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.
Line voltage across L1 & L2,
L2 & L3, and L1 & L3 on main
No
disconnect (DS1)?
Main incoming power not connected
Connect proper supply power to unit
Yes
Line voltage across T1 & T2,
T2 & T3, and T1 & T3 on main
No
disconnect (DS1)
Main disconnect (DS1) open or defective
Close, repair, or replace
Yes
24 VAC across R and C?
No
Yes
24 VAC across G and C?
No
Yes
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
(If fan switch is not required, place jumper from R to G)
Supply fan running?
No
Yes
24 VAC across W1 and C?
No
Yes
Freeze protection tripped
Cycle disconnect to reset
Supply fan overload tripped
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
exhaust contactor.
Heat Switch (S4) open or not wired
Close or wire heat switch
(If heat switch is not required, place jumper from R to W1)
24 VAC across A2 and A1
No
on the RH relay?
Starter interlock (ST1) not closed
Replace contactor
Unit Main
Furnace Board
Yes
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