but
dust and debris accumulated over time does not.
EXHAUST TUBE
EXHAUST GASKET
A
SEE DETAIL
INTAKE
GASKET
TSD-CO2
(ORDERING OPTION)
PLUG
SAMPLING TUBE
(ORDERED SEPARATELY)
COUPLING
DETAIL A
MAGNETIC
TEST/RESET
SWITCH
TROUBLE
Fig. 38 - - Smoke Detector Sensor
For installations using two sensors, the duct smoke
detector does not differentiate which sensor signals an
alarm or trouble condition.
Smoke Detector Locations
Supply Air
The Supply Air smoke detector sensor is located to the
left of the unit's indoor supply fan. See Fig. 39. Access is
through the fan access panel. There is no sampling tube
used at this location. The sampling tube inlet extends
through the side plate of the fan housing into a high
pressure area. The control module is mounted in the left
side of the control box, accessed by opening the Control
Box access door.
SUPPLY AIR
SMOKE
DETECTOR
SENSOR
Fig. 39 - - Typical Supply Air Smoke Detector Sensor
Location
31
DUCT SMOKE SENSOR
SENSOR HOUSING
AND ELECTRONICS
COVER GASKET
(ORDERING OPTION)
SENSOR
COVER
ALARM POWER
DIRTY
C08209
C10325