Lennox G50UHi Unit Information page 29

PROBLEM 1: UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE
Condition
1.5
− On initial power−up the combustion
air blower remains energized. g
− Diagnostic lights flash the improper Di ti li ht fl h th i
main ground.
LED#1−Alternating Fast Flash
LED#2−Alternating Fast Flash
PROBLEM 2: UNIT WILL OPERATE IN COOLING BUT NOT IN THE HEATING MODE, WITH COM-
BUSTION AIR INDUCER CYCLING 5 SECONDS ON 55 SECONDS OFF.
Condition
2.1
− On initial power−up the combustion
air inducer remains energized.
− Diagnostic lights flash the improper
main ground.
− Units with control boards date
coded after Nov.1 1997; combustion coded after Nov 1 1997; combustion
air inducer will cycle 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 NOT
Condition
3.1
− Unit operates with a cooling or contin-
uous fan demand.
− Combustion air inducer will not start
with a Heating demand.
− Diagnostic lights flash the limit failure g g
mode. d
LED#1−Slow Flash,
LED#2−On
3.2
− Unit operates with a cooling and con-
tinuous fan demand.
− Combustion air inducer will not start
with a Heating demand.
− Diagnostic lights flash the pressure − Diagnostic lights flash the pressure
switch failure code.
LED#1−Off,
LED#2−Slow Flash
Possible Cause
1.5.1
Improper ground to the unit.
1.5.2
6−Pin connector is improperly at-
tached to the circuit board.
1.5.3
Line voltage is below 75V.
Possible Cause
2.1.1
Open ignitor circuit.
2.1.2
Broken or failed ignitor.
ENERGIZE
Possible Cause
3.1.1
Primary or secondary (if equipped )
limit open.
3.1.2
Miswiring of furnace or improper con-
nections at limit switch(es).
3.2.1
Miswiring of furnace or improper con-
nections to combustion air inducer.
3.2.2
Prove switch stuck closed.
Page 29
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 con-
trol.
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 multi−
plug connections for correct installation.
ACTION 1 − Unplug ignitor and read resistance
across ignitor. If resistance does not read be-
tween 10.9 and 19.7 ohms, replace the ignitor.
Corrective Action / Comments
ACTION 1 − Check continuity across switch(es).
Switches reset automatically upon cool down.
ACTION 2 − Check for restrictions on blower inlet
air (including filter) and outlet air. Determine
cause for limit activation before placing unit back
in operation.
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
ACTION 1 − Check that the prove switch is open
without the combustion air inducer operating. Re-
place if defective.