36
Low Pressure Switch
The system is protected against a loss of charge and low
evaporator coil loading condition by a low pressure switch
located on the suction line near the compressor. The
switch is stem−mounted. Trip setting is 54 psig ± 5 psig
(372 ± 34 kPa). Reset is automatic at 117 ± 5 psig (807 ±
34 kPa).
Supply (Indoor) Fan Motor Protection
PERSONAL INJURY HAZARD
Failure to follow this WARNING can result in
personal injury.
Disconnect all electrical power when servicing the fan
motor. Apply appropriate lockout/tagout procedures.
!
WARNING
Motors with 2.9 and 3.7 bhp are equipped with an internal
overtemperature or protection device. The type of device
depends on the motor size. See Table 8.
The High Static option supply fan motor is equipped with
a pilot−circuit Thermix combination overtemperature/
overcurrent protection device. This device resets
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 embedded 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.
When 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 50TC 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). 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.
Table 8 – Overcurrent Device Type
Motor Size (bhp) Overload Device Reset
1.7 Internal Linebreak Automatic
2.4 Internal Linebreak Automatic
2.9 Thermik Automatic
3.7 Thermik Automatic
4.7 External (circuit breaker) Manual
Condenser Fan Motor Protection
The condenser fan motor is internally protected against
overtemperature.
Control Circuit, 24−V
The control circuit is protected against overcurrent
conditions by a circuit breaker mounted on the control
transformer TRAN. Reset is manual.
PREMIERLINK] CONTROL
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.
Refer to Fig. 43 for PremierLink connection locations.
NOTE: Refer to PremierLink Installation, Start−Up
and Configuration Instructions. Have a copy of this
manual available at unit start−up.
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