Lennox G24M SERIES Unit Information page 33

PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES
Condition
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 sure switch failure code 2.5 minutes
after heating demand.
LED#1--Off,
LED#2--Slow Flash
PROBLEM 4: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER
Condition
4.1
Unit operates with a cooling and
- -
continuous fan demand.
Combustion air blower ener-
- -
gizes with a heating demand gizes with a heating demand.
-- Diagnostic lights flash the pres-
sure switch failure code 2.5 min-
utes after heating demand.
LED#1--Off
LED#2--Slow Flash LED#2 Slow Flash
NOT ENERGIZE (CONT.).
Possible Cause
Miswiring of furnace or improper
connections to combustion air
blower.
Combustion air blower failure.
ENERGIZES, IGNITOR IS NOT ENERGIZED.
Possible Cause
Pressure switch does not close
due to incorrect routing of the
pressure switch lines.
Pressure switch does not close
due to obstructions in the pressure
lines.
Pressure switch lines damaged
Pressure switch does not close
due to a low differential pressure
across the pressure switch.
Wrong pressure switch installed in
the unit, or pressure switch is out
of calibration.
Miswiring of furnace or improper
connections at pressure switch.
Pressure switch failure.
3DJH 
3.3.1
3.3.2
4.1.1
4.1.2
4.1.3
4.1.4
4.1.5
4.1.6
4.1.7
Corrective Action/Comments
ACTION 1 - - Check for correct wiring and
loose connections. Correct wiring and/or re-
place any loose connections.
ACTION 1 - - If there is 120V to combustion air
blower and it does not operate, replace com-
bustion air blower.
Corrective Action/Comments
ACTION 1 - - Check that the pressure switch
lines are correctly routed. Correctly route
pressure switch lines.
ACTION 1 - - Remove any obstructions from
the the pressure lines and/or taps.
ACTION 1 - - Check pressure switch lines for
leaks. Replace any broken lines.
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.
ACTION 4 - - Check voltage to thre combus-
tion air blower.
ACTION 1 - - Check that the proper pressure
switch is installed in the unit. Replace pres-
sure switch if necessary.
ACTION 1 - - Check for correct wiring and
loose connections. Correct wiring and/or re-
place any loose connections.
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.