SERVICING
54
Do derate the furnace by adjusting the manifold pressure
The combination of the lower air density and a lower manifold
amount of air into the burner. This may cause incomplete
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
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.
burner - replace.
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
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ERE ERR ERCE E E.
The ground wire must run from the furnace all the way back
disconnecting the electrical power and measuring resistance
between the neutral (white) connection and the burner closest
The ignition control is a combination electronic and
unit must be replaced.
E E REE
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 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
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.
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
to the air circulation blower following the heat on delay
period.
a. BEFORE replacing the ECM motor assembly or the
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