Lennox G50UHX Series User Manual

Page 39
PROBLEM 1: UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE
Condition Possible Cause Corrective Action / Comments
1.5
− On initial power−up the combustion
air blower remains energized.
Di ti li ht fl h th i
1.5.1
Improper ground to the unit.
ACTION 1 − Check that the unit is properly
ground.
ACTION 2 − Install a proper main ground to the
unit
g
− Diagnostic lights flash the improper
main ground.
1.5.2
6−Pin connector is improperly at-
tached to the circuit board.
ACTION 1 − Check 6−pin connector for proper
installation. Correctly insert connector into con-
trol.
LED#1−Alternating Fast Flash
LED#2−Alternating Fast Flash
1.5.3
Line voltage is below 75V.
ACTION 1 − Check that the line voltage is above
75V. Determine cause of voltage drop and supply
correct voltage to the control.
PROBLEM 2: UNIT FAILS TO OPERATE IN THE COOLING OR HEATING MODE, BUT COMBUSTION
AIR INDUCER OPERATES CONTINUOUS. UNITS WITH CONTROL BOARDS DATE CODED AFTER
NOV. 1 1997, WILL OPERATE IN COOLING BUT NOT IN THE HEATING MODE, WITH COMBUSTION
AIR INDUCER CYCLING 5 SECONDS ON 55 SECONDS OFF.
Condition Possible Cause Corrective Action / Comments
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
2.1.1
Open ignitor circuit.
ACTION 1 − Check for correct wiring and loose
connections in the ignitor circuit. Check mult−
plug connections for correct installation.
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
2.1.2
Broken or failed ignitor.
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.
PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES
NOT ENERGIZE
Condition Possible Cause Corrective Action / Comments
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
d
3.1.1
Primary or secondary (if equipped )
limit open.
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.
gg
mode.
LED#1−Slow Flash,
LED#2−On
3.1.2
Miswiring of furnace or improper con-
nections at limit switch(es).
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
3.2
− Unit operates with a cooling and con-
tinuous fan demand.
− Combustion air inducer will not start
with a Heating demand.
− Dia
g
nostic li
g
hts flash the
p
ressure
3.2.1
Miswiring of furnace or improper con-
nections to combustion air inducer.
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
−
Diagnostic
lights
flash
the
pressure
switch failure code.
LED#1−Off,
LED#2−Slow Flash
3.2.2
Prove switch stuck closed.
ACTION 1 − Check that the pressure switch is
open without the combustion air inducer operat-
ing. Replace if defective.

Lennox G50UHX Series Specifications

General

Brand	Lennox
Model	G50UHX Series
Category	Furnace
Language	English