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29733 R2 06/01/2003
39
TABLE C-4: SYSTEM & GENERAL TROUBLESHOOTING, continued from previous page
Problem Possible Cause Remedy
Airflow blocked or dirty air
filter.
Clean or replace air filter.
Thermostat adjustments
or location.
Check thermostat heat anticipator setting against
measured amperage draw. Increase heat anticipator
setting if necessary. If the thermostat is being influenced
by drafts, sunlight, duct work, etc., relocate to more
suitable location.
Insufficient airflow.
Check all dampers. Open closed dampers including
registers in unused rooms. Check system temperature
rise. If temperature rise is too high, speed up blower fan.
Defective high limit
control.
Test high limit function of all limit switches. Use a duct
thermometer to assess accuracy of limit control. Check
for obstructions to airflow around limit switch bi-metal
elements. Replace control if necessary.
Under-sized nozzle.
Check nozzle. If problem is not caused by air flow
problems, use larger nozzle, if permitted by rating plate.
Blower fan motor
stopping intermittently on
overload.
Check blower fan motor amperage draw. Check motor
ventilation ports, clean if necessary. Replace motor if
necessary.
Furnace will not warm
home to desired
temperature.
Burner motor stopping
intermittently on overload.
Check burner motor. Replace if necessary.
Home does not heat
evenly
Improper distribution of
heat.
This is not likely to be a furnace problem. Balance duct
system.
Airflow blocked or dirty air
filter.
Clean or replace air filter.
Supply air
temperature too hot.
Insufficient airflow.
Check all dampers. Open closed dampers including
registers in unused rooms. Check system temperature
rise. If temperature rise is too high, speed up blower fan.
Excess airflow.
Check system temperature rise. Slow down blower fan if
necessary.
Supply air
temperature too cool.
Excessive duct losses.
Check supply air ductwork. Seal leaky joints and seams.
Insulate ductwork if necessary.
Fan control "fan on"
setting too low.
Increase differential between fan control "fan off" and
"fan on" settings. (L4064B, L6064A fan / limit controls
only, no adjustments available for L4064W fan / limit
control). Register air deflectors may help.
Supply air
temperature too cool
during first moments
of furnace cycle.
Excessive duct losses.
Check supply air ductwork. Seal leaky joints and seams.
Insulate ductwork if necessary.