3DJH
PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES
NOT ENERGIZE (CONT.).
Condition
Possible Cause
Corrective Action/Comments
3.3
- Unit operates with a cooling and
continuous fan demand.
- Combustion air blower will not
start with a Heating demand.
- Diagnostic lights flash the pres-
sure switch failure code 2.5 minutes
3.3.1
Miswiring of furnace or improper
connections to combustion air
blower.
ACTION 1 - Check for correct wiring and loose
connections. Correct wiring and/or replace
any loose connections.
sure switch failure code 2.5 minutes
after heating demand.
LED#1-Off,
LED#2-Slow Flash
3.3.2
Combustion air blower failure.
ACTION 1 - If there is 120V to combustion air
blower and it does not operate, replace com-
bustion air blower.
PROBLEM 4: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER
ENERGIZES, IGNITOR IS NOT ENERGIZED.
Condition
Possible Cause
Corrective Action/Comments
4.1
- Unit operates with a cooling and
continuous fan demand.
- Combustion air blower energizes
with a heating demand
4.1.1
Pressure switch does not close
due to incorrect routing of the
pressure switch lines.
ACTION 1 - Check that the pressure switch
lines are correctly routed. Correctly route
pressure switch lines.
with a heating demand.
- Diagnostic lights flash the pres-
sure switch failure code 2.5 min-
utes after heating demand.
4.1.2
Pressure switch does not close
due to obstructions in the pressure
lines.
ACTION 1 - Remove any obstructions from
the the pressure lines and/or taps.
LED#1-Off
LED#2-Slow Flash
4.1.3
Pressure switch lines damaged
ACTION 1 - Check pressure switch lines for
leaks. Replace any broken lines.
LED#2 Slow Flash
4.1.4
Condensate in pressure switch
line.
ACTION 1 - Check pressure switch lines for
condensate. Remove condensate from lines.
Check that the condensate lines are located
correctly.
4.1.5
Pressure switch does not close
due to a low differential pressure
across the pressure switch.
ACTION 1 - Check the differential pressure
across the pressure switch. This pressure
should exceed the set point listed on the
switch.
ACTION 2 - Check for restricted inlet and
exhaust vent. Remove all blockage.
ACTION 3 - Check for proper vent sizing
and run length. See installation instruc-
tions.
4.1.6
Wrong pressure switch installed in
the unit, or pressure switch is out
of calibration.
ACTION 1 - Check that the proper pressure
switch is installed in the unit. Replace pres-
sure switch if necessary.
4.1.7
Miswiring of furnace or improper
connections at pressure switch.
ACTION 1 - Check for correct wiring and loose
connections. Correct wiring and/or replace
any loose connections.
4.1.8
Pressure switch failure.
ACTION 1 - If all the above modes of failure
have been checked, the pressure switch may
have failed. Replace pressure switch and de-
termine if unit will operate.