Carrier 48LC Series Service And Maintenance Instructions page 32

PROBLEM CAUSE
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
Poor Flame combustion air) results in:
Characteristics. Aldehyde odors, CO, sooting
flame, or floating flame.
Burners Will Not Turn Unit is locked into Heating mode
Off. for a one minute minimum.
Table 13 – Heating Service Analysis
REMEDY
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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