LG GEN2 Series Installation And Operation Manual page 81

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.
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
Supply fan running?
Yes
24 VAC across W1 and C?
Yes
24 VAC across A2 and A1
on the RH relay?
Yes
Unit Main
Furnace Board
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Main incoming power not connected
No
Main disconnect (DS1) open or defective
No
No
No
(If fan switch is not required, place jumper from R to G)
No
Push reset button on overload or VFD to reset.
Check motor amp draw and correct as necessary
Damper limit switch (D1L) not closed -
Damper stuck closed or actuator failed
Repair damper interference or replace actuator
Exhaust fan contactor not powered
Close or wire exhaust switch, reset exhaust overload, or replace faulty
No
(If heat switch is not required, place jumper from R to W1)
No
Connect proper supply power to unit
Close, repair, or replace
Main transformer (TR1) fault Reset
or replace main transformer Phase
Monitor (PM) Contact Open Correct
incoming phase order
Fuse (FU6) Blown
Test and replace blown fuse(s)
Fan Switch (S2) open or not wired
Close or wire fan switch
Freeze protection tripped
Cycle disconnect to reset
Supply fan overload tripped
exhaust contactor.
Heat Switch (S4) open or not wired
Close or wire heat switch
Starter interlock (ST1) not closed
Replace contactor