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)?
No
Main incoming power not connected
Connect proper supply power to unit
Yes
Line voltage across T1 & T2,
T2 & T3, and T1 & T3 on main
disconnect (DS1)
No
Main disconnect (DS1) open or defective
Close, repair, or replace
Yes
24 VAC across R and C?
No
Main transformer (TR1) fault
Reset or replace main transformer
Yes
24 VAC across G and C?
No
Fan Switch (S2) open or not wired
Close or wire fan switch
(If fan switch is not required, place jumper from R to G)
Yes
Blank screen on
microprocessor controller?
Yes
Microprocessor controller defective or not powered
Replace or wire furnace controller
Unit Main
No
Furnace Board
Line voltage at primary side of
furnace transformer (TR5)?
No
Fuse (FU7) Blown
Test and replace blown fuse(s)
Yes
24 VAC across 20 and 101?
No
Fuse (FU9) Blown
Test and replace blown fuse
Furnace Transformer (TR5) fault
Replace heating transformer
Yes
24 VAC across C1 and G0 on
pCOe (SC1)?
No
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
Yes
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Summary of Contents for AR-DE12-05A
Page 75: ...Gas Supply In Typical Split Burner Manifold ...
Page 94: ...NOTE For HMA gas furnace for 311 and 352 chassis see separate IOM Manual ...
Page 96: ...HANDHELD KEYPAD DISPLAY OPTIONAL ...
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Page 130: ...Controls Sequence of Operation ...
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