105
Table 86 — Gas Heating Service Analysis
Table 87 — Electric Heat Service Analysis
Modulating Valves Not Functioning
Properly
Faulty wire connections Check that the valve wiring is properly connected from the valve, entering the
control box and at the EXV board.
EXV board malfunction Check alarm history for A169 (Expansion Valve Control Board Comm Failure).
Valve is stuck open/closed Use Service Test to manually manipulate the valve position and confirm supply
air temperature changes during operation.
Run valve calibration through Service Test.
Check valve motor for open or short circuited windings. Shut down power to the
unit and connect ohmmeter probes across the black and white terminals.
Resistance should measure 75 Ohms ±10%. Next, connect ohmmeter probes
across the red and green terminals. Resistance should measure 75 Ohms
±10%. The meter should not show an “open” or a “short” when a winding leg is
measured. If either occurs, replace the valve.
Valve is not calibrated properly Run valve calibration through Service Test.
PROBLEM CAUSE REMEDY
Burners Will Not Ignite. Active alarm. Check active alarms using ComfortLink scrolling
marquee.
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.
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 system adjustment in this man-
ual.
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 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 nec-
essary.
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.
Unit running in Service Test Mode. Check using ComfortLink scrolling marquee.
PROBLEM CAUSE REMEDY
No Heat. Power failure. Call power company.
Fuse blown or circuit breaker tripped. Check
CB1, CB2, and CB3.
Replace fuse or reset circuit breaker.
Thermostat occupancy schedule set point not
calling for Heating.
Check using ComfortLink scrolling marquee.
No 24 vac at primary contactor. Check transformer and circuit breaker.
No power (high voltage) to L2 of primary con-
tactor.
Check safety switches “one-shot” backup and auto limit.
Bad electrical elements. Power off unit and remove high voltage wires. Check resistance of heater,
replace if open.
Table 85 — Humidi-MiZer
®
Service Analysis (cont)
PROBLEM CAUSE REMEDY
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