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.
...continued from previous page
Fuse (FU8) Blown
Test and replace blown fuse
Furnace Transformer (TR5) fault
Replace heating transformer
120 VAC at 120/240 terminal on
Ignition Controller (IC#)?
No
Yes
Pressure switch tubing kinked, disconnected,
plugged, or filled with water/ice.
Straighten, connect, clear or replace pressure switch tubing
Pressure switch (PS2) failure
Repair or replace pressure switch (PS2)
Combustion blower (CM) not functioning
Replace fusing (FU7), combustion blower or relay (CM)
Ignition Controller (IC#) red LED
blinks 6 times
or
Microprocessor Alarm:
‘Combustion fan not proved’?
Yes
No
Combustion blower operating with no call for heat to
ignition controller
Check wiring to combustion fan and correct as necessary
Ignition Controller (IC#) BLWR relay fault (relay stuck closed)
Replace ignition controller
Pressure switch (PS2) failure
Repair or replace pressure switch (PS2)
Microprocessor Alarm:
‘Pressure Switch closed
with combustion fan off’?
Yes
No
Microprocessor Alarm:
‘IG furnace high pressure’?
Yes
Pressure switch tubing kinked, disconnected,
plugged, or filled with water/ice.
Straighten, connect, clear or replace pressure switch tubing
Pressure switch (PS5) failure
Repair or replace pressure switch (PS5)
Combustion blower (CM) not functioning
Replace fusing (FU7), combustion blower or relay (CM)
No
24 VAC between 24 VAC
terminals on mod valve?
No
Yes
Connection fault between terminal 20 and mod valve
Check and repair connection issue
Does the 0-10 VDC signal at the
SIG+/- terminals on the mod
valve correspond to the heat %
shown on the controller?
No
Connection fault between pCOe and mod valve
Check and repair connection issue
Microprocessor controller or pCOe defective
Replace defective parts
Yes
Continues on next page...
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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