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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Line voltage at primary side of
furnace transformer (TR5)?
No
Fuse (FU7) Blown
Test and replace blown fuse(s)
Yes
Fuse (FU9) Blown
Test and replace blown fuse
Furnace Transformer (TR5) fault
Replace Heating Transformer
24 VAC across 20 and 101?
No
Yes
Discharge temperature was above high limit control (HLC)
Wait for high limit to cool and reset
High limit control (HLC) does not close when at room temperature
Replace high limit control
24 VAC across C1 and G0 on
furnace controller (SC1)?
No
Yes
Blank screen
on furnace controller?
Yes
Furnace controller defective or not powered
Replace or wire furnace controller
No
Furnace Controller Alarm:
‘Furn Alarm - Check Log’?
Yes
New furnace alarm(s) have been logged
Press the down arrow to scroll to the end of the alarms menu.
Press enter to go to the data logger and review alarms.
No
Furnace Controller Alarm:
‘Supply Sensor (U2) Err’?
Yes
Discharge air sensor (U2) not wired or defective
Wire or replace discharge air sensor (U2)
No
Furnace Controller Alarm:
‘Inlet Sensor (U1) Err’?
Yes
Inlet air sensor (U1) not wired or defective
Wire or replace outdoor temperature sensor (U1)
No
Inlet air temperature above
heating lockout setting?
Yes
Increase heating lockout setting to above inlet air temperature
(Be sure to return this setting to the proper temperature
after testing furnace)
No
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