88
Table 80 — Gas Heating Service Analysis
Unit Initiates a Humidi-MiZer
Dehumidification Mode, but
Supply Air Temperature is
Overheating/Overcooling the
Space
Supply air setpoint for cooling is too high/
low
Check the unit supply air setpoint for cooling operation. This is the
temperature that Humidi-MiZer valves will modulate to meet during
a dehumidification mode.
Evaporator discharge temperature (CCT)
or supply air temperature (SAT) thermistor
is reading incorrectly.
See Thermistor Troubleshooting section on page 84.
Check if SAT thermistor is in a location that is measuring stratified
air.
Valve controlling gas bypass around the
condenser is not functioning properly
See " Modulating Valves Not Functioning Properly"
Valve controlling refrigerant flow to the con-
denser is not functioning properly
See "Modulating Valves Not Functioning Properly"
Modulating valves are not calibrated prop-
erly
See " Modulating Valves Not Functioning Properly"
Unit control software indicates a Humidi-
MiZer Reheat Mode, but the 3-way valve is
not functioning properly
See " 3-Way Valve Malfunction"
Unit is not sized to meet the load at the cur-
rent entering air and outdoor conditions.
Check product data tables or ECAT for rated capacity at current
entering air and outdoor conditions.
Low Sensible Capacity in Normal
Cooling Mode
Valve controlling gas bypass around the
condenser is stuck in an open position or
leaking
See " Modulating Valves Not Functioning Properly"
Valve controlling refrigerant flow to the
condenser is stuck in a partial open
position
See " Modulating Valves Not Functioning Properly"
General cooling mode problem See Table 78.
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.
Control calling for Cooling. Check using Comfort
Link 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 adjust-
ment in Installation, Start-up, and Service Manual.
Control calling for W1only (low heat). Allow time for W2 to energize.
Unit undersized for load. Decrease load.
Restricted airflow. Remove restriction.
Too much outdoor air. Check economizer position and configuration. Adjust mini-
mum position using ComfortLink scrolling marquee.
Limit switch cycles main burners. Check rotation of blower, thermostat heat anticipator set-
tings, 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 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 scrolling marquee.
Unit running in Service Test mode. Check using ComfortLink scrolling marquee.
Table 79 — Humidi-MiZer
®
Service Analysis (cont)
PROBLEM CAUSE REMEDY
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