SERVICING
54
Do
not
derate the furnace by adjusting the manifold pressure
to a lower pressure than specified on the furnace rating plate.
The combination of the lower air density and a lower manifold
pressure will prohibit the burner orifice from drawing the proper
amount of air into the burner. This may cause incomplete
combustion, flashback, and possible yellow tipping.
In some areas the gas supplier may artificially derate the gas
in an effort to compensate for the effects of altitude. If the
gas is artificially derated the appropriate orifice size must be
determined based on the BTU/ft
3
content of the derated gas
and the altitude. Refer to the National Fuel Gas Code, NFPA
54/ANSI Z223.1, and information provided by the gas supplier
to determine the proper orifice size.
CHECKING FOR DELAYED IGNITION
Delayed ignition is a delay in lighting a combustible mixture
of gas and air which has accumulated in the combustion
chamber.
When the mixture does ignite, it may explode and/or rollout
causing burning in the burner venturi.
If delayed ignition should occur, the following should be
checked. Furnace design makes this extremely unlikely
unless safety controls have been by-passed or tampered
with. Never by-pass or alter furnace controls.
1. Improper gas pressure - adjust to proper pressure (See
S-307 CHECKING GAS PRESSURE
).
2. Improper burner positioning - burners should be in locating
slots, level front to rear and left to right.
3. Carry over (lighter tube or cross lighter) obstructed - clean.
4. Main burner orifice(s) deformed, or out of alignment to
burner - replace.
CHECKING INTEGRATED IGNITION CONTROL
BOARDS
NOTE:
Failure to earth ground the furnace, reversing the
neutral and hot wire connection to the line (polarity), or a
high resistance connection in the neutral line may cause the
control to lockout due to failure to sense flame.
T
O
AVOID
TH
E R
IS
K
OF
E
L
EC
T
R
I
C
AL
SHO
CK
,
WI
R
ING
TO
TH
E
UNIT
MUST
B
E
P
R
OP
ER
LY
POLA
R
IZ
E
D
AND
G
R
OUND
E
D
.
D
IS
C
ONN
EC
T
POW
ER
B
E
FO
RE
P
ER
FO
R
MING
S
ER
VI
CE
LIST
E
D
B
E
LOW
.
WARNING
The ground wire must run from the furnace all the way back
to the electrical panel. Proper grounding can be confirmed by
disconnecting the electrical power and measuring resistance
between the neutral (white) connection and the burner closest
to the flame sensor. Resistance should be less than 2 ohms.
The ignition control is a combination electronic and
electromechanical device and is not field repairable. Complete
unit must be replaced.
L
IN
E
VOLTAG
E
NOW
P
RE
S
E
NT
WARNING
These tests must be completed within a given time frame due
to the operation of the ignition control. The trial for ignition
period is 4 seconds.
The ignition control is capable of diagnosing many furnace
failures to help in troubleshooting. The control utilizes a dual,
7-segment LED display to indicate diagnostic codes.
When the control is powered up normally the light will be on
continuously. The display will indicate
“ON”
when powered
and in standby mode. This can be used to test for 120 volts
and 24 volts to the control since both must be present for
the light to be on. If this step fails, check for 120 volts to the
control and check the transformer and its associated wiring.
If this step is successful give the control a call for heat and
wait five (5) seconds or until the furnace goes into lockout.
If the control detects a failure it will now be shown on the
diagnostic indicator light/display. Refer to the
Abnormal
Operation
section in the
Sequence of Operation
section of
this manual for more detail on failure codes.
1. Check for 120 volts from Line 1 (Hot) to Line 2 (Neutral)
at the ignition control. No voltage, check the door switch
connections and wire harness for continuity.
2. With the thermostat calling for heat, check for 24 volts
from W1 to C terminal on the ignition control. No voltage.
Check transformer, room thermostat, and wiring.
If you have 24 volts coming off the transformer but receive
approximately 13 volts on the terminal board between (C)
and (R), check for blown fuse.
3. Check for 120 volts to the induced draft blower (low-stage)
by measuring voltage between Pin 3 and Pin 4 (on the
5-pin connector) located on circuit board. No voltage,
check for loose connection in the 5-pin connector or
replace ignition control.
Check for 120 volts to the induced draft blower (high-
stage) by measuring voltage between Pin 2 and Pin 4 (on
the 5-pin connector) located on circuit board. No voltage,
check for loose connection in the 5-pin connector, no call
for high stage heat or replace ignition control.
4. If voltage is present in Steps 1 through 3 and the induced
draft blower is operating, check for 120 volts to the ignitor
during the preheat cycle. Measure voltage between Pin
1 and Pin 5 (on the 5-pin connector) located on ignition
control. No voltage, check low stage and high stage
pressure switches or replace the ignition control board.
5. After the ignitor warm-up time, begin checking for 24 volts
to the gas valve. Voltage will be present for seven seconds
only if proof of flame has been established.
6. If proof of flame was established voltage will be provided
to the air circulation blower following the heat on delay
period.
a. BEFORE replacing the ECM motor assembly or the
end bell, first check the motor with a Goodman #UTT-
