Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 107

PROBLEM
Burners Will Not Ignite
Inadequate Heating
Poor Flame Characteristics
Burners Will Not Turn Off
PROBLEM
No Heat
Inadequate Heating
Heat Will Not Turn Off
Table 74 — Gas Heating Service Analysis
CAUSE
Active alarm.
No power to unit.
No power to IGC (Integrated Gas Control).
Heaters off due to time guard to prevent short
cycling.
Thermostat or occupancy schedule set point not
calling for Cooling.
No gas at main burners.
Water in gas line.
[Post Filter Option Only] Air Flow Switch.
Dirty air filters.
Gas input too low.
Thermostat or occupancy schedule set point only
calling for W1.
Unit undersized for load.
Restricted airflow.
Too much outdoor air.
Limit switch cycles main burners.
[Modulating Gas Only] No 24 vac at Modulating Gas
Module.
[Modulating Gas. Only] Modulating gas valve is not
operating.
[Post Filter Option Only] Filter Temperature Switch
Open.
Incomplete combustion (lack of combustion air)
results in: Aldehyde odors, CO, sooting flame, or
floating flame.
Unit is in Minimum on-time.
Unit running in Service Test Mode.
Table 75 — Electric Heat Service Analysis
CAUSE
Power failure.
Fuse blown or circuit breaker tripped. Check fuses
and circuit breakers in power, control and electric
heat panels.
Thermostat occupancy schedule set point not calling
for Heating.
No 24 vac at primary contactor.
No power (high voltage) to L2 of primary contactor.
Bad electrical elements.
[SCR Only] No 24 vac at SCR or Step Controller.
[SCR Only] Vernier step controller not staging up.
[Post Filter Option Only] Filter temperature switch
open.
Dirty air filters.
Restricted airflow.
Contactor failed closed.
Check active alarms using ComfortLink Navigator display.
Check power supply, fuses, wiring, and circuit breakers.
Check fuses and plugs.
Check using ComfortLink Navigator display.
Check using ComfortLink Navigator display.
Check gas line for air and purge as necessary. After purging
gas line of air, allow gas to dissipate for at least 5 minutes
before attempting to re-light unit.
Drain water and install drip.
Check switch and wiring. Switch closes when supply fan
operating.
Replace air filters.
Check gas pressure at manifold. Refer to gas valve
adjustment in Installation, Start-up, and Service Manual.
Allow time for W2 to energize.
Decrease load or increase of size of unit.
Remove restriction.
Check economizer position and configuration. Adjust
minimum position using ComfortLink Navigator display.
Check rotation of blower, thermostat heat anticipator
settings, and temperature rise of unit. Adjust as needed.
Check transformers TRAN4 and TRAN5 in gas section.
Check for 4 to 20 mA control signal. Check for 24 VAC
power at SC-30 and TR1.
Check 4 filter temperature switches located on face of post
filters. Switch opens on high temperature.
Check all screws around flue outlets and burner
compartment. Tighten as necessary.
Cracked heat exchanger, replace.
Unit is over-fired, reduce input. Adjust gas line or manifold
pressure.
Check vent for restriction. Clean as necessary.
Check orifice to burner alignment.
Check using ComfortLink Navigator display.
Check using ComfortLink Navigator display.
Check power source. Call power company.
Replace fuse or reset circuit breaker.
Check using ComfortLink Navigator display.
Check transformer and circuit breaker.
Check safety switches manual reset limit, airflow switch, and
auto limit.
Power off unit and remove high voltage wires. Check
resistance of heater, replace if open.
Check transformer and connections.
Check for 4 to 20 mA control signal. Check for 24 vac power
to step controller.
Check for filter temperature switches located on face of post
filters. switch opens on high temperature.
Replace air filters.
Remove restriction.
Inspect contactors to look for welded-closed contacts.
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REMEDY
REMEDY