LG AR-DE12-05A, Installation And Operation Manual

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Troubleshooting - 4:1 Modulating Furnace
4:1 Modulating Furnace with Stand-Alone Controller Will Not Light
In all cases, verify correct terminals as shown on the unit-specific wiring diagram.
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Pressure switch tubing kinked, disconnected, plugged, or
filled with water/ice.
Straighten, connect, clear or replace pressure switch tubing
Pressure switch (PS5) failure
Repair or replace pressure switch (PS5)
Combustion blower (CM) not functioning
Replace fusing (FU7), combustion blower or relay (CM)
Furnace Controller Alarm:
‘High Speed PSW Fault’?
Yes
No
24 VAC between 24 VAC
terminals on mod valve?
No Connection fault between terminal 20 and mod valve
Check and repair connection issue
Yes
Does the 0-10 VDC signal at the
SIG+/- terminals on the mod
valve correspond to the heat %
shown on the controller?
No
Connection fault between pCOe and mod valve
Check and repair connection issue Furnace
controller defective
Replace defective parts
Yes
Manual supply gas valve off or combo valve (MV) switch turned off
Turn supply gas valve or combo valve on
Inlet gas pressure incorrect
Adjust inlet gas pressure to the range specified on the furnace label
Improper manifold pressure
Set high and low manifold pressure
(refer to 4:1 Electronic Modulation Start-Up section)
Faulty spark rod or spark gap does not equal 1/8 inch
Replace spark rod or adjust gap to 1/8 inch
Spark wire or connections faulty Repair
connections or replace wire
Flame sensor faulty, grounded, or faulty connection to
flame sensor
Replace or unground flame sensor or repair connection
Ignition Controller (IC#) red LED
blinks 1 time, 2 times or 4 times
or
Furnace Controller Alarm:
‘No flame 3 trials’?
Yes
No
Flame lights but doesn’t
travel all the way across
the burner manifold
Yes
No
Flame spread gap on outlet of burner pinched or blocked
Spread gap or remove debris
One or more orifices fully or partially plugged
Inspect and clean or replace orifices
Flame flashes back
during light off?
Yes
No
Heat exchanger cracked
Inspect and replace heat exchanger if necessary
Combustion air inlet or discharge passageway restricted
Inspect and remove restriction
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