Carrier WeatherExpert 48LC Series Service And Maintenance Instructions page 30

PROBLEM
Misaligned spark electrodes.
No gas at main burners.
Water in gas line.
Burners Will Not Ignite
No power to furnace.
No 24 v power supply to control circuit.
Miswired or loose connections.
Burned-out heat anticipator in thermostat.
Broken thermostat wires.
Dirty air filter.
Gas input to unit too low.
Unit undersized for application.
Restricted airflow.
Inadequate Heating
Blower speed too low.
Limit switch cycles main burners.
Too much outdoor air.
Incomplete combustion (lack of combustion
Poor Flame
air) results in:
Characteristics Aldehyde odors, CO, sooting flame, or
floating flame.
Burners Will Not Unit is locked into Heating mode for a one
Turn Off. minute minimum.
Table 13 — Heating Service Analysis
CAUSE
Check flame ignition and sensor electrode positioning. Adjust as needed.
Check gas line for air, purge as necessary. After purging gas line of air,
allow gas to dissipate for at least 5 minutes before attempting to relight unit.
Check gas valve.
Drain water and install drip leg to trap water.
Check power supply, fuses, wiring, and circuit breaker.
Check transformer. Transformers with internal overcurrent protection
require a cool down period before resetting.
Check all wiring and wire nut connections.
Replace thermostat.
Run continuity check. Replace wires, if necessary.
Clean or replace filter as necessary.
Check gas pressure at manifold. Clock gas meter for input. If too low,
increase manifold pressure, or replace with correct orifices.
Replace with proper unit or add additional unit.
Clean filter, replace filter, or remove any restrictions.
Use high speed tap, increase fan speed, or install optional blower, as
suitable for individual units.
Check rotation of blower, thermostat heat anticipator settings, and
temperature rise of unit. Adjust as needed.
Adjust minimum position.
Check economizer operation.
Check all screws around flue outlets and burner compartment. Tighten as
necessary.
Cracked heat exchanger.
Overfired unit — reduce input, change orifices, or adjust gas line or manifold
pressure.
Check vent for restriction. Clean as necessary.
Check orifice to burner alignment.
Wait until mandatory one minute time period has elapsed or reset power to
unit.
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REMEDY