SERVICING
31
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.
Furnace design makes this extremely unlikely unless safety
controls have been by-passed or tampered with. Never by-
pass or alter furnace controls.
If delayed ignition should occur, the following should be
checked:
1. Improper gas pressure - adjust to proper pressure (See
CHECKING GAS PRESSURE
).
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.
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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 10 ohms.
The ignition control is a combination electronic and
electromechanical device and is not field repairable. Complete
unit must be replaced.
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These tests must be completed within a given time frame due
to the operation of the ignition control.
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. Check for 24 volts from W 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 by
measuring voltage between Pin 4 & 5 (black & white wire
on 5 pin connector.)
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.
5. After the ignitor warmup 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.
WARNING
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CHECKING FLAME SENSOR
1. Disconnect the yellow flame sensor wire from the sensor
2. Connect a micro-amp meter in series with this wire and
the sensor terminal.
3. Place the unit into a heating cycle.
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WARNING
4. As soon as flame is established a micro-amp reading
should be evident once proof of flame (micro-amp
reading) is established, the hot surface ignitor will be de-
energized.
5. The Integrated Ignition controls will have 2 - 4 uAmps.
Anything below .08 uAmps and the unit will shut down. If
the micro-amp reading is less than the minimum specified,
check for high resistance wiring connections, sensor to
burner gap, dirty flame sensor, or poor grounding.
6. If absolutely no reading, check for continuity on all
components and if good - replace ignition control module.
NOTE:
Contaminated fuel or combustion air can create a
nearly invisible coating on the flame sensor. This coating
works as an insulator causing a loss in the flame sense signal.
If this situation occurs the flame sensor must be cleaned with
steel wool.
