![background image](http://html1.mh-extra.com/html/carrier/48lc-14/48lc-14_service-and-maintenance-instructions_2561045021.webp)
21
Troubleshooting
CONTROLLER’S TROUBLE LED IS ON
1. Check the Trouble LED on each sensor connected to the con
-
troller. If a sensor’s Trouble LED is on, determine the cause
and make the necessary repairs.
2. Check the wiring between the sensor and the controller. If
wiring is loose or missing, repair or replace as required.
CONTROLLER’S TROUBLE LED IS FLASHING
1. One or both of the sensors is 100% dirty.
2. Determine which Dirty LED is flashing then clean that sensor
assembly as described in the detector cleaning section.
SENSOR’S TROUBLE LED IS ON
1. Check the sensor’s Dirty LED. If it is flashing, the sensor is
dirty and must be cleaned.
2. Check the sensor’s cover. If it is loose or missing, secure the
cover to the sensor housing.
3. Replace sensor assembly.
SENSOR’S POWER LED IS OFF
1. Check the controller’s Power LED. If it is off, determine why
the controller does not have power and make the necessary
repairs.
2. Check the wiring between the sensor and the controller. If
wiring is loose or missing, repair or replace as required.
CONTROLLER’S POWER LED IS OFF
1. Make sure the circuit supplying power to the controller 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 repair 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. 24. Repair or replace loose or missing wiring.
2. Configure the sensor dirty test to activate the controller’s
supervision relay. See “Changing sensor dirty test operation.”
SENSOR’S TROUBLE LED IS ON, BUT THE CONTROL
-
LER’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 ex
-
cessively 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 evapora
-
tor 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 protec
-
tion 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 cor
-
rect trouble. Determine the cause and correct it.
The external motor overload device is a specially-calibrated cir
-
cuit 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 48LC 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 in
-
creases). 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 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.