290699-YIM-B-0607
Unitary Products Group
51
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 sec-
tion. 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 33 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 indica-
tion 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 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 ver-
ify 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 connection
between the harness connector and the ICB connector
or a broken wire exists in the harness. With the har-
ness 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 drag-
ging, 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 fur-
nace operation.
b.
Restore power to unit and induce a call for heat. Mea-
sure the voltage across the two draft motor leads
(white and red). 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 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 discon-
necting 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 recon-
nect the centrifugal switch wiring per the wiring dia-
gram. 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 discon-
nect 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 termi-
nals 3 and 8 of the harness connector. If a closed cir-
