Carrier 48HC D17 Series Service And Maintenance Instructions page 38

Supply (Indoor) Fan Motor Protection
CAUTION
!
PERSONAL INJURY HAZARD
Failure to follow this caution can result in personal
injury.
Disconnect all electrical power when servicing the fan
motor. Apply appropriate lockout/tag- - out procedures.
Motors with 2.9 and 3.7 bhp are equipped with an
overtemperature or protection device. The type of device
depends on the motor size. See Table 6.
The High Static option supply fan motor is equipped with
a pilot- - circuit Thermik combination overtemperature/
overcurrent protection device.
automatically. Do not bypass this switch to correct
trouble. Determine the cause and correct it.
The Thermik device is a snap- - action overtemperature
protection device that is imbedded in the motor windings.
The thermik can be identified by two blue wires extending
out of the motor control box. It is a pilot- - circuit device
that is wired into the unit's 24V control circuit.
this switch reaches its trip setpoint, it opens the 24V
control circuit and causes all unit operation to cease. This
device resets automatically when the motor windings
cool. Do not bypass this switch to correct trouble.
Determine the cause and correct it.
The External Overload Breaker, is an overcurrent device
used on motors with a horsepower rating of 4.7 hp or
greater. This is a specially- - calibrated circuit breaker that
is UL recognized as a motor overload controller. When
the current to the motor exceeds the circuit breaker
setpoint, the device opens all motor power leads to the
motor shutting the motor down. Reset requires a manual
reset at the overload switch. This device (designated
IFCB) is located on the side of the supply fan housing,
behind the fan access panel. The Must Hold and Must
Trip values are listed on the side of the External Overload
Breaker.
Troubleshooting Supply Fan Motor Overload Trips
The supply fan used in 48HC units is a forward- - curved
centrifugal wheel. At a constant wheel speed, this wheel
has a characteristic that causes the fan shaft load to
DECREASE when the static 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).
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.
This device resets
Condenser Fan Motor Protection
When
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 control
transformer TRAN. Reset is manual.
The factory- - installed PremierLink Controller includes the
supply- - air temperature (SAT) sensor. The outdoor air
temperature
FIOP/accessory EconoMi$er 2 package.
Refer to Fig. 46 for PremierLink connection locations.
NOTE:
and Configuration Instructions. Have a copy of this
manual available at unit start- - up.
38
Motor overload conditions
Table 6 - - Overcurrent Device Type
Motor Size (bhp) Overload Device
1.7 Internal Linebreak
2.4 Internal Linebreak
2.9 Thermik
3.7 Thermik
External
4.7
(Circuit Breaker)
(OAT) sensor
Refer to PremierLink
Reset
Automatic
Automatic
Automatic
Automatic
Manual
is included in the
Installation, Start- - Up
t