Carrier 48HC 04-28 - Heating Troubleshooting; Gas Heating Service Analysis and Problem Resolution

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Heating Troubleshooting
Use the unit scrolling marquee display or a CCN device to
view the heating status display and the heating diagnostic dis-
play (see Appendix A) for information on the heating opera-
tion. Check the current alarms and alarm history for any heat-
ing alarm codes and correct any causes. (See Table 14.) Verify
any unique control configurations per installed site require-
ments or accessories. If alarms conditions are corrected and
cleared, operation of the heat stages and indoor fan may be ver-
ified by using the Service Test mode. (See Table 6.)
GAS HEAT (48HC UNITS)
See Table 19 for general gas heating service analysis. See Fig. 17
for service analysis of the IGC board logic. Check the status LED
on the IGC board for any flashing alarm codes and correct any
causes. (See Table 20.)
ELECTRIC HEAT (50HC UNITS)
See Table 21 for electric heating service analysis.
Table 19 — Gas Heating Service Analysis
PROBLEM CAUSE REMEDY
Heat Will Not Turn On. Unit is NOT configured for heat. Check heating configurations using the
ComfortLink scrolling marquee
Burners Will Not Ignite. Active alarm. Check active alarms using ComfortLink scrolling
marquee and the IGC flash codes.
No power to unit. Check power supply, fuses, wiring, and circuit
breakers.
No power to IGC (Integrated Gas Control). Check fuses and plugs.
Heaters off due to time guard to prevent short
cycling.
Check using ComfortLink scrolling marquee and
the IGC flash codes.
Thermostat or occupancy schedule set point not
calling for Cooling.
Check using ComfortLink scrolling marquee.
No gas at main burners. 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.
Water in gas line. Drain water and install drip.
Inadequate Heating. Dirty air filters. Replace air filters.
Gas input too low. Check gas pressure at manifold. Refer to gas
valve adjustment.
Thermostat or occupancy schedule set point
only calling for W1.
Allow time for W2 to energize or adjust setpoints.
Unit undersized for load. Decrease load or increase of size of unit.
Restricted airflow. Remove restriction. Check SAT compared to the
SAT heating limits.
Too much outdoor air. Check economizer position and configuration.
Adjust minimum position using ComfortLink
scrolling marquee.
Limit switch cycles main burners. Check rotation of blower, thermostat heat
anticipator settings, and temperature rise of unit.
Adjust as needed.
Poor Flame Characteristics. Incomplete combustion (lack of combustion air)
results in: Aldehyde odors, CO, sooting flame, or
floating flame.
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.
Burners Will Not Turn Off. Unit is in Minimum on-time. Check using ComfortLink scrolling marquee and
the IGC flash codes.
Unit running in Service Test mode. Check using ComfortLink scrolling marquee.
Main gas valve stuck. Turn off gas supply and unit power. Replace gas
valve.