Flash Code Troubleshooting - York DM036 Installation Manual

5011492-XIM-B-0815
The furnace may shut down on a high tempera-
ture condition during the procedure. If this
occurs, the UCB energize the supply air blower
motor until the high temperature limit has reset.
Caution should be used at all times as the supply
air blower may energize regardless of the room
thermostat fan switch position.
Before beginning symptomatic troubleshooting activities read
the flash code LEDs on the unit control board (UCB) and the
ignition control board (ICB). Fault codes have a quick sequence
of flashes indicating the flash code number followed by a pause
with the LED off. The ICB flash codes are repeated until the
fault is cleared. The ICB monitors itself, the centrifugal switch,
lockout due to > 16 pilot flame losses, primary limit, rollout and
a flame present when the ICB expects no flame.
With power applied to the unit, if the LED on the ICB is flashing
the heartbeat and the furnace will not operate, then proceed to
the symptomatic troubleshooting section. If the ICB LED is not
flashing, then perform the ICB troubleshooting procedures. If
the ICB has a flash code other than the heartbeat, then
determine the flash code and locate its troubleshooting
procedures in the flash code troubleshooting section. Refer to
Table 27 for flash code identification and component causing
fault.

Flash Code Troubleshooting

Power to the unit should be interrupted during the
troubleshooting of individual components unless otherwise
indicated. All troubleshooting procedures assume the unit is
wired per the wiring diagram. If there is any indication the unit
has been previously repaired, then the first priority is to verify
that the furnace is wired per the wiring diagram. Miss-wired
units will give false flash codes.
Ignition Control Board
The ICB controls the ignition of the pilot, the opening and
closing of the gas valves and the operation of the draft (inducer)
motor. It also monitors all the furnace safety components.
If the ICB LED is on steady, then verify the wiring of the unit to
the wiring diagram and if ok, then replace the ICB. If the unit
has power and the ICB LED is not flashing, then remove the 3
pin connector (single stage gas heat) or 4 pin connector (2
stage gas heat) from the ICB. Measure the control voltage
between terminals 1 and 2 of the wiring harness connector. The
control voltage must be between 18 and 30 volts. If control
voltage is not present, then check the 3.2A circuit breaker to
verify that the circuit breaker has control voltage on both input
and output terminals. If control voltage is present on the input
and not the output of the circuit breaker, then reset or replace
the circuit breaker as necessary. If control voltage is present on
both sides of the circuit breaker, then check the power and
46
common wires between the unit control box and the ICB and
repair as necessary. If the control voltage is present, then verify
the cleanliness of the harness and the ICB connector, clean if
necessary and reconnect the wiring harness to the ICB and
observe ICB LED. If it now flashes the heartbeat, then the fault
was a bad connection between the harness connector and the
ICB connector or a broken wire exists in the harness. With the
harness connected to the ICB, gently move the wires in the
harness while observing the ICB LED. If heartbeat is steady,
then verify proper operation of the furnace. If the ICB does not
flash the heartbeat, then gently move the wires in the harness
connector while observing the ICB LED. If you get any flashes
of the ICB LED, then there is still a bad connection or a broken
wire. If no flashes are seen while gently moving the wires with
the harness connected to the ICB, then replace the ICB and
verify proper operation of the furnace.
Centrifugal Switch
The centrifugal switch is an integral part of the draft motor. The
centrifugal switch closes when the motor speed increases to
~2500 rpm and opens when the motor speed descends to
~2000 rpm.
If a flash code indicates the centrifugal switch is causing a fault,
then
1. If the flash code indicates the switch is open with the draft
(inducer) motor on (flash code 2), then
• Disconnect power to the unit. Using a screw driver,
spin the draft motor blower wheel. If bound or
dragging, then visually inspect the draft motor blower
wheel area for debris. If debris is present, then clear
debris and verify proper furnace operation. If clear,
then replace the draft motor and verify proper furnace
operation.
• Restore power to unit and induce a call for heat.
Measure the voltage across the two draft motor power
leads. If it is less than 342 volts, then check and repair
the power circuit to the draft motor. If the voltage is
greater than 342 volts and the draft motor is not
turning, then disconnect power and draft motor power
leads. Measure the resistance of the draft motor
windings. If an open circuit exists in the motor, then
replace the draft motor. If the voltage is greater than
342 volts and the motor is turning, then check the
centrifugal switch wiring between the ICB and the draft
motor. If ok, then disconnect power to the unit and
place the gas valve in the off position. Prepare to
temporarily jumper the wires connected to terminals 3
and 8 of the ICB 9 pin harness connector by
disconnecting the draft motor leads from the 9 pin
harness. Restore the power to the unit and induce a
call for heat. Jumper wires 3 and 8. If the ignition
sequence is started after 15 seconds (audible
sparking of the igniter), then replace the draft motor
reconnecting the centrifugal switch wiring per the
wiring diagram. If not, then replace the ICB, remove
the jumper and reconnect the centrifugal switch wiring
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