362247-BIM-B-0109
58 Johnson Controls Unitary Products
code troubleshooting section. Refer to Table 37 for flash
code identification and component causing fault.
FLASH CODE TROUBLESHOOTING
Power to the unit should be interrupted during the trou-
bleshooting of individual components unless otherwise
indicated. All troubleshooting procedures assume the
unit is wired per the wiring diagram. If there is any indi-
cation 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 flash-
ing, 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 volt-
age 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 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 connec-
tion between the harness connector and the ICB con-
nector 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 caus-
ing a fault, then
1. If the flash code indicates the switch is open with
the draft (inducer) motor on (flash code 2), then
a. 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 fur-
nace operation. If clear, then replace the draft
motor and verify proper furnace operation.
b. Restore power to unit and induce a call for heat.
Measure the voltage across the two draft motor
leads (white and red on single stage models and
white and black on two stage models). If it is less
than 177 volts, then check and repair the power
circuit to the draft motor. If the voltage is greater
than 176 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 176 volts and the motor is turning,
then check the centrifugal switch wiring between
the ICB and the draft motor. If ok, then discon-
nect 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 cen-
trifugal switch wiring per the wiring diagram.
Place the gas valve in the on position and verify
proper furnace operation.
2. If the flash code indicates the switch is closed with
the draft (inducer) motor off (flash code 3), then
disconnect the 9 pin connector from the ICB and
measure the continuity of the centrifugal switch
with a battery powered test light or an ohm meter
between terminals 3 and 8 of the harness connec-
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