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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 inducer energizes
with a heating demand
4.1.1
Pressure switch does not close due
to incorrect routing of the pressure
switch line.
ACTION 1 −
Check that the pressure switch line
is correctly routed. Correctly route pressure
switch line.
with a heating demand.
− Diagnostic lights flash the pressure
switch failure code 2.5 minutes after
heating demand.
4.1.2
Pressure switch does not close due
to obstructions in the pressure switch
line.
ACTION 1 −
Remove any obstructions from the
the pressure switch line and/or taps.
LED#1−Off
LED#2−Slow Flash
4.1.3
Pressure switch line damaged
ACTION 1 −
Check pressure switch line for leaks.
Replace broken line if required.
LED#2 Slow Flash
4.1.4
Condensate in pressure switch line.
ACTION 1 −
Check pressure switch line for con-
densate. Remove condensate from line.
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 vent. Re-
move 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 cal-
ibration.
ACTION 1 −
Check that the proper pressure
switch is installed in the unit. Replace pressure
switch if necessary.
4.1.7
Miswiring of furnace or improper con-
nections 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 determine if
unit will operate.
