Carrier 48TC series, Service And Maintenance Instructions, Page: 32 / 112

32
TROUBLESHOOTING SUPPLY FAN MOTOR OVER -
LOAD TRIPS
The supply fan used in 48TC units is a forward-curved centrifu
-
gal wheel. At a constant wheel speed, this wheel has a character -
istic that causes the fan shaft load to DECREASE when the stat -
ic pressure in the unit-duct system increases and to INCREASE
when the static pressure in the unit-duct system decreases (and
fan airflow rate increases). Motor overload conditions typically
develop when the unit is operated with an access panel removed,
with unfinished duct work, in an economizer-open mode, or a
leak develops in the duct system that allows a bypass back to
unit return opening.
CONDENSER FAN MOTOR PROTECTION
The condenser fan motor is internally protected against
overtemperature.
Control Circuit, 24v
The control circuit is protected against overcurrent conditions by a
circuit breaker mounted on the control transformer TRAN. Reset
is manual.
The factory-installed PremierLink Controller includes the supply-
air temperature (SAT) sensor. The outdoor air temperature (OAT)
sensor is included in the FIOP/accessory EconoMi$er 2 package.
NOTE: Refer to PremierLink Installation, Start-Up and Configu -
ration Instructions. Have a copy of this manual available at unit
start-up.
PremierLink™ Control
For details on operating units equipped with the factory-installed
PremierLink controller option, refer to the PremierLink Retrofit
Rooftop Controller Version 3.x Installation, Start-Up, and Config -
uration Instructions manual.
RTU Open Control System
For details on operating units equipped with the factory-installed
RTU Open controller, refer to the Factory-Installed RTU Open
Multi-Protocol Controller Control, Start-Up, Operation and Trou -
bleshooting manual.
GAS HEATING SYSTEM
General
The heat exchanger system consists of a gas valve feeding multi -
ple inshot burners off a manifold. The burners fire into matching
primary tubes. The tubes exit into the collector box, then into the
induced draft fan wheel inlet. The induced fan wheel discharges
into a flue passage and flue gases exit out a flue hood on the side
of the unit. The induced draft fan motor includes a Hall Effect sen -
sor circuit that confirms adequate wheel speed via the Integrated
Gas Control (IGC) board. Safety switches include a Rollout
Switch mounted at the top of the burner compartment. A limit
switch is mounted through the side of the fan deck, over the tubes.
The vestibule plate faces the tubes. See Fig. 44-46.
Fig. 44 — Burner Section Details
Fig. 45 — Inducer Assembly
Fig. 46 — Limit Switch Locations
ROLLOUT
SWITCH
GAS
VALVE
SPARK
IGNITER
FLAME
SENSOR
CAPACITOR
INDUCER
HOUSING
INDUCER
WHEEL
INDUCER
COOLING FAN
INDUCER
MOTOR
SIDE SHOT
LIMIT SWITCH
DOWN SHOT
LIMIT SWITCH