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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.
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.
w
t
a
eat
ng
eman
.
– 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 instructions.
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.
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