175615-YIM-A-0306
Unitary Products Group
51
4. Cracked heat exchanger tube(s). If a heat
exchanger tube or tubes is cracked, then the flow
through the heat exchanger is restricted and the
flame will either roll out of the tube inlet or heat will
build to an abnormal level in the burner area. This
can usually be determined by observing burner
flame with and without indoor blower operation. If
the flame changes when the blower is running
compared to when it is not, then visually inspect
the heat exchanger tubes.
If all of the above are found to be in good condition or
within the operating ranges, then set the gas valve to
the off position and temporarily apply control voltage
(~24 volts) to pin 6 of the 9 pin ICB connector. With
power applied to the unit, if the ICB LED continues to
flash a code 7, then replace the ICB and return unit to
operation (you must remove the temporary voltage to
pin 6 before the gas valve is turned on). If the ICB LED
flashes a heartbeat, then replace the rollout switch,
remove the temporary voltage applied to pin 6, turn on
the gas valve, restart the furnace and verify proper
operation of the furnace.
UNEXPECTED FLAME PRESENCE
If a flame is present without a call for heat (flash code
8), then the ICB will continue operation of the draft
motor and the UCB will call for indoor operation when
either of the temperature limit opens. If the unit is cor-
rectly wired and there is not a call for heat, then check
for control voltage to the gas valve. If control voltage
exists at the gas valve, then replace the ICB. If voltage
is not present at the gas valve, then replace the gas
valve.
SYMPTOMATIC TROUBLESHOOTING
On calls for heating, the draft motor operates and the
furnace lights but the supply air blower motor does not
energize after a short delay (the room thermostat fan
switch is in “AUTO” position).
1. Place the thermostat fan switch in the “ON” posi-
tion. If the supply air blower motor energizes, go to
Step 10.
2. If the supply air blower motor does not energize
when the fan switch is set to “ON,” check that line
voltage is being supplied to the contacts of the M2
contactor, and that the contactor is pulled in. Check
for loose wiring between the contactor and the sup-
ply air blower motor.
3. If M2 is pulled in and voltage is supplied at M2,
lightly touch the supply air blower motor housing. If
it is hot, the motor may be off on inherent protec-
tion. Cancel any thermostat calls and set the fan
switch to “AUTO”, wait for the internal overload to
reset. Test again when cool.
4. If M2 is not pulled in, check for 24 volts at the M2
coil. If 24 volts is present at M2 but M2 is not pulled
in, replace the contactor.
5. Failing the above, if there is line voltage supplied at
M2, M2 is pulled in, and the supply air blower
motor still does not operate, replace the motor.
6. If 24 volts is not present at M2, check that 24 volts is
present at the supply air blower motor terminal on
the UCB. If 24 volts is present at the UCB terminal,
check for loose wiring between the UCB and M2.
7. If 24 volts is not present at the UCB supply air
blower motor terminal, check for 24 volts from the
room thermostat. If 24 volts is not present from the
room thermostat, check for the following:
a. Proper operation of the room thermostat (contact
between R and G with the fan switch in the “ON”
position and in the “AUTO” position during operation
calls).
b. Proper wiring between the room thermostat and the
UCB.
c. Loose wiring from the room thermostat to the UCB.
8. If 24 volts is present at the room thermostat but not
at the UCB, check for proper wiring between the
thermostat and the UCB, i.e. that the thermostat G
terminal is connected to the G terminal of the UCB,
and for loose wiring.
9. If the thermostat and UCB are properly wired,
replace the UCB.
10. If the blower motor runs with the fan switch in the
“ON” position but does not run shortly after the fur-
nace has ignited when the fan switch is in the
“AUTO” position, check the room thermostat for
contact between R and G during “W1” calls.
On calls for heating, the supply air blower operates but
the draft motor does not (the room thermostat fan
switch is in the “AUTO” position).
1. The draft motor has inherent protection. If the
motor shell is hot to the touch, wait for the internal
overload to reset.
2. If the motor shell is cold with the room thermostat
calling for heat, check if 24 volts is present at the
