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 andloose
connections. Correct wiring and/or replace
any loose connections.
sure switch failure code 2
.
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
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.
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 andloose
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.
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