22
Table C-3: System and General Troubleshooting
continued
Problem Possible
Cause
Remedy
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.