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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. 41.) Set
the outdoor--air thermostat 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. 41 -- OATL Connections
Troubleshooting Heating System
Refer to Table 13 and 14 for additional troubleshooting
topics.
Table 13 – Heating Service Analysis
PROBLEM CAUSE REMEDY
Burner s Will Not Ignite.
Misalign ed spa rk electrod es.
Check flame ignition and sensor electrode positioning.
Adjust as needed.
No gas at main burner s.
Check gas line for air, purge as necessary. After purging
gas line of air, allow gas to dissipa te for at least 5 minutes
before attemptin g 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, and circuit breaker.
No 24 v power suppl y to contr ol
circuit.
Check transformer. Transformers with internal overcurrent
protection require a cool down period before resetting.
Miswired or loose connecti o ns. Check all wiring and wire nut connections.
Burne d---out heat ant icipator in
thermostat.
Repl ace thermostat.
Broken thermo stat wires. Run continuity check. Replace wires, if necessary.
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 replace with
correct orifices.
Unit undersized for application. Replace with proper unit or add additional unit.
Restricted airflow. Clean filter, replace filter, or remove any restrictions.
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, ther mostat heat anticipator
settings, and temperature rise of un it. Adjust as needed.
Too much outdoor air.
Adjust minimum position.
Check economizer operation.
Poor Flame
Character i stics.
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.
Overfi red unit — reduce input, change orifices, or adjust
gas line or manifold pressure.
Check vent for restric t io n. Clean as necessary.
Check o rifice to burner alignment.
Burne rs Will Not Turn
Off.
Unit is locked into Heating mode
for a one minute minimum.
Wait until mandato ry one---minute time period has elapsed
or reset power to unit.
580J