Lennox G24M SERIES Unit Information page 32

PROBLEM 1: UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE
Condition
1.5
On initial power--up the combus-
- -
tion air blower remains energized.
Diagnostic lights flash the im- Di ti li ht fl h th i
- -
proper main ground.
LED#1--Alternating Fast Flash
LED#2--Alternating Fast Flash
PROBLEM 2: UNIT OPERATES IN COOLING MODE BUT NOT IN THE HEATING MODE, WITH
COMBUSTION AIR BLOWER CYCLING 5 SECONDS ON 55 SECONDS OFF.
Condition
2.1
On initial power--up the combus-
- -
tion air blower remains energized.
Diagnostic lights flash the im
- -
proper main ground.
-- Combustion air blower cycles 5 Combustion air blower cycles 5
seconds on 55 seconds off.
LED#1--Alternating Fast Flash
LED#2--Alternating Fast Flash
PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES
Condition
3.1
Unit operates with a cooling or
- -
continuous fan demand.
Combustion air blower will not
- -
start with a Heating demand.
-- Diagnostic lights flash the limit
failure mode. failure mode
LED#1--Slow Flash,
LED#2--On
3.2
-- 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. sure switch failure code
LED#1--Off,
LED#2--Slow Flash
Possible Cause
Improper ground to the unit.
g
6--Pin connector is improperly at-
tached to the circuit board.
Line voltage is below 75V.
Possible Cause
Open ignitor circuit.
Broken or failed ignitor.
NOT ENERGIZE
Possible Cause
Primary or secondary (if equipped)
limit open.
Miswiring of furnace or improper
connections at limit switch(es).
Miswiring of furnace or improper
connections to combustion air
Pressure switch stuck closed.
1.5.1
1.5.2
1.5.3
2.1.1
2.1.2
3.1.1
3.1.2
3.2.1
blower.
3.2.2
3DJH 
Corrective Action / Comments
ACTION 1 - - Check that the unit is properly
ground.
ACTION 2 - - Install a proper main ground to
the unit
ACTION 1 - - Check 6- -pin connector for proper
installation. Correctly insert connector into
control.
ACTION 1 - - Check that the line voltage is
above 75V. Determine cause of voltage drop
and supply correct voltage to the control.
Corrective Action / Comments
ACTION 1 - - Check for correct wiring and
loose connections in the ignitor circuit. Check
mult- -plug connections for correct installa-
tion.
ACTION 1 - - Unplug ignitor and read resis-
tance across ignitor. If resistance does not
read between 10.9 and 19.7 ohms, replace the
ignitor.
Corrective Action / Comments
ACTION 1 - - Check continuity
switch(es). Switches reset
upon cool down.
ACTION 2 - - Check for restrictions on blower
inlet air (including filter) and outlet air. Deter-
mine cause for limit activation before placing
unit back in operation.
ACTION 1 - - Check for correct wiring and
loose connections. Correct wiring and/or re-
place any loose connections.
ACTION 1 - - Check for correct wiring and
loose connections. Correct wiring and/or re-
place any loose connections.
ACTION 1 - - Check that the pressure switch is
open without the combustion air blower op-
erating. Replace if malfunctioning
across
automatically