Carrier 50FC A04 Series, Service And Maintenance Instructions, Page: 22 / 112

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SMOKE DETECTORS
Smoke detectors are available as factory-installed options on
50FC models. Smoke detectors may be specified for supply air
only, for return air without or with economizer, or in combina-
tion of supply air and return air. Return air smoke detectors are
arranged for vertical return configurations only. All compo-
nents necessary for operation are factory-provided and mount-
ed. The unit is factory-configured for immediate smoke detec-
tor shutdown operation; additional wiring or modifications to
unit terminal board may be necessary to complete the unit and
smoke detector configuration to meet project requirements.
System
The smoke detector system consists of a four-wire controller and
one or two sensors. Its primary function is to shut down the roof-
top unit in order to prevent smoke from circulating throughout
the building. It is not to be used as a life saving device.
Controller
The controller (see Fig. 40) includes a controller housing, a
printed circuit board, and a clear plastic cover. The controller
can be connected to one or two compatible duct smoke sensors.
The clear plastic cover is secured to the housing with a single
captive screw for easy access to the wiring terminals. The con-
troller has three LEDs (for Power, Trouble and Alarm) and a
manual test/reset button (on the cover face).
Fig. 40 — Controller Assembly
Smoke Detector Sensor
The smoke detector sensor (see Fig. 41) includes a plastic
housing, a printed circuit board, a clear plastic cover, a sam-
pling tube inlet and an exhaust tube. 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 air-
tight chamber around the sensing electronics. Each sensor in-
cludes a harness with an RJ45 terminal for connecting to the
controller. Each sensor has four LEDs (for Power, Trouble,
Alarm and Dirty) and a manual test/reset button (on the left-
side of the housing).
Fig. 41 — Smoke Detector Sensor
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 process called differential sensing to prevent
gradual environmental changes from triggering false alarms. A
rapid change in environmental conditions, such as smoke from
a fire, causes the sensor to signal an alarm state but dust and
debris accumulated over time does not.
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.
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 right of
the unit’s indoor (supply) fan. See Fig. 42. Access is through
the fan access panel. The sampling tube inlet extends through
the fan deck (into a high pressure area). The controller is locat-
ed on a bracket to the right of the return filter, accessed through
the lift-off filter panel.
DUCT S MOKE S EN S OR
CONTROLLER
CONDUIT NUT S
( S UPPLIED BY IN S TALLER)
CONDUIT S UPPORT PLATE
TERMINAL BLOCK COVER
COVER GA S KET
(ORDERING OPTION)
CONTROLLER
COVER
FA S TENER (2X)
CONDUIT COUPLING S
( S UPPLIED BY IN S TALLER)
CONTROLLER HOU S ING
AND ELECTRONIC S
ALARM
TROUBLE
POWER
TE S T/RE S ET
S WITCH
SEE DETAIL
A
DETAIL
A
PLUG
SAMPLING TUBE
(ORDERED SEPARATELY)
COUPLING
MAGNETIC
TEST/RESET
SWITCH
ALARM
TROUBLE
POWER
DIRTY
SENSOR
COVER
COVER GASKET
(ORDERING OPTION)
SENSOR HOUSING
AND ELECTRONICS
EXHAUST GASKET
EXHAUST TUBE
DUCT SMOKE SENSOR
INTAKE
GASKET
TSD-CO2
(ORDERING OPTION)