LG GEN2 Series Installation And Operation Manual page 86

Troubleshooting - 4:1 or High Turndown Modulating Furnace
4:1 or High Turndown Modulating Furnace with Microprocessor Controller Will Not Light In all
cases, verify correct terminals as shown on the unit-specific wiring diagram.
Line voltage across L1 & L2,
L2 & L3, and L1 & L3 on main
disconnect (DS1)?
Yes
Line voltage across T1 & T2,
T2 & T3, and T1 & T3 on main
disconnect (DS1)
Yes
24 VAC across R and C?
Yes
24 VAC across G and C?
Yes
Blank screen on
microprocessor controller?
No
Unit Main
Furnace Board
Line voltage at primary side of
furnace transformer (TR5)?
Yes
24 VAC across 20 and 101?
Yes
24 VAC across C1 and G0 on
pCOe (SC1)?
Yes
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No
Main disconnect (DS1) open or defective
No
No
No
(If fan switch is not required, place jumper from R to G)
Microprocessor controller defective or not powered
Yes
No
No
Discharge temperature was above high limit control (HLC)
No
High limit control (HLC) does not close when at room temperature
Main incoming power not connected
Connect proper supply power to unit
Close, repair, or replace
Main transformer (TR1) fault
Reset or replace main transformer
Fan Switch (S2) open or not wired
Close or wire fan switch
Replace or wire furnace controller
Fuse (FU7) Blown
Test and replace blown fuse(s)
Fuse (FU9) Blown
Test and replace blown fuse
Furnace Transformer (TR5) fault
Replace heating transformer
Wait for high limit to cool and reset
Replace high limit control