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Protective devices – Carrier 48TC*D08 User Manual

Page 24

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24

Table 3 – Detector Indicators

CONTROL OR INDICATOR

DESCRIPTION

Magnetic test/reset switch

Resets the sensor when it is in the alarm or trouble state. Activates or tests the sensor when it is in

the normal state.

Alarm LED

Indicates the sensor is in the alarm state.

Trouble LED

Indicates the sensor is in the trouble state.

Dirty LED

Indicates the amount of environmental compensation used by the sensor

(flashing continuously = 100%)

Power LED

Indicates the sensor is energized.

Controller’s Power LED is Off

1. Make sure the circuit supplying power to the control-

ler is operational. If not, make sure JP2 and JP3 are

set correctly on the controller before applying power.

2. Verify that power is applied to the controller’s supply

input terminals. If power is not present, replace or re-

pair wiring as required.

Remote Test/Reset Station’s Trouble LED Does Not

flash When Performing a Dirty Test, But the

Controller’s Trouble LED Does

1. Verify that the remote test/station is wired as shown

in Fig. 26. Repair or replace loose or missing wiring.

2. Configure the sensor dirty test to activate the control-

ler’s supervision relay. See “Changing sensor dirty

test operation.”

Sensor’s Trouble LED is On, But the Controller’s

Trouble LED is OFF
Remove JP1 on the controller.

PROTECTIVE DEVICES

Compressor Protection

Overcurrent
Each compressor has internal linebreak motor protection.

Reset is automatic after compressor motor has cooled.
Overtemperature
Each compressor has an internal protector to protect it

against excessively high discharge gas temperatures. Reset

is automatic.
High Pressure Switch
Each system is provided with a high pressure switch

mounted on the discharge line. The switch is

stem--mounted and brazed into the discharge tube. Trip

setting is 630 psig +/-- 10 psig (4344 +/-- 69 kPa) when

hot. Reset is automatic at 505 psig (3482 kPa).
Low Pressure Switch
Each 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
Disconnect and lockout power when servicing fan motor.

2.9 and 3.7 bhp motors are equipped with an

overtemperature or protection device. The type of device

depends on the motor size. See Table 4.

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 imbedded in the motor windings.

It is a pilot--circuit device that is wired into the unit’s 24--v

control circuit. When this switch reaches its trip setpoint,

it opens the 24--v 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

motor

overload

device

is

a

specially--calibrated circuit breaker that is UL recognized

as a motor overload controller.

It is an overcurrent

device.

When the motor current exceeds the circuit

breaker setpoint, the device opens all motor power leads

and the motor shuts 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.

Troubleshooting supply fan motor overload trips: The

supply fan used in 48TC 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 4 -- 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

48TC