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Minimum Heating Entering Air Temperature
When operating on first stage heating, the minimum
temperature of air entering the dimpled heat exchanger is
50_F continuous and 45_F intermittent for standard heat
exchangers and 40_F continuous and 35_F intermittent for
stainless steel heat exchangers. To operate at lower
mixed--air temperatures, a field--supplied outdoor--air
thermostat must be used to initiate both stages of heat
when the temperature is below the minimum required
temperature to e nsure full fire operation. Wire the
outdoor--air thermostat OALT (part no. HH22AG106) in
series with the second stage gas valve. See Fig. 40. Set the
outdoor--air thermosta t at 35_F for stainless steel heat
excha ngers or 45_F for standard heat exchangers. This
temperature setting will bring on the second stage of heat
whenever the ambient temperature is below the thermostat
setpoint. Indoor comfort may be compromised when
heating is initiated using low entering air temperatures
with insufficient heating temperature rise.
LCTB
W2
Thermostat
TH1
TH2
W1
W1
W2
OALT
C08442
Fig. 40 -- OATL Connections
Troubleshooting Heating System
Refer to Table 13 and 14 for additional troubleshooting
topics.
Table 13 – Heating Service Analysis
PROBLEM CAUSE REMEDY
Burners Will Not Ignite.
Misaligned spark electrodes.
Check flame ignition and s ensor electrode positioning.
Adjust as needed.
No gas at main burners.
Check gas line for air, purge as necessary. A fter purging
gas line of air, allow gas to d issipate for at l east 5 minutes
before attempting to relight unit.
Check gas valve.
Water in gas line. Drain water and install drip leg to trap water.
No power to furnace. Check power supply, fuses, wiring, a nd circuit breaker.
No 2 4 v power supply t o control
circuit.
Check transformer. Transformers with internal overcurrent
protection require a cool down period before resetting.
Miswired or loose connections. Check all wiring and wire nut connections.
Burned---out h eat anticipator in
thermostat.
Replace thermostat.
Broken thermostat wires. Run continuity check. Replace wires, if n ec essary.
Inadequate Heating.
Dirty air filter. Clean or replace filter as necessary.
Gas input to unit too low.
Check gas pressure at manifold. Clock gas meter for input.
If too low, increase manifold pressure, or r eplace with
correct orifices.
Unit undersized for application. Replace with proper unit or add additional unit.
Restricted airflow. Clean filter, replace filter, or remove any r estrictions.
Blower speed too low.
Use high speed tap, increase fan speed, o r install optional
blower, as suitable for individual units.
Limitswitchcyclesmainburners.
Check rotation of blower, thermost at heat anticipator
settings, and temperature rise of u nit. Adjust as needed.
Too m uch outdoor air.
Adjust minimum position.
Check e conomizer o peration.
Poor Flame
Character i stics.
Incomplete com bustion (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.
Overfired unit — reduce inp ut, change orifices, or adjust
gas line or manifold pressure.
Check vent for restriction. Clean as necessary.
Check orifice to burner alignment.
Burners Will N ot Turn
Off.
Unit is locked into Heating mode
for a one minute minimum.
Wait until mandatory one---minute time period has elapsed
or reset p ower to unit.
48TC