Carrier 48TC*D08 appendix Protective Devices, Compressor Protection

	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.

48TC

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.

2.9and 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

apilot-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	Manual
	(Circuit Breaker)

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