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Table 74 — Gas Heating Service Analysis
Table 75 — Electric Heat Service Analysis
PROBLEM CAUSE REMEDY
Burners Will Not Ignite. Active alarm. Check active alarms using ComfortLink Navigator display.
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 Navigator display.
Thermostat or occupancy schedule set point not
calling for Cooling.
Check using ComfortLink Navigator display.
No gas at main burners. Check gas line for air and purge as necessary. After purg-
ing gas line of air, allow gas to dissipate for at least 5 min-
utes before attempting to re-light unit.
Water in gas line. Drain water and install drip.
[Post Filter Option Only] - Air Flow Switch Check switch and wiring. Switch closes when supply fan
operating.
Inadequate Heating. Dirty air filters. Replace air filters.
Gas input too low. Check gas pressure at manifold. Refer to gas valve adjust-
ment in Installation, Start-up, and Service Manual.
Thermostat or occupancy schedule set point only
calling for W1.
Allow time for W2 to energize.
Unit undersized for load. Decrease load or increase of size of unit.
Restricted airflow. Remove restriction.
Too much outdoor air. Check economizer position and configuration. Adjust mini-
mum position using ComfortLink Navigator display.
Limit switch cycles main burners. Check rotation of blower, thermostat heat anticipator set-
tings, and temperature rise of unit. Adjust as needed.
[Modulating Gas Only] No 24 vac at Modulating
Gas Module
Check transformers TRAN4 and TRAN5 in gas section.
[Modulating Gas. Only] Modulating gas valve is
not operating.
Check for 4 - 20 mA control signal. Check for 24 VAC
power at SC-30 and TR1.
[Post Filter Option Only] Filter Temperature Switch
Open.
Check 4 filter temperature switches located on face of post
filters. Switch opens on high temperature.
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 compart-
ment. 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 Navigator display.
Unit running in Service Test Mode. Check using ComfortLink Navigator display.
PROBLEM CAUSE REMEDY
No Heat. Power failure. Check power source. Call power company.
Fuse blown or circuit breaker tripped. Check fuses
and circuit breakers in power, control and electric
heat panels.
Replace fuse or reset circuit breaker.
Thermostat occupancy schedule set point not call-
ing for Heating.
Check using ComfortLink Navigator display.
No 24 vac at primary contactor. Check transformer and circuit breaker.
No power (high voltage) to L2 of primary contactor. Check safety switches manual reset limit, airflow switch,
and auto limit.
Bad electrical elements. Power off unit and remove high voltage wires. Check resis-
tance of heater, replace if open.
[SCR Only] No 24 vac at SCR or Step Controller Check transformer and connections.
[SCR Only] Vernier step controller not staging up. Check for 4 - 20 mA control signal. Check for 24 vac power
to step controller.
[Post Filter Option Only] Filter temperature switch
open
Check for filter temperature switches located on face of
post filters. switch opens on high temperature.
Inadequate Heating. Dirty air filters. Replace air filters.
Air flow restriction. Remove restriction.
Heat Will Not Turn Off. Contactor failed closed. Instpect contactors to look for welded - closed contacts.
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