51
Dia
gn
ost
ics
FIGURE 33
DIAGNOSTICS FLOWCHART
GO TO
E
NOTE: Always verify gas valve inlet and outlet gas pressure.
KEY TO ABBREVIATIONS
IBM = Indoor Blower Motor
IDM = Induced Draft Motor
IFC = Integrated Furnace Control
PS = Pressure Switch(es)
SE = Spark Electrode
DSI = Direct-Spark Ignition
FLAME (AMBER) LED CODES
OFF = No Flame Present
RAPID BLINK = Unexpected Flame
SLOW BLINK = Marginal Flame Sense
STEADY ON = Normal Flame Sense
Does the IDM Energize?
IDM Runs for 30 sec. pre-purge ?
Spark Ignitor Sparking?
Does Main Burner Light and stay lit?
Is the gas valve energized?
PS dropping out ?
Check IFC*
Does IBM start on heat speed 20 seconds
after burners light ?
Does main burner remain lit until
heat call ends?
Does thermostat maintain reasonable room
temperature near setpoint ?
Set thermostat to off position (W to C = ØV)
Does gas valve shut off immediately?
Does IDM shut off after ten second post-purge?
Does IBM shut off after a max. of 3 min?
END
Heat-mode troubleshootin g
“FAULT DISPLAYED ?”
24V on W to IFC?
Check IFC*.
Does IDM run
indefinately .
Does IDM Run for 60 sec. and then off for Five minutes
- Check thermostat in “heat” mode,
battery, wire, and connections.
- Check PS contact s
- Check wires for short.
- Check IFC*.
- Check switches and hoses for
water or moistur e
- Check PS, PS Hoses, and wires.
- Check for blocked vent, excessive vent length or elbows, or
blocked heat exchanger .
- Check IDM wired correctly .
- Ensure against excessive wind, which can open pressure switch.
- Check for intermittent P.S. operation.
- Check switches and hoses for water or moisture.
- Check gas supply and manifold pressure.
- Ensure L1 and Neutral not swapped on IFC and junction box.
- Check igniter alignment .
- Check orifice or other restrictions to gas flo w.
- Check flame sense rod (clean with scotch brite pad).
- Check flame carry over.
- Check wires, continuity , and connection between IFC and gas valve.
- Ensure 24 V between appropriate pins on connector of IFC.
- Ensure manual switch on valve is in the “ON” position.
- 90+ check aux. limit open? Should be closed
- 90+ upflow models – check drain pressure switch between IFC and
gas valve – should be closed – replace drain pressure switch if drai n
is not blocked or clear drain if blocked.
- Did a pressure switch open during ignition trial? If yes, go to F
- Did a limit open during ignition trial? If yes, go to D
- Check line voltage between “HEAT” and “NEUTRAL” on IFC.
- Check wires, connections, and continuity between IFC and IBM.
- Check IBM capacitor .
- Check IBM.
CHECK:
- grounding on IFC and unit.
- check for proper polarity between L1 & neutral.
- flame sense rod (clean if necessar y).
- wire continually between flame sense rod and appropriate pin of
connector on IFC
- flame carries across all burners, and all burners stay lit.
CHECK:
AIRFLOW - ensure no restrictions, such as dirty filte r, dampers, closed registers, etc.
LIMITS - ensure good wire and connections between IFC and all limits. Make sur e
limits are not open when circulating air temperature is within a specified range.
ROLLOUTS - ensure rollouts or overtemperature limits do not need to be reset. Make
sure no flame rollout in burner compartment due to blocked flu or heat exchanger .
OVERFIRE - ensure furnace is not overtemperature (temp rise is above stated range) .
Check gas valve, proper orifice size, gas pressure, etc.
Is Limit circuit open or opening and closing?
Note: IFC Status LED should be blinking a Fault Code.
Is the IFC sensing a good flame: NOTE:
Flame sense light should be steady-on
when burners are lit. If flame LED blinking,
or off, flame sense is low or absent.
Ensure thermostat is properly placed and not improperly affected by
registers, fans, sunlight, heat through walls, pipes, or wires in walls .
- Check heat anticipator setting. Furnace may need an isolation relay.
- Check installation instructions under section titled “Isolation Relay” for
details .
- Verify correct furnace sizing.
NOTE: If IFC goes into lockout (“ST ATUS LED will blink code “1”), shut
off main power to unit, wait 30 seconds and then reset power .
PROBLEM
STILL
PRESENT
Fault Code Present
“FLAME” LED BLINKING
OR STEADY ON
If “E” did not
resolve issue
Double check - Is W off at IFC?
(W to C = ØV?)
Voltage present at gas valve?
- Check gas valve.
SEE FAULT CODES
- Check IFC*.
Check IFC*.
*Most failures are not due to the IFC. Doubl e
check all other possibilities, including the
ground connection or wire connections, before
replacing the IFC.
Ensure TSTAT is not in “FAN” position.
Is disply flashing a fault code
Is “FLAME” LED blinking or steady-on ?
**System will attempt to light 4 times. Voltage
is present at gas valve for only 7 seconds dur -
ing each trial for ignition. The entire system will
go into a 1 hour lockout after 4 attempts.
- Check line voltage at IDM.
- Check wires and connections between IDM and IFC.
- Ensure line voltage on IDM pins of IFC connector .
- Check IDM capacitor (90+ only) .
CHECK BLINK CODES
- Check for open limit or limit circuit.
FOR DIRECT SPARK IGNITION
- Check ignitor connected .
- Check ignitor wires.
- Check ignitor for fractures or cracking
- Check ignitor placement .
- If problem persists, check IFC*.
REPEAT THIS PROCEDURE UNTIL TROUBLE-FREE OPERATION IS OBTAINED.
1) Set FAN switch to “AUTO”
2) Set thermostat to call for low HT ( “W” terminal)
START
YES
NO
NO
If “I ” did not
resolve issue.
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
I
D
F
E
G
YES
NO
YES
PREPURGE
IGNITION TRIAL
IBM “ON” DELAY
STEADY STATE LOW HT
END HEAT CALL
POST-PURGE
IBM “OFF” DELAY
STEADY OFF
NO
**
ST-A1227-08-00
GO TO
F
GO TO
I
W
A
R
N
IN
G
H
A
ZA
R
D
O
U
S
V
O
LT
A
G
E
LI
N
E
V
O
LT
A
G
E
C
O
N
N
E
C
TI
O
N
S
D
IS
C
O
N
N
E
C
T
P
O
W
E
R
B
E
FO
R
E
S
E
R
V
IC
IN
G
.
S
E
R
V
IC
E
M
U
S
T
B
E
B
Y
A
T
R
A
IN
E
D
,
Q
U
A
LI
FI
E
D
S
E
R
V
IC
E
T
E
C
H
N
IC
IA
N
.
N
O
TE
:A
lw
ay
s
ve
rif
y
ga
s
va
lv
e
in
le
t
an
d
ou
tle
t
ga
s
pr
es
su
re
.
IN
TE
G
R
A
TE
D
F
U
R
N
A
C
E
C
O
N
TR
O
L
(IF
C
)
D
IA
G
N
O
S
TI
C
S
G
U
ID
E
N
O
TE
: M
os
t
fa
ilu
re
s
ar
e
no
t
du
e
to
t
he
I
FC
.
D
ou
bl
e
ch
ec
k
al
l
ot
he
r
po
ss
ib
ili
tie
s,
in
cl
ud
in
g
th
e
gr
ou
nd
co
nn
ec
tio
n,
be
fo
re
re
pl
ac
in
g
th
e
IF
C
.
BLOCKED DRAIN - (fault “59” should be present)
Set T-stat to High Heat - Energize W2 + W
Fault
Priority
24
22
21
19
23
13
15
14
16
2
20
4
17
3
6
9
8
7
11
18
1
CODE
DESCRIPTION
O
C
H
h
F
10
11
12
13
14
20
22
26
33
44
46
45
55
57
61
93
Standby
Compressor on (cooling or heat pump heat)
High Gas heat on
Low gas heat on
Continuous fan on
1 Hour lockout
Failed ignition
Low flame sense
Flame lost
Unexpected flame
Twinning fault
Main limit open
Line and Neutral reversed
MRLC(Man. Reset limit cont.)(aka roll-out) open
Low Pres. Switch Closed
Low Pres. Switch Open, Indcr on low Speed
Low Pres. Switch Open, Indcr on High Speed
High Pres. Switch Closed
High Pres. Switch Open
Blower Fault - blower unable to run
Internal control fault
“ATTEND TO FAULT”
- For Twinned units, check that both IFCs are set for “TWIN” and wire s
are connected between “TWIN” terminals .
- Check IFC*.
- For twinned units, ensure transformers are in phase.
(if out of phase, flame LED will be dim) .
- For non-twinned units, ensure “TWIN” is in the single (OFF) position.
- For Twinned units – ensure both IFC‘s have same part number .
H
Check for high gas valve relay
on IFC stuck closed. Replace
IFC, if neccessary
Do IDM, IBM & Gas Valve Shift to High Heat?
STEADY HIGH HEAT
CHECK:
-IDM
-IDM Capacitor
-Low Pres. Sw. wiring
-Hoses to Low Pres. Sw.
CHECK:
-IBM
-IBM Capacitor
-Wiring
-Flame Sense Rod
Low Pressure
Switch Open?
High Gas Valve
Energized?
24 VAC on
W2?
Check
T- STAT
NO
NO
NO
NO
YES
YES
YES
YES
YES
Restore thermostat to
normal operation.
